Add post video upload.

post_images.kind is image or video. A post can keep one video alongside up to four images.

Reviewed-on: #21
Co-authored-by: codegirl-007 <s.raide@gmail.com>

.env.example

@@ -26,3 +26,7 @@ SECURE_COOKIE=0
 # SPACES_BUCKET=your-bucket
 # SPACES_ENDPOINT=https://nyc3.digitaloceanspaces.com
 # SPACES_CDN_BASE=https://your-bucket.nyc3.cdn.digitaloceanspaces.com
+# Discord bot subscriber. Leave unset to disable.
+# DISCORD_BOT_TOKEN=
+# DISCORD_CHANNEL_ID=
+# DISCORD_ADMIN_MAP=123456789012345678:plumber,234567890123456789:otheradmin

cmd/server/main.go

@@ -17,6 +17,8 @@ import (
 
 	"plumber"
 	"plumber/internal/blob"
+	"plumber/internal/discord"
+	"plumber/internal/events"
 	"plumber/internal/mail"
 	"plumber/internal/store"
 	"plumber/internal/web"
@@ -34,7 +36,16 @@ func main() {
 	if err != nil {
 		log.Fatalf("mail: %v", err)
 	}
-	handler := newHandler(db, sessions, uploader, notifier)
+	bus := events.New()
+	mail.Subscribe(bus, store.NewPostgres(db), notifier)
+	bot, err := discord.FromEnv(store.NewDiscordLinks(db), bus, store.NewPostgres(db))
+	if err != nil {
+		log.Fatalf("discord: %v", err)
+	}
+	if bot != nil {
+		defer bot.Close()
+	}
+	handler := newHandler(db, sessions, uploader, bus)
 	run(&http.Server{
 		Addr:              listenAddr(),
 		Handler:           handler,
@@ -58,13 +69,14 @@ func openDB() (*sql.DB, *store.SessionStore) {
 	return db, sessions
 }
 
-func newHandler(db *sql.DB, sessions *store.SessionStore, uploader blob.Uploader, notifier mail.Notifier) http.Handler {
+func newHandler(db *sql.DB, sessions *store.SessionStore, uploader blob.Uploader, bus events.Publisher) http.Handler {
 	srv, err := web.New(store.NewPostgres(db), sessions.Store(), plumber.TemplateFS, plumber.StaticFS, web.Config{
 		AdminSetupSecret: strings.TrimSpace(os.Getenv("ADMIN_SETUP_SECRET")),
 		SecureCookie:     secureCookieFromEnv(),
 		TrustedProxies:   parseTrustedProxies(os.Getenv("TRUSTED_PROXY_CIDRS")),
 		Blob:             uploader,
-		Mail:             notifier,
+		Events:           bus,
+		BaseURL:          strings.TrimRight(strings.TrimSpace(os.Getenv("APP_BASE_URL")), "/"),
 	})
 	if err != nil {
 		log.Fatalf("server: %v", err)

db/queries/discord_links.sql

@@ -0,0 +1,32 @@
+-- name: GetDiscordPostLinkByPostID :one
+SELECT post_id, discord_message_id, discord_thread_id, created_at
+FROM discord_post_links
+WHERE post_id = sqlc.arg(post_id);
+
+-- name: GetDiscordPostLinkByMessageID :one
+SELECT post_id, discord_message_id, discord_thread_id, created_at
+FROM discord_post_links
+WHERE discord_message_id = sqlc.arg(discord_message_id);
+
+-- name: GetDiscordPostLinkByThreadID :one
+SELECT post_id, discord_message_id, discord_thread_id, created_at
+FROM discord_post_links
+WHERE discord_thread_id = sqlc.arg(discord_thread_id)
+  AND discord_thread_id <> '';
+
+-- name: UpsertDiscordPostLink :exec
+INSERT INTO discord_post_links (
+  post_id, discord_message_id, discord_thread_id, created_at
+)
+VALUES (
+  sqlc.arg(post_id),
+  sqlc.arg(discord_message_id),
+  sqlc.arg(discord_thread_id),
+  sqlc.arg(created_at)
+)
+ON CONFLICT (post_id) DO UPDATE SET
+  discord_message_id = EXCLUDED.discord_message_id,
+  discord_thread_id = CASE
+    WHEN EXCLUDED.discord_thread_id <> '' THEN EXCLUDED.discord_thread_id
+    ELSE discord_post_links.discord_thread_id
+  END;

db/queries/posts.sql

@@ -63,7 +63,7 @@ WHERE id = sqlc.arg(id);
 
 -- name: CreatePostImage :exec
 INSERT INTO post_images (
-  id, post_id, object_key, public_url, description, position, width, height, created_at
+  id, post_id, object_key, public_url, description, kind, position, width, height, created_at
 )
 VALUES (
   sqlc.arg(id),
@@ -71,6 +71,7 @@ VALUES (
   sqlc.arg(object_key),
   sqlc.arg(public_url),
   sqlc.arg(description),
+  sqlc.arg(kind),
   sqlc.arg(position),
   sqlc.arg(width),
   sqlc.arg(height),
@@ -83,7 +84,7 @@ WHERE post_id = sqlc.arg(post_id);
 
 -- name: ListPostImages :many
 SELECT
-  id, post_id, object_key, public_url, description, position, width, height, created_at
+  id, post_id, object_key, public_url, description, kind, position, width, height, created_at
 FROM post_images
 WHERE post_id = sqlc.arg(post_id)
 ORDER BY position;
@@ -102,7 +103,7 @@ WITH RECURSIVE thread AS (
 )
 SELECT
   images.id, images.post_id, images.object_key, images.public_url,
-  images.description, images.position, images.width, images.height, images.created_at
+  images.description, images.kind, images.position, images.width, images.height, images.created_at
 FROM post_images images
 JOIN thread ON thread.id = images.post_id
 ORDER BY images.post_id, images.position;

go.mod

@@ -7,10 +7,12 @@ require (
 	github.com/aws/aws-sdk-go-v2 v1.43.7
 	github.com/aws/aws-sdk-go-v2/credentials v1.19.37
 	github.com/aws/aws-sdk-go-v2/service/s3 v1.107.3
+	github.com/bwmarrin/discordgo v0.29.0
 	github.com/go-chi/chi/v5 v5.3.1
 	github.com/google/uuid v1.6.0
 	github.com/jackc/pgx/v5 v5.10.0
 	github.com/joho/godotenv v1.5.1
+	github.com/resend/resend-go/v3 v3.16.0
 	github.com/rwcarlsen/goexif v0.0.0-20190401172101-9e8deecbddbd
 	golang.org/x/crypto v0.55.0
 	golang.org/x/image v0.45.0
@@ -26,10 +28,11 @@ require (
 	github.com/aws/aws-sdk-go-v2/service/internal/presigned-url v1.13.38 // indirect
 	github.com/aws/aws-sdk-go-v2/service/internal/s3shared v1.19.39 // indirect
 	github.com/aws/smithy-go v1.27.8 // indirect
+	github.com/gorilla/websocket v1.4.2 // indirect
 	github.com/jackc/pgpassfile v1.0.0 // indirect
 	github.com/jackc/pgservicefile v0.0.0-20240606120523-5a60cdf6a761 // indirect
 	github.com/jackc/puddle/v2 v2.2.2 // indirect
-	github.com/resend/resend-go/v3 v3.16.0 // indirect
 	golang.org/x/sync v0.22.0 // indirect
+	golang.org/x/sys v0.47.0 // indirect
 	golang.org/x/text v0.41.0 // indirect
 )

go.sum

@@ -24,6 +24,8 @@ github.com/aws/aws-sdk-go-v2/service/s3 v1.107.3 h1:IKoCZqfWfZzSBi16QFQ+QcbQ3LRQ
 github.com/aws/aws-sdk-go-v2/service/s3 v1.107.3/go.mod h1:RBpRcXiM4s2pOInVs32GsBonnje+fiAj4mcrStRmlCA=
 github.com/aws/smithy-go v1.27.8 h1:FR0dxZfIlV7Z8eh2iHfIofdunw382XsDV3Mxt9nUvRY=
 github.com/aws/smithy-go v1.27.8/go.mod h1:YE2RhdIuDbA5E5bTdciG9KrW3+TiEONeUWCqxX9i1Fc=
+github.com/bwmarrin/discordgo v0.29.0 h1:FmWeXFaKUwrcL3Cx65c20bTRW+vOb6k8AnaP+EgjDno=
+github.com/bwmarrin/discordgo v0.29.0/go.mod h1:NJZpH+1AfhIcyQsPeuBKsUtYrRnjkyu0kIVMCHkZtRY=
 github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
@@ -31,6 +33,8 @@ github.com/go-chi/chi/v5 v5.3.1 h1:3j4HZLGZQ3JpMCrPJF/Jl3mYJfWLKBfNJ6quurUGCf8=
 github.com/go-chi/chi/v5 v5.3.1/go.mod h1:R+tYY2hNuVUUjxoPtqUdgBqevM9s9njzkTLutVsOCto=
 github.com/google/uuid v1.6.0 h1:NIvaJDMOsjHA8n1jAhLSgzrAzy1Hgr+hNrb57e+94F0=
 github.com/google/uuid v1.6.0/go.mod h1:TIyPZe4MgqvfeYDBFedMoGGpEw/LqOeaOT+nhxU+yHo=
+github.com/gorilla/websocket v1.4.2 h1:+/TMaTYc4QFitKJxsQ7Yye35DkWvkdLcvGKqM+x0Ufc=
+github.com/gorilla/websocket v1.4.2/go.mod h1:YR8l580nyteQvAITg2hZ9XVh4b55+EU/adAjf1fMHhE=
 github.com/jackc/pgpassfile v1.0.0 h1:/6Hmqy13Ss2zCq62VdNG8tM1wchn8zjSGOBJ6icpsIM=
 github.com/jackc/pgpassfile v1.0.0/go.mod h1:CEx0iS5ambNFdcRtxPj5JhEz+xB6uRky5eyVu/W2HEg=
 github.com/jackc/pgservicefile v0.0.0-20240606120523-5a60cdf6a761 h1:iCEnooe7UlwOQYpKFhBabPMi4aNAfoODPEFNiAnClxo=
@@ -52,14 +56,22 @@ github.com/stretchr/testify v1.3.0/go.mod h1:M5WIy9Dh21IEIfnGCwXGc5bZfKNJtfHm1UV
 github.com/stretchr/testify v1.7.0/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
 github.com/stretchr/testify v1.11.1 h1:7s2iGBzp5EwR7/aIZr8ao5+dra3wiQyKjjFuvgVKu7U=
 github.com/stretchr/testify v1.11.1/go.mod h1:wZwfW3scLgRK+23gO65QZefKpKQRnfz6sD981Nm4B6U=
+golang.org/x/crypto v0.0.0-20210421170649-83a5a9bb288b/go.mod h1:T9bdIzuCu7OtxOm1hfPfRQxPLYneinmdGuTeoZ9dtd4=
 golang.org/x/crypto v0.55.0 h1:+KWHjbgOaAQ66dh/YlkZKHlz9ZUlq61AFirAR9ntP8M=
 golang.org/x/crypto v0.55.0/go.mod h1:uq0V9dE/fzQuJtbnL+2EhWOE63vo164FY8xqEnV9xis=
 golang.org/x/image v0.45.0 h1:FMb1nTbH5H9vF55SriQHgFw5GnNL9Jg6L25BwXKzhB0=
 golang.org/x/image v0.45.0/go.mod h1:n62x/7RqlwXDvGsSU4u6IUTUf6KghUZ9Bt7cG/T9Fx4=
+golang.org/x/net v0.0.0-20210226172049-e18ecbb05110/go.mod h1:m0MpNAwzfU5UDzcl9v0D8zg8gWTRqZa9RBIspLL5mdg=
 golang.org/x/sync v0.22.0 h1:SZjpbeLmrCk4xhRSZFNZW5gFUeCeFgjekvI/+gfScek=
 golang.org/x/sync v0.22.0/go.mod h1:9xrNwdLfx4jkKbNva9FpL6vEN7evnE43NNNJQ2LF3+0=
+golang.org/x/sys v0.0.0-20201119102817-f84b799fce68/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+golang.org/x/sys v0.47.0 h1:o7XGOvZQCADBQQ4Y7VNq2dRWQR7JmOUW8Kxx4ZsNgWs=
+golang.org/x/sys v0.47.0/go.mod h1:4GL1E5IUh+htKOUEOaiffhrAeqysfVGipDYzABqnCmw=
+golang.org/x/term v0.0.0-20201126162022-7de9c90e9dd1/go.mod h1:bj7SfCRtBDWHUb9snDiAeCFNEtKQo2Wmx5Cou7ajbmo=
+golang.org/x/text v0.3.3/go.mod h1:5Zoc/QRtKVWzQhOtBMvqHzDpF6irO9z98xDceosuGiQ=
 golang.org/x/text v0.41.0 h1:vz/seA0lnX87Othu2f/0L24RcgrXD9/YFTSuGjj3rH8=
 golang.org/x/text v0.41.0/go.mod h1:jvf1O8ajNzZqhSrQBPbutR/EB83Cc0CFrezNQIwbb5M=
+golang.org/x/tools v0.0.0-20180917221912-90fa682c2a6e/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
 gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=

internal/discord/api.go

@@ -0,0 +1,106 @@
+package discord
+
+import (
+	"context"
+
+	"github.com/bwmarrin/discordgo"
+)
+
+// API is the Discord REST surface used by the outbound subscriber.
+type API interface {
+	SendToChannel(ctx context.Context, channelID string, msg Message) (messageID string, err error)
+	StartThread(ctx context.Context, channelID, name string) (threadID string, err error)
+	SendToThread(ctx context.Context, threadID string, msg Message) (messageID string, err error)
+	Edit(ctx context.Context, channelID, messageID string, msg Message) error
+	Close() error
+}
+
+type sessionAPI struct {
+	session *discordgo.Session
+}
+
+func (s *sessionAPI) SendToChannel(_ context.Context, channelID string, msg Message) (string, error) {
+	sent, err := s.session.ChannelMessageSendComplex(channelID, toMessageSend(msg))
+	if err != nil {
+		return "", err
+	}
+	return sent.ID, nil
+}
+
+func (s *sessionAPI) StartThread(_ context.Context, channelID, name string) (string, error) {
+	thread, err := s.session.ThreadStartComplex(channelID, &discordgo.ThreadStart{
+		Name:                name,
+		Type:                discordgo.ChannelTypeGuildPublicThread,
+		AutoArchiveDuration: 10080,
+	})
+	if err != nil {
+		return "", err
+	}
+	return thread.ID, nil
+}
+
+func (s *sessionAPI) SendToThread(ctx context.Context, threadID string, msg Message) (string, error) {
+	return s.SendToChannel(ctx, threadID, msg)
+}
+
+func (s *sessionAPI) Edit(_ context.Context, channelID, messageID string, msg Message) error {
+	content := messageContent(msg)
+	embeds := toEmbeds(msg)
+	_, err := s.session.ChannelMessageEditComplex(&discordgo.MessageEdit{
+		ID:      messageID,
+		Channel: channelID,
+		Content: &content,
+		Embeds:  &embeds,
+	})
+	return err
+}
+
+func (s *sessionAPI) Close() error {
+	if s == nil || s.session == nil {
+		return nil
+	}
+	return s.session.Close()
+}
+
+func toMessageSend(msg Message) *discordgo.MessageSend {
+	return &discordgo.MessageSend{
+		Content:         messageContent(msg),
+		Embeds:          toEmbeds(msg),
+		AllowedMentions: &discordgo.MessageAllowedMentions{},
+	}
+}
+
+func toEmbeds(msg Message) []*discordgo.MessageEmbed {
+	main := &discordgo.MessageEmbed{
+		Title:       msg.Title,
+		URL:         publicURL(msg.URL),
+		Description: msg.Description,
+		Color:       embedColor,
+	}
+	if msg.City != "" {
+		main.Fields = append(main.Fields, &discordgo.MessageEmbedField{
+			Name:   "City",
+			Value:  msg.City,
+			Inline: true,
+		})
+	}
+	if msg.Author != "" {
+		main.Fields = append(main.Fields, &discordgo.MessageEmbedField{
+			Name:   "Author",
+			Value:  msg.Author,
+			Inline: true,
+		})
+	}
+	embeds := []*discordgo.MessageEmbed{main}
+	for i, url := range msg.ImageURLs {
+		if i == 0 {
+			main.Image = &discordgo.MessageEmbedImage{URL: url}
+			continue
+		}
+		embeds = append(embeds, &discordgo.MessageEmbed{
+			Color: embedColor,
+			Image: &discordgo.MessageEmbedImage{URL: url},
+		})
+	}
+	return embeds
+}

internal/discord/bot.go

@@ -0,0 +1,202 @@
+package discord
+
+import (
+	"context"
+	"database/sql"
+	"errors"
+	"fmt"
+	"log"
+	"os"
+	"strings"
+	"time"
+
+	"github.com/bwmarrin/discordgo"
+
+	"plumber/internal/events"
+	"plumber/internal/store"
+)
+
+const discordTimeout = 15 * time.Second
+
+// Bot posts site events to a Discord channel and owns post-to-message links.
+type Bot struct {
+	channelID string
+	links     store.DiscordLinkStore
+	api       API
+	store     store.Store
+	bus       events.Publisher
+	admins    map[string]string
+	botUserID string
+}
+
+// New constructs an outbound subscriber. Tests inject a fake API.
+func New(channelID string, links store.DiscordLinkStore, api API) *Bot {
+	return &Bot{channelID: strings.TrimSpace(channelID), links: links, api: api}
+}
+
+// FromEnv builds a bot when Discord env is set. Missing config is a no-op.
+func FromEnv(links store.DiscordLinkStore, bus *events.Bus, st store.Store) (*Bot, error) {
+	token := strings.TrimSpace(os.Getenv("DISCORD_BOT_TOKEN"))
+	channelID := strings.TrimSpace(os.Getenv("DISCORD_CHANNEL_ID"))
+	if token == "" && channelID == "" {
+		return nil, nil
+	}
+	if token == "" {
+		return nil, fmt.Errorf("DISCORD_BOT_TOKEN is required when DISCORD_CHANNEL_ID is set")
+	}
+	if channelID == "" {
+		return nil, fmt.Errorf("DISCORD_CHANNEL_ID is required when DISCORD_BOT_TOKEN is set")
+	}
+	if links == nil {
+		return nil, fmt.Errorf("discord links store is required")
+	}
+	session, err := discordgo.New("Bot " + token)
+	if err != nil {
+		return nil, err
+	}
+	session.Identify.Intents = discordgo.IntentsGuilds | discordgo.IntentsGuildMessages | discordgo.IntentsMessageContent
+	bot := New(channelID, links, &sessionAPI{session: session})
+	bot.store = st
+	bot.bus = bus
+	bot.admins = parseAdminMap(os.Getenv("DISCORD_ADMIN_MAP"))
+	session.AddHandler(bot.onMessageCreate)
+	if bus != nil {
+		bus.Subscribe(bot.Handle)
+	}
+	if err := session.Open(); err != nil {
+		_ = session.Close()
+		return nil, fmt.Errorf("discord gateway: %w", err)
+	}
+	if session.State != nil && session.State.User != nil {
+		bot.botUserID = session.State.User.ID
+	}
+	log.Printf("discord: subscriber enabled")
+	return bot, nil
+}
+
+// Close releases the Discord session.
+func (b *Bot) Close() error {
+	if b == nil || b.api == nil {
+		return nil
+	}
+	return b.api.Close()
+}
+
+// Handle processes one site event. Failures are logged and do not fail the request.
+func (b *Bot) Handle(_ context.Context, ev any) {
+	if b == nil {
+		return
+	}
+	ctx, cancel := context.WithTimeout(context.Background(), discordTimeout)
+	defer cancel()
+	switch e := ev.(type) {
+	case events.PostCreated:
+		b.onCreated(ctx, e.PostEvent)
+	case events.PostUpdated:
+		b.onUpdated(ctx, e.PostEvent)
+	}
+}
+
+func (b *Bot) onCreated(ctx context.Context, ev events.PostEvent) {
+	_, err := b.links.GetByPostID(ctx, ev.PostID)
+	if err == nil {
+		return
+	}
+	if !errors.Is(err, sql.ErrNoRows) {
+		log.Printf("discord: load link %s: %v", ev.PostID, err)
+		return
+	}
+	if isRoot(ev) {
+		b.createRoot(ctx, ev)
+		return
+	}
+	b.createReply(ctx, ev)
+}
+
+func (b *Bot) onUpdated(ctx context.Context, ev events.PostEvent) {
+	link, err := b.links.GetByPostID(ctx, ev.PostID)
+	if err != nil {
+		if errors.Is(err, sql.ErrNoRows) {
+			b.onCreated(ctx, ev)
+			return
+		}
+		log.Printf("discord: load link %s: %v", ev.PostID, err)
+		return
+	}
+	channelID, err := b.editChannel(ctx, ev, link)
+	if err != nil {
+		log.Printf("discord: edit channel %s: %v", ev.PostID, err)
+		return
+	}
+	if err := b.api.Edit(ctx, channelID, link.MessageID, formatMessage(ev)); err != nil {
+		log.Printf("discord: edit %s: %v", ev.PostID, err)
+		return
+	}
+	log.Printf("discord: edited %s", ev.PostID)
+}
+
+func (b *Bot) createRoot(ctx context.Context, ev events.PostEvent) {
+	msg := formatMessage(ev)
+	threadID, err := b.api.StartThread(ctx, b.channelID, msg.ThreadName)
+	if err != nil {
+		log.Printf("discord: start thread %s: %v", ev.PostID, err)
+		return
+	}
+	messageID, err := b.api.SendToThread(ctx, threadID, msg)
+	if err != nil {
+		log.Printf("discord: send root %s: %v", ev.PostID, err)
+		return
+	}
+	if err := b.links.Upsert(ctx, store.DiscordLink{
+		PostID:    ev.PostID,
+		MessageID: messageID,
+		ThreadID:  threadID,
+	}); err != nil {
+		log.Printf("discord: save root link %s: %v", ev.PostID, err)
+		return
+	}
+	log.Printf("discord: posted root %s", ev.PostID)
+}
+
+func (b *Bot) createReply(ctx context.Context, ev events.PostEvent) {
+	root, err := b.links.GetByPostID(ctx, ev.RootID)
+	if err != nil {
+		if errors.Is(err, sql.ErrNoRows) {
+			log.Printf("discord: skip reply %s: no root thread", ev.PostID)
+			return
+		}
+		log.Printf("discord: load root link %s: %v", ev.RootID, err)
+		return
+	}
+	if strings.TrimSpace(root.ThreadID) == "" {
+		log.Printf("discord: skip reply %s: no root thread", ev.PostID)
+		return
+	}
+	messageID, err := b.api.SendToThread(ctx, root.ThreadID, formatMessage(ev))
+	if err != nil {
+		log.Printf("discord: send reply %s: %v", ev.PostID, err)
+		return
+	}
+	if err := b.links.Upsert(ctx, store.DiscordLink{
+		PostID:    ev.PostID,
+		MessageID: messageID,
+	}); err != nil {
+		log.Printf("discord: save reply link %s: %v", ev.PostID, err)
+		return
+	}
+	log.Printf("discord: posted reply %s", ev.PostID)
+}
+
+func (b *Bot) editChannel(ctx context.Context, ev events.PostEvent, link *store.DiscordLink) (string, error) {
+	if strings.TrimSpace(link.ThreadID) != "" {
+		return link.ThreadID, nil
+	}
+	root, err := b.links.GetByPostID(ctx, ev.RootID)
+	if err != nil {
+		return "", err
+	}
+	if strings.TrimSpace(root.ThreadID) == "" {
+		return "", fmt.Errorf("root %s has no thread", ev.RootID)
+	}
+	return root.ThreadID, nil
+}

internal/discord/bot_test.go

@@ -0,0 +1,291 @@
+package discord
+
+import (
+	"context"
+	"strconv"
+	"strings"
+	"sync"
+	"testing"
+
+	"plumber/internal/events"
+	"plumber/internal/store"
+)
+
+type recordedSend struct {
+	Kind      string
+	ChannelID string
+	Name      string
+	Msg       Message
+}
+
+type fakeAPI struct {
+	mu       sync.Mutex
+	sends    []recordedSend
+	edits    []recordedSend
+	next     int
+	failSend error
+}
+
+func (f *fakeAPI) SendToChannel(_ context.Context, channelID string, msg Message) (string, error) {
+	return f.record("channel", channelID, "", msg)
+}
+
+func (f *fakeAPI) StartThread(_ context.Context, channelID, name string) (string, error) {
+	f.mu.Lock()
+	defer f.mu.Unlock()
+	f.next++
+	id := "thread-" + strconv.Itoa(f.next)
+	f.sends = append(f.sends, recordedSend{
+		Kind:      "thread",
+		ChannelID: channelID,
+		Name:      name,
+		Msg:       Message{ThreadName: name},
+	})
+	return id, nil
+}
+
+func (f *fakeAPI) SendToThread(_ context.Context, threadID string, msg Message) (string, error) {
+	return f.record("thread-msg", threadID, "", msg)
+}
+
+func (f *fakeAPI) Edit(_ context.Context, channelID, messageID string, msg Message) error {
+	f.mu.Lock()
+	defer f.mu.Unlock()
+	f.edits = append(f.edits, recordedSend{
+		Kind:      "edit",
+		ChannelID: channelID,
+		Name:      messageID,
+		Msg:       msg,
+	})
+	return nil
+}
+
+func (f *fakeAPI) Close() error { return nil }
+
+func (f *fakeAPI) record(kind, channelID, name string, msg Message) (string, error) {
+	f.mu.Lock()
+	defer f.mu.Unlock()
+	if f.failSend != nil {
+		return "", f.failSend
+	}
+	f.next++
+	id := "msg-" + strconv.Itoa(f.next)
+	f.sends = append(f.sends, recordedSend{Kind: kind, ChannelID: channelID, Name: name, Msg: msg})
+	return id, nil
+}
+
+func TestOutboundRootReplyAndEdit(t *testing.T) {
+	t.Parallel()
+
+	links := newMemoryLinks()
+	api := &fakeAPI{}
+	bot := New("channel-1", links, api)
+	ctx := context.Background()
+
+	root := events.PostEvent{
+		PostID:     "root-1",
+		RootID:     "root-1",
+		Title:      "Leaky sink",
+		Body:       "Water under the cabinet.",
+		City:       "Oakland",
+		AuthorName: "sam",
+		Permalink:  "https://www.askaplumberfirst.com/questions/root-1#post-root-1",
+		Images:     []events.Image{{URL: "https://cdn.example/a.jpg"}, {URL: "https://cdn.example/b.jpg"}},
+	}
+	bot.Handle(ctx, events.PostCreated{PostEvent: root})
+
+	if len(api.sends) != 2 ||
+		api.sends[0].Kind != "thread" ||
+		api.sends[1].Kind != "thread-msg" {
+		t.Fatalf("root sends = %+v", api.sends)
+	}
+	if api.sends[0].ChannelID != "channel-1" ||
+		api.sends[0].Name != "sam asks: Leaky sink" ||
+		api.sends[1].ChannelID != "thread-1" {
+		t.Fatalf("root routing = %+v", api.sends)
+	}
+	if got := api.sends[1].Msg.ImageURLs; len(got) != 2 || got[0] != "https://cdn.example/a.jpg" {
+		t.Fatalf("root images = %v", got)
+	}
+	link, err := links.GetByPostID(ctx, "root-1")
+	if err != nil || link.MessageID != "msg-2" || link.ThreadID != "thread-1" {
+		t.Fatalf("root link = %+v, %v", link, err)
+	}
+
+	reply := events.PostEvent{
+		PostID:     "reply-1",
+		RootID:     "root-1",
+		ParentID:   "root-1",
+		Body:       "Replace the cartridge.",
+		AuthorName: "plumber",
+		Permalink:  "https://www.askaplumberfirst.com/questions/root-1#post-reply-1",
+	}
+	bot.Handle(ctx, events.PostCreated{PostEvent: reply})
+	if len(api.sends) != 3 || api.sends[2].Kind != "thread-msg" || api.sends[2].ChannelID != "thread-1" {
+		t.Fatalf("reply sends = %+v", api.sends)
+	}
+	replyLink, err := links.GetByPostID(ctx, "reply-1")
+	if err != nil || replyLink.MessageID != "msg-3" || replyLink.ThreadID != "" {
+		t.Fatalf("reply link = %+v, %v", replyLink, err)
+	}
+
+	root.Body = "Updated leak."
+	bot.Handle(ctx, events.PostUpdated{PostEvent: root})
+	if len(api.edits) != 1 || api.edits[0].ChannelID != "thread-1" || api.edits[0].Name != "msg-2" {
+		t.Fatalf("root edit = %+v", api.edits)
+	}
+	if api.edits[0].Msg.Description != "Updated leak." {
+		t.Fatalf("root edit body = %+v", api.edits[0].Msg)
+	}
+
+	reply.Body = "Use a ceramic cartridge."
+	bot.Handle(ctx, events.PostUpdated{PostEvent: reply})
+	if len(api.edits) != 2 || api.edits[1].ChannelID != "thread-1" || api.edits[1].Name != "msg-3" {
+		t.Fatalf("reply edit = %+v", api.edits)
+	}
+}
+
+func TestOutboundSkipsReplyWithoutRootLink(t *testing.T) {
+	t.Parallel()
+
+	api := &fakeAPI{}
+	bot := New("channel-1", newMemoryLinks(), api)
+	bot.Handle(context.Background(), events.PostCreated{PostEvent: events.PostEvent{
+		PostID:   "reply-1",
+		RootID:   "missing",
+		ParentID: "missing",
+		Body:     "Orphan reply",
+	}})
+	if len(api.sends) != 0 {
+		t.Fatalf("unexpected sends %+v", api.sends)
+	}
+}
+
+func TestOutboundSkipsAlreadyLinkedPost(t *testing.T) {
+	t.Parallel()
+
+	links := newMemoryLinks()
+	api := &fakeAPI{}
+	bot := New("channel-1", links, api)
+	if err := links.Upsert(context.Background(), store.DiscordLink{
+		PostID:    "reply-1",
+		MessageID: "d-reply-1",
+	}); err != nil {
+		t.Fatal(err)
+	}
+	if err := links.Upsert(context.Background(), store.DiscordLink{
+		PostID:    "root-1",
+		MessageID: "d-root",
+		ThreadID:  "thread-1",
+	}); err != nil {
+		t.Fatal(err)
+	}
+	bot.Handle(context.Background(), events.PostCreated{PostEvent: events.PostEvent{
+		PostID:   "reply-1",
+		RootID:   "root-1",
+		ParentID: "root-1",
+		Body:     "Already on Discord.",
+	}})
+	if len(api.sends) != 0 {
+		t.Fatalf("echoed already-linked reply: %+v", api.sends)
+	}
+}
+
+func TestOutboundUpdateWithoutLinkCreates(t *testing.T) {
+	t.Parallel()
+
+	links := newMemoryLinks()
+	api := &fakeAPI{}
+	bot := New("channel-1", links, api)
+	bot.Handle(context.Background(), events.PostUpdated{PostEvent: events.PostEvent{
+		PostID: "root-2",
+		RootID: "root-2",
+		Title:  "Late question",
+		Body:   "Created while Discord was down.",
+	}})
+	link, err := links.GetByPostID(context.Background(), "root-2")
+	if err != nil || link.ThreadID == "" || len(api.sends) != 2 {
+		t.Fatalf("late create link=%+v sends=%+v err=%v", link, api.sends, err)
+	}
+}
+
+func TestFormatMessage(t *testing.T) {
+	t.Parallel()
+
+	got := formatMessage(events.PostEvent{
+		Title:      "Leaky sink",
+		Body:       "It drips.",
+		City:       "Oakland",
+		AuthorName: "sam",
+		Permalink:  "https://example.com/q",
+		Images:     []events.Image{{URL: "https://cdn.example/a.jpg", Description: "ignored"}},
+	})
+	if got.Title != "Leaky sink" ||
+		got.Description != "It drips." ||
+		got.City != "Oakland" ||
+		got.Author != "sam" ||
+		got.URL != "https://example.com/q" ||
+		got.ThreadName != "sam asks: Leaky sink" ||
+		len(got.ImageURLs) != 1 {
+		t.Fatalf("format = %+v", got)
+	}
+
+	reply := formatMessage(events.PostEvent{Body: "Thanks", AuthorName: ""})
+	if reply.Title != "Reply" || reply.Author != "Someone" || reply.ThreadName != "Someone asks: Question" {
+		t.Fatalf("reply format = %+v", reply)
+	}
+	content := messageContent(got)
+	if strings.Contains(content, "Leaky sink") ||
+		!strings.Contains(content, "It drips.") ||
+		!strings.Contains(content, "Oakland") {
+		t.Fatalf("content = %q", content)
+	}
+	if publicURL("/questions/x") != "" || publicURL("http://localhost:8080/q") != "" {
+		t.Fatal("localhost or relative permalink should not be an embed URL")
+	}
+}
+
+func TestFromEnvDisabled(t *testing.T) {
+	t.Setenv("DISCORD_BOT_TOKEN", "")
+	t.Setenv("DISCORD_CHANNEL_ID", "")
+	bot, err := FromEnv(newMemoryLinks(), nil, nil)
+	if err != nil || bot != nil {
+		t.Fatalf("disabled FromEnv = (%v, %v)", bot, err)
+	}
+}
+
+func TestFromEnvRequiresBoth(t *testing.T) {
+	t.Setenv("DISCORD_BOT_TOKEN", "token")
+	t.Setenv("DISCORD_CHANNEL_ID", "")
+	if _, err := FromEnv(newMemoryLinks(), nil, nil); err == nil {
+		t.Fatal("expected error when channel is missing")
+	}
+	t.Setenv("DISCORD_BOT_TOKEN", "")
+	t.Setenv("DISCORD_CHANNEL_ID", "channel")
+	if _, err := FromEnv(newMemoryLinks(), nil, nil); err == nil {
+		t.Fatal("expected error when token is missing")
+	}
+}
+
+func TestMemoryLinkUpsertKeepsThread(t *testing.T) {
+	t.Parallel()
+
+	links := newMemoryLinks()
+	ctx := context.Background()
+	if err := links.Upsert(ctx, store.DiscordLink{PostID: "p", MessageID: "m1", ThreadID: "t1"}); err != nil {
+		t.Fatal(err)
+	}
+	if err := links.Upsert(ctx, store.DiscordLink{PostID: "p", MessageID: "m2"}); err != nil {
+		t.Fatal(err)
+	}
+	got, err := links.GetByPostID(ctx, "p")
+	if err != nil || got.MessageID != "m2" || got.ThreadID != "t1" {
+		t.Fatalf("upsert keep thread = %+v, %v", got, err)
+	}
+	if _, err := links.GetByMessageID(ctx, "m2"); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := links.GetRootByThreadID(ctx, "t1"); err != nil {
+		t.Fatal(err)
+	}
+}

internal/discord/format.go

@@ -0,0 +1,111 @@
+package discord
+
+import (
+	"strings"
+
+	"plumber/internal/events"
+)
+
+const (
+	embedTitleLimit       = 256
+	embedDescriptionLimit = 4096
+	threadNameLimit       = 100
+	embedColor            = 0xe96a26
+)
+
+// Message is a Discord-ready snapshot of a site post event.
+type Message struct {
+	Title       string
+	URL         string
+	Description string
+	City        string
+	Author      string
+	ImageURLs   []string
+	ThreadName  string
+}
+
+func formatMessage(ev events.PostEvent) Message {
+	title := strings.TrimSpace(ev.Title)
+	if title == "" {
+		title = "Reply"
+	}
+	author := strings.TrimSpace(ev.AuthorName)
+	if author == "" {
+		author = "Someone"
+	}
+	msg := Message{
+		Title:       truncateRunes(title, embedTitleLimit),
+		URL:         strings.TrimSpace(ev.Permalink),
+		Description: truncateRunes(strings.TrimSpace(ev.Body), embedDescriptionLimit),
+		City:        strings.TrimSpace(ev.City),
+		Author:      author,
+		ThreadName:  threadName(author, ev.Title),
+	}
+	for _, img := range ev.Images {
+		url := strings.TrimSpace(img.URL)
+		if url == "" {
+			continue
+		}
+		msg.ImageURLs = append(msg.ImageURLs, url)
+	}
+	return msg
+}
+
+func threadName(author, title string) string {
+	author = strings.TrimSpace(author)
+	if author == "" {
+		author = "Someone"
+	}
+	title = strings.TrimSpace(title)
+	if title == "" {
+		title = "Question"
+	}
+	return truncateRunes(author+" asks: "+title, threadNameLimit)
+}
+
+func truncateRunes(s string, max int) string {
+	if max <= 0 {
+		return ""
+	}
+	runes := []rune(s)
+	if len(runes) <= max {
+		return s
+	}
+	return string(runes[:max])
+}
+
+func isRoot(ev events.PostEvent) bool {
+	return strings.TrimSpace(ev.ParentID) == ""
+}
+
+func messageContent(msg Message) string {
+	var parts []string
+	if body := strings.TrimSpace(msg.Description); body != "" {
+		parts = append(parts, body)
+	}
+	var meta []string
+	if msg.City != "" {
+		meta = append(meta, msg.City)
+	}
+	if msg.Author != "" {
+		meta = append(meta, msg.Author)
+	}
+	if len(meta) > 0 {
+		parts = append(parts, strings.Join(meta, " · "))
+	}
+	if u := publicURL(msg.URL); u != "" {
+		parts = append(parts, u)
+	}
+	return truncateRunes(strings.Join(parts, "\n"), 2000)
+}
+
+func publicURL(raw string) string {
+	raw = strings.TrimSpace(raw)
+	if !strings.HasPrefix(raw, "https://") {
+		return ""
+	}
+	if strings.Contains(raw, "localhost") || strings.Contains(raw, "127.0.0.1") {
+		return ""
+	}
+	return raw
+}

internal/discord/inbound.go

@@ -0,0 +1,203 @@
+package discord
+
+import (
+	"context"
+	"database/sql"
+	"errors"
+	"fmt"
+	"log"
+	"strings"
+
+	"github.com/bwmarrin/discordgo"
+
+	"plumber/internal/events"
+	"plumber/internal/store"
+)
+
+const inboundBodyLimit = 12000
+
+type inboundMessage struct {
+	ID                  string
+	ChannelID           string
+	GuildID             string
+	AuthorID            string
+	Content             string
+	ReferencedMessageID string
+	Bot                 bool
+	Attachments         int
+}
+
+func parseAdminMap(raw string) map[string]string {
+	out := map[string]string{}
+	for _, part := range strings.Split(raw, ",") {
+		part = strings.TrimSpace(part)
+		if part == "" {
+			continue
+		}
+		id, username, ok := strings.Cut(part, ":")
+		id = strings.TrimSpace(id)
+		username = store.NormalizeUsername(username)
+		if !ok || id == "" || username == "" {
+			log.Printf("discord: skip invalid DISCORD_ADMIN_MAP entry %q", part)
+			continue
+		}
+		out[id] = username
+	}
+	return out
+}
+
+func (b *Bot) onMessageCreate(_ *discordgo.Session, m *discordgo.MessageCreate) {
+	if b == nil || m == nil || m.Author == nil {
+		return
+	}
+	in := inboundMessage{
+		ID:          m.ID,
+		ChannelID:   m.ChannelID,
+		GuildID:     m.GuildID,
+		AuthorID:    m.Author.ID,
+		Content:     m.Content,
+		Bot:         m.Author.Bot,
+		Attachments: len(m.Attachments),
+	}
+	if m.MessageReference != nil {
+		in.ReferencedMessageID = m.MessageReference.MessageID
+	}
+	b.handleInbound(in)
+}
+
+func (b *Bot) handleInbound(in inboundMessage) {
+	if b == nil || b.store == nil {
+		return
+	}
+	if in.Bot || strings.TrimSpace(in.GuildID) == "" {
+		return
+	}
+	if b.botUserID != "" && in.AuthorID == b.botUserID {
+		return
+	}
+	body := strings.TrimSpace(in.Content)
+	if in.Attachments > 0 {
+		log.Printf("discord: ignoring %d attachment(s) on %s", in.Attachments, in.ID)
+	}
+	if body == "" {
+		return
+	}
+	ctx, cancel := context.WithTimeout(context.Background(), discordTimeout)
+	defer cancel()
+	if !b.knownChannel(ctx, in.ChannelID) {
+		return
+	}
+	username := b.admins[in.AuthorID]
+	if username == "" {
+		return
+	}
+	author, err := b.store.UserByUsername(ctx, username)
+	if err != nil {
+		if !errors.Is(err, sql.ErrNoRows) {
+			log.Printf("discord: inbound author %s: %v", username, err)
+		}
+		return
+	}
+	if !author.Admin() {
+		log.Printf("discord: inbound %s is not an admin", username)
+		return
+	}
+	parent, root, err := b.inboundParent(ctx, in)
+	if err != nil {
+		if !errors.Is(err, sql.ErrNoRows) {
+			log.Printf("discord: inbound parent %s: %v", in.ID, err)
+		}
+		return
+	}
+	if root.PostState == store.PostStateHidden {
+		return
+	}
+	reply := &store.Post{
+		AuthorID: author.ID,
+		Body:     truncateRunes(body, inboundBodyLimit),
+		ParentID: &parent.ID,
+	}
+	if err := b.store.CreatePost(ctx, reply); err != nil {
+		log.Printf("discord: create inbound %s: %v", in.ID, err)
+		return
+	}
+	if err := b.links.Upsert(ctx, store.DiscordLink{
+		PostID:    reply.ID,
+		MessageID: in.ID,
+	}); err != nil {
+		log.Printf("discord: save inbound link %s: %v", reply.ID, err)
+		return
+	}
+	b.publishInbound(reply, root, author)
+	log.Printf("discord: inbound reply %s -> post %s", in.ID, reply.ID)
+}
+
+func (b *Bot) knownChannel(ctx context.Context, channelID string) bool {
+	if strings.TrimSpace(channelID) == "" {
+		return false
+	}
+	if channelID == b.channelID {
+		return true
+	}
+	_, err := b.links.GetRootByThreadID(ctx, channelID)
+	return err == nil
+}
+
+func (b *Bot) inboundParent(ctx context.Context, in inboundMessage) (*store.Post, *store.Post, error) {
+	if ref := strings.TrimSpace(in.ReferencedMessageID); ref != "" {
+		link, err := b.links.GetByMessageID(ctx, ref)
+		if err == nil {
+			return b.postAndRoot(ctx, link.PostID)
+		}
+		if !errors.Is(err, sql.ErrNoRows) {
+			return nil, nil, err
+		}
+	}
+	link, err := b.links.GetRootByThreadID(ctx, in.ChannelID)
+	if err != nil {
+		return nil, nil, err
+	}
+	return b.postAndRoot(ctx, link.PostID)
+}
+
+func (b *Bot) postAndRoot(ctx context.Context, postID string) (*store.Post, *store.Post, error) {
+	postID = strings.TrimSpace(postID)
+	if postID == "" {
+		return nil, nil, sql.ErrNoRows
+	}
+	post, err := b.store.GetPost(ctx, postID)
+	if err != nil {
+		return nil, nil, err
+	}
+	current := post
+	seen := map[string]bool{}
+	for current.ParentID != nil {
+		if seen[current.ID] {
+			return nil, nil, fmt.Errorf("post ancestry cycle at %s", current.ID)
+		}
+		seen[current.ID] = true
+		current, err = b.store.GetPost(ctx, *current.ParentID)
+		if err != nil {
+			return nil, nil, err
+		}
+	}
+	return post, current, nil
+}
+
+func (b *Bot) publishInbound(reply, root *store.Post, author *store.User) {
+	if b == nil || b.bus == nil || reply == nil || root == nil || author == nil {
+		return
+	}
+	ev := events.PostEvent{
+		PostID:     reply.ID,
+		RootID:     root.ID,
+		Body:       reply.Body,
+		AuthorID:   author.ID,
+		AuthorName: author.Name,
+		AuthorRole: string(author.Role),
+	}
+	if reply.ParentID != nil {
+		ev.ParentID = *reply.ParentID
+	}
+	b.bus.Publish(context.Background(), events.PostCreated{PostEvent: ev})
+}

internal/discord/inbound_test.go

@@ -0,0 +1,219 @@
+package discord
+
+import (
+	"context"
+	"testing"
+	"time"
+
+	"plumber/internal/events"
+	"plumber/internal/mail"
+	"plumber/internal/pacific"
+	"plumber/internal/store"
+)
+
+func TestParseAdminMap(t *testing.T) {
+	t.Parallel()
+
+	got := parseAdminMap(" 123:Plumber ,456:other,bad, :empty,789: ")
+	if got["123"] != "plumber" || got["456"] != "other" || len(got) != 2 {
+		t.Fatalf("parseAdminMap = %#v", got)
+	}
+}
+
+func TestInboundCreatesSiteReply(t *testing.T) {
+	t.Parallel()
+
+	mem, homeowner, admin := seedInboundUsers(t)
+	links := newMemoryLinks()
+	api := &fakeAPI{}
+	mailer := &mail.Recording{}
+	bot := inboundTestBot(mem, links, api, admin.Username)
+	bus := events.New()
+	defer bus.Close()
+	bot.bus = bus
+	mail.Subscribe(bus, mem, mailer)
+	bus.Subscribe(bot.Handle)
+	root := seedLinkedRoot(t, mem, links, homeowner.ID, "thread-1")
+
+	bot.handleInbound(inboundMessage{
+		ID:        "d-reply-1",
+		ChannelID: "thread-1",
+		GuildID:   "guild-1",
+		AuthorID:  "snow-admin",
+		Content:   "Replace the cartridge.",
+	})
+
+	thread, err := mem.GetPostThread(context.Background(), root.ID)
+	if err != nil || len(thread.Replies) != 1 {
+		t.Fatalf("thread = %+v, %v", thread, err)
+	}
+	reply := thread.Replies[0]
+	if reply.AuthorID != admin.ID || reply.Body != "Replace the cartridge." || reply.ParentID == nil || *reply.ParentID != root.ID {
+		t.Fatalf("reply = %+v", reply)
+	}
+	link, err := links.GetByPostID(context.Background(), reply.ID)
+	if err != nil || link.MessageID != "d-reply-1" || link.ThreadID != "" {
+		t.Fatalf("inbound link = %+v, %v", link, err)
+	}
+	time.Sleep(20 * time.Millisecond)
+	if len(api.sends) != 0 || len(api.edits) != 0 {
+		t.Fatalf("inbound echoed to Discord: sends=%+v edits=%+v", api.sends, api.edits)
+	}
+	msgs := waitForMail(t, mailer, 1)
+	if msgs[0].ToEmail != homeowner.Email || msgs[0].ReplyID != reply.ID || msgs[0].RootID != root.ID {
+		t.Fatalf("mail = %+v", msgs[0])
+	}
+}
+
+func TestInboundParentsFromReference(t *testing.T) {
+	t.Parallel()
+
+	mem, homeowner, admin := seedInboundUsers(t)
+	links := newMemoryLinks()
+	bot := inboundTestBot(mem, links, &fakeAPI{}, admin.Username)
+	root := seedLinkedRoot(t, mem, links, homeowner.ID, "thread-1")
+	plumberReply := &store.Post{ParentID: &root.ID, AuthorID: admin.ID, Body: "First look."}
+	if err := mem.CreatePost(context.Background(), plumberReply); err != nil {
+		t.Fatal(err)
+	}
+	if err := links.Upsert(context.Background(), store.DiscordLink{
+		PostID:    plumberReply.ID,
+		MessageID: "d-plumber-1",
+	}); err != nil {
+		t.Fatal(err)
+	}
+
+	bot.handleInbound(inboundMessage{
+		ID:                  "d-nested",
+		ChannelID:           "thread-1",
+		GuildID:             "guild-1",
+		AuthorID:            "snow-admin",
+		Content:             "More detail.",
+		ReferencedMessageID: "d-plumber-1",
+	})
+
+	thread, err := mem.GetPostThread(context.Background(), root.ID)
+	if err != nil || len(thread.Replies) != 1 || len(thread.Replies[0].Replies) != 1 {
+		t.Fatalf("thread = %+v, %v", thread, err)
+	}
+	nested := thread.Replies[0].Replies[0]
+	if nested.ParentID == nil || *nested.ParentID != plumberReply.ID {
+		t.Fatalf("nested parent = %+v", nested)
+	}
+}
+
+func TestInboundIgnoresAllowlistHiddenAndEchoSources(t *testing.T) {
+	t.Parallel()
+
+	mem, homeowner, admin := seedInboundUsers(t)
+	links := newMemoryLinks()
+	api := &fakeAPI{}
+	bot := inboundTestBot(mem, links, api, admin.Username)
+	root := seedLinkedRoot(t, mem, links, homeowner.ID, "thread-1")
+	hidden := &store.Post{
+		AuthorID:  homeowner.ID,
+		Title:     "Hidden",
+		Body:      "No.",
+		PostDate:  pacific.Today(),
+		PostState: store.PostStateHidden,
+	}
+	if err := mem.CreatePost(context.Background(), hidden); err != nil {
+		t.Fatal(err)
+	}
+	if err := links.Upsert(context.Background(), store.DiscordLink{
+		PostID:    hidden.ID,
+		MessageID: "d-hidden",
+		ThreadID:  "thread-hidden",
+	}); err != nil {
+		t.Fatal(err)
+	}
+
+	cases := []inboundMessage{
+		{ID: "bot", ChannelID: "thread-1", GuildID: "g", AuthorID: "snow-admin", Content: "x", Bot: true},
+		{ID: "dm", ChannelID: "thread-1", AuthorID: "snow-admin", Content: "x"},
+		{ID: "self", ChannelID: "thread-1", GuildID: "g", AuthorID: "bot-1", Content: "x"},
+		{ID: "stranger", ChannelID: "thread-1", GuildID: "g", AuthorID: "snow-other", Content: "x"},
+		{ID: "elsewhere", ChannelID: "other-thread", GuildID: "g", AuthorID: "snow-admin", Content: "x"},
+		{ID: "empty", ChannelID: "thread-1", GuildID: "g", AuthorID: "snow-admin", Content: "   ", Attachments: 1},
+		{ID: "hidden", ChannelID: "thread-hidden", GuildID: "g", AuthorID: "snow-admin", Content: "x"},
+		{ID: "channel-root", ChannelID: "channel-1", GuildID: "g", AuthorID: "snow-admin", Content: "new question"},
+	}
+	for _, in := range cases {
+		bot.handleInbound(in)
+	}
+	thread, err := mem.GetPostThread(context.Background(), root.ID)
+	if err != nil || len(thread.Replies) != 0 {
+		t.Fatalf("unexpected replies: %+v, %v", thread, err)
+	}
+	if len(api.sends) != 0 {
+		t.Fatalf("unexpected discord sends %+v", api.sends)
+	}
+}
+
+func inboundTestBot(mem *store.Memory, links *memoryLinks, api *fakeAPI, adminUsername string) *Bot {
+	bot := New("channel-1", links, api)
+	bot.store = mem
+	bot.admins = map[string]string{"snow-admin": adminUsername}
+	bot.botUserID = "bot-1"
+	return bot
+}
+
+func seedInboundUsers(t *testing.T) (*store.Memory, *store.User, *store.User) {
+	t.Helper()
+	mem := store.NewMemory()
+	homeowner := &store.User{
+		Username:     "homeowner",
+		Name:         "Sam",
+		Email:        "sam@example.com",
+		PasswordHash: "x",
+		Role:         store.RoleUser,
+	}
+	if err := mem.CreateUser(context.Background(), homeowner); err != nil {
+		t.Fatal(err)
+	}
+	admin := &store.User{
+		Username:     "plumber",
+		Name:         "Pat",
+		Email:        "pat@example.com",
+		PasswordHash: "x",
+		Role:         store.RoleAdmin,
+	}
+	if err := mem.CreateUser(context.Background(), admin); err != nil {
+		t.Fatal(err)
+	}
+	return mem, homeowner, admin
+}
+
+func seedLinkedRoot(t *testing.T, mem *store.Memory, links *memoryLinks, authorID, threadID string) *store.Post {
+	t.Helper()
+	root := &store.Post{
+		AuthorID: authorID,
+		Title:    "Leaky sink",
+		Body:     "It drips.",
+		PostDate: pacific.Today(),
+	}
+	if err := mem.CreatePost(context.Background(), root); err != nil {
+		t.Fatal(err)
+	}
+	if err := links.Upsert(context.Background(), store.DiscordLink{
+		PostID:    root.ID,
+		MessageID: "d-root",
+		ThreadID:  threadID,
+	}); err != nil {
+		t.Fatal(err)
+	}
+	return root
+}
+
+func waitForMail(t *testing.T, recording *mail.Recording, want int) []mail.PostReply {
+	t.Helper()
+	deadline := time.Now().Add(2 * time.Second)
+	for time.Now().Before(deadline) {
+		if recording.Len() >= want {
+			return recording.Snapshot()
+		}
+		time.Sleep(10 * time.Millisecond)
+	}
+	t.Fatalf("recorded %d notifications, want %d", recording.Len(), want)
+	return nil
+}

internal/discord/memory_links.go

@@ -0,0 +1,88 @@
+package discord
+
+import (
+	"context"
+	"database/sql"
+	"strings"
+	"sync"
+	"time"
+
+	"plumber/internal/store"
+)
+
+// memoryLinks is an in-process DiscordLinkStore for tests.
+type memoryLinks struct {
+	mu        sync.Mutex
+	byPost    map[string]store.DiscordLink
+	byMessage map[string]string
+	byThread  map[string]string
+}
+
+func newMemoryLinks() *memoryLinks {
+	return &memoryLinks{
+		byPost:    map[string]store.DiscordLink{},
+		byMessage: map[string]string{},
+		byThread:  map[string]string{},
+	}
+}
+
+func (m *memoryLinks) GetByPostID(_ context.Context, postID string) (*store.DiscordLink, error) {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	link, ok := m.byPost[strings.TrimSpace(postID)]
+	if !ok {
+		return nil, sql.ErrNoRows
+	}
+	cp := link
+	return &cp, nil
+}
+
+func (m *memoryLinks) GetByMessageID(_ context.Context, messageID string) (*store.DiscordLink, error) {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	postID, ok := m.byMessage[strings.TrimSpace(messageID)]
+	if !ok {
+		return nil, sql.ErrNoRows
+	}
+	link := m.byPost[postID]
+	cp := link
+	return &cp, nil
+}
+
+func (m *memoryLinks) GetRootByThreadID(_ context.Context, threadID string) (*store.DiscordLink, error) {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	postID, ok := m.byThread[strings.TrimSpace(threadID)]
+	if !ok {
+		return nil, sql.ErrNoRows
+	}
+	link := m.byPost[postID]
+	cp := link
+	return &cp, nil
+}
+
+func (m *memoryLinks) Upsert(_ context.Context, link store.DiscordLink) error {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	link.PostID = strings.TrimSpace(link.PostID)
+	link.MessageID = strings.TrimSpace(link.MessageID)
+	link.ThreadID = strings.TrimSpace(link.ThreadID)
+	if link.CreatedAt == "" {
+		link.CreatedAt = time.Now().UTC().Format(time.RFC3339Nano)
+	}
+	if prev, ok := m.byPost[link.PostID]; ok {
+		delete(m.byMessage, prev.MessageID)
+		if prev.ThreadID != "" {
+			delete(m.byThread, prev.ThreadID)
+		}
+		if link.ThreadID == "" {
+			link.ThreadID = prev.ThreadID
+		}
+	}
+	m.byPost[link.PostID] = link
+	m.byMessage[link.MessageID] = link.PostID
+	if link.ThreadID != "" {
+		m.byThread[link.ThreadID] = link.PostID
+	}
+	return nil
+}

internal/events/bus.go

@@ -0,0 +1,79 @@
+package events
+
+import (
+	"context"
+	"log"
+	"sync"
+)
+
+const defaultBuffer = 64
+
+// Publisher is the site-facing write side of the bus.
+type Publisher interface {
+	Publish(ctx context.Context, ev any)
+}
+
+// Bus is an in-process pub/sub with one worker and a bounded queue.
+type Bus struct {
+	ch     chan any
+	mu     sync.Mutex
+	subs   []func(context.Context, any)
+	closed sync.Once
+}
+
+// New starts a worker that delivers events to subscribers in publish order.
+func New() *Bus {
+	return newBus(defaultBuffer, true)
+}
+
+func newBus(buffer int, start bool) *Bus {
+	if buffer < 1 {
+		buffer = 1
+	}
+	b := &Bus{ch: make(chan any, buffer)}
+	if start {
+		go b.loop()
+	}
+	return b
+}
+
+// Publish enqueues ev. It never blocks the caller; a full buffer is dropped.
+func (b *Bus) Publish(_ context.Context, ev any) {
+	if b == nil {
+		return
+	}
+	select {
+	case b.ch <- ev:
+	default:
+		log.Printf("events: dropped %T", ev)
+	}
+}
+
+// Subscribe adds a handler. Handlers run serially on the worker.
+func (b *Bus) Subscribe(fn func(context.Context, any)) {
+	if b == nil || fn == nil {
+		return
+	}
+	b.mu.Lock()
+	b.subs = append(b.subs, fn)
+	b.mu.Unlock()
+}
+
+func (b *Bus) loop() {
+	for ev := range b.ch {
+		b.mu.Lock()
+		subs := append([]func(context.Context, any){}, b.subs...)
+		b.mu.Unlock()
+		for _, fn := range subs {
+			fn(context.Background(), ev)
+		}
+	}
+}
+
+// Close stops the worker. Safe to call more than once.
+func (b *Bus) Close() {
+	if b == nil {
+		return
+	}
+	b.closed.Do(func() { close(b.ch) })
+}

internal/events/bus_test.go

@@ -0,0 +1,104 @@
+package events
+
+import (
+	"context"
+	"sync"
+	"testing"
+	"time"
+)
+
+func TestPermalink(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		base, root, post, want string
+	}{
+		{"", "root-1", "post-2", "/questions/root-1#post-post-2"},
+		{"https://www.askaplumberfirst.com/", "root-1", "post-2", "https://www.askaplumberfirst.com/questions/root-1#post-post-2"},
+		{"https://www.askaplumberfirst.com", "a b", "c/d", "https://www.askaplumberfirst.com/questions/a%20b#post-c%2Fd"},
+	}
+	for _, tc := range tests {
+		if got := Permalink(tc.base, tc.root, tc.post); got != tc.want {
+			t.Fatalf("Permalink(%q, %q, %q) = %q, want %q", tc.base, tc.root, tc.post, got, tc.want)
+		}
+	}
+}
+
+func TestNopAndRecording(t *testing.T) {
+	t.Parallel()
+
+	Nop{}.Publish(context.Background(), PostCreated{})
+
+	rec := &Recording{}
+	rec.Publish(context.Background(), PostCreated{PostEvent: PostEvent{PostID: "a"}})
+	rec.Publish(context.Background(), PostUpdated{PostEvent: PostEvent{PostID: "b"}})
+	if rec.Len() != 2 {
+		t.Fatalf("len = %d", rec.Len())
+	}
+	got := rec.Snapshot()
+	created, ok := got[0].(PostCreated)
+	if !ok || created.PostID != "a" {
+		t.Fatalf("first = %#v", got[0])
+	}
+	updated, ok := got[1].(PostUpdated)
+	if !ok || updated.PostID != "b" {
+		t.Fatalf("second = %#v", got[1])
+	}
+}
+
+func TestBusDeliversInOrder(t *testing.T) {
+	t.Parallel()
+
+	bus := New()
+	defer bus.Close()
+
+	var mu sync.Mutex
+	var got []string
+	done := make(chan struct{})
+	bus.Subscribe(func(_ context.Context, ev any) {
+		mu.Lock()
+		got = append(got, ev.(string))
+		if len(got) == 3 {
+			close(done)
+		}
+		mu.Unlock()
+	})
+
+	ctx := context.Background()
+	bus.Publish(ctx, "one")
+	bus.Publish(ctx, "two")
+	bus.Publish(ctx, "three")
+
+	select {
+	case <-done:
+	case <-time.After(time.Second):
+		t.Fatal("timed out waiting for events")
+	}
+	mu.Lock()
+	defer mu.Unlock()
+	if len(got) != 3 || got[0] != "one" || got[1] != "two" || got[2] != "three" {
+		t.Fatalf("got %v", got)
+	}
+}
+
+func TestBusDropsWhenFull(t *testing.T) {
+	t.Parallel()
+
+	bus := newBus(1, false)
+	bus.Publish(context.Background(), "kept")
+	bus.Publish(context.Background(), "dropped")
+
+	select {
+	case ev := <-bus.ch:
+		if ev != "kept" {
+			t.Fatalf("got %v", ev)
+		}
+	default:
+		t.Fatal("expected buffered event")
+	}
+	select {
+	case ev := <-bus.ch:
+		t.Fatalf("unexpected extra event %v", ev)
+	default:
+	}
+}

internal/events/event.go

@@ -0,0 +1,47 @@
+package events
+
+import (
+	"net/url"
+	"strings"
+)
+
+// Image is a public photo already attached to a site post.
+type Image struct {
+	URL         string
+	Description string
+}
+
+// PostEvent is a Discord-free snapshot of a site post after a successful write.
+type PostEvent struct {
+	PostID     string
+	RootID     string
+	ParentID   string
+	Title      string
+	Body       string
+	City       string
+	AuthorID   string
+	AuthorName string
+	AuthorRole string
+	Images     []Image
+	Permalink  string
+}
+
+// PostCreated is emitted after a successful site create.
+type PostCreated struct {
+	PostEvent
+}
+
+// PostUpdated is emitted after a successful site edit.
+type PostUpdated struct {
+	PostEvent
+}
+
+// Permalink builds /questions/{root}#post-{id}, prefixed by baseURL when set.
+func Permalink(baseURL, rootID, postID string) string {
+	path := "/questions/" + url.PathEscape(rootID) + "#post-" + url.PathEscape(postID)
+	base := strings.TrimRight(strings.TrimSpace(baseURL), "/")
+	if base == "" {
+		return path
+	}
+	return base + path
+}

internal/events/nop.go

@@ -0,0 +1,9 @@
+package events
+
+import "context"
+
+// Nop is a Publisher used when nothing is subscribed.
+type Nop struct{}
+
+// Publish discards ev.
+func (Nop) Publish(context.Context, any) {}

internal/events/recording.go

@@ -0,0 +1,44 @@
+package events
+
+import (
+	"context"
+	"sync"
+)
+
+// Recording is a test Publisher that records events synchronously.
+type Recording struct {
+	mu  sync.Mutex
+	evs []any
+}
+
+// Publish appends ev.
+func (r *Recording) Publish(_ context.Context, ev any) {
+	if r == nil {
+		return
+	}
+	r.mu.Lock()
+	defer r.mu.Unlock()
+	r.evs = append(r.evs, ev)
+}
+
+// Len returns the number of recorded events.
+func (r *Recording) Len() int {
+	if r == nil {
+		return 0
+	}
+	r.mu.Lock()
+	defer r.mu.Unlock()
+	return len(r.evs)
+}
+
+// Snapshot returns a copy of recorded events.
+func (r *Recording) Snapshot() []any {
+	if r == nil {
+		return nil
+	}
+	r.mu.Lock()
+	defer r.mu.Unlock()
+	out := make([]any, len(r.evs))
+	copy(out, r.evs)
+	return out
+}

internal/mail/subscriber.go

@@ -0,0 +1,89 @@
+package mail
+
+import (
+	"context"
+	"log"
+	"strings"
+	"time"
+
+	"plumber/internal/events"
+	"plumber/internal/store"
+)
+
+// Subscribe sends reply emails from PostCreated events. Nop or nil is a no-op.
+func Subscribe(bus *events.Bus, st store.Store, n Notifier) {
+	if bus == nil || st == nil || n == nil {
+		return
+	}
+	if _, disabled := n.(Nop); disabled {
+		return
+	}
+	s := subscriber{store: st, mail: n}
+	bus.Subscribe(s.handle)
+}
+
+type subscriber struct {
+	store store.Store
+	mail  Notifier
+}
+
+func (s subscriber) handle(_ context.Context, ev any) {
+	created, ok := ev.(events.PostCreated)
+	if !ok {
+		return
+	}
+	if strings.TrimSpace(created.ParentID) == "" {
+		return
+	}
+	go s.notifyReply(created.PostEvent)
+}
+
+func (s subscriber) notifyReply(ev events.PostEvent) {
+	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
+	defer cancel()
+
+	parent, err := s.store.GetPost(ctx, ev.ParentID)
+	if err != nil {
+		log.Printf("notify reply %s: load parent: %v", ev.PostID, err)
+		return
+	}
+	root, err := s.store.GetPost(ctx, ev.RootID)
+	if err != nil {
+		log.Printf("notify reply %s: load root: %v", ev.PostID, err)
+		return
+	}
+	author, err := s.store.UserByID(ctx, ev.AuthorID)
+	if err != nil {
+		log.Printf("notify reply %s: load author: %v", ev.PostID, err)
+		return
+	}
+	recipientID := parent.AuthorID
+	if author.Admin() {
+		recipientID = root.AuthorID
+	}
+	if recipientID == author.ID {
+		return
+	}
+	msg := PostReply{
+		RootID:          root.ID,
+		RootTitle:       root.Title,
+		ReplyID:         ev.PostID,
+		ReplyBody:       ev.Body,
+		ReplyAuthorName: author.Name,
+	}
+	recipient, err := s.store.UserByID(ctx, recipientID)
+	if err != nil {
+		log.Printf("notify reply %s: load recipient: %v", msg.ReplyID, err)
+		return
+	}
+	if recipient == nil || strings.TrimSpace(recipient.Email) == "" {
+		return
+	}
+	msg.ToEmail = recipient.Email
+	msg.ToName = recipient.Name
+	if err := s.mail.NotifyPostReply(ctx, msg); err != nil {
+		log.Printf("notify reply %s: %v", msg.ReplyID, err)
+		return
+	}
+	log.Printf("notify reply %s: accepted", msg.ReplyID)
+}

internal/mail/subscriber_test.go

@@ -0,0 +1,200 @@
+package mail
+
+import (
+	"context"
+	"testing"
+	"time"
+
+	"plumber/internal/events"
+	"plumber/internal/pacific"
+	"plumber/internal/store"
+)
+
+func TestSubscribeReplyNotifications(t *testing.T) {
+	t.Parallel()
+
+	mem := store.NewMemory()
+	homeowner := seedMailUser(t, mem, "homeowner", store.RoleUser, "sam@example.com")
+	admin := seedMailUser(t, mem, "plumber", store.RoleAdmin, "pat@example.com")
+	root := seedMailRoot(t, mem, homeowner.ID, "Leaky sink", "It drips.")
+	adminReply := seedMailReply(t, mem, admin.ID, root.ID)
+	homeownerReply := seedMailReply(t, mem, homeowner.ID, adminReply.ID)
+
+	bus := events.New()
+	defer bus.Close()
+	recording := &Recording{}
+	Subscribe(bus, mem, recording)
+
+	ctx := context.Background()
+	bus.Publish(ctx, events.PostCreated{PostEvent: events.PostEvent{
+		PostID:   root.ID,
+		RootID:   root.ID,
+		Title:    root.Title,
+		Body:     root.Body,
+		AuthorID: homeowner.ID,
+	}})
+	bus.Publish(ctx, events.PostUpdated{PostEvent: events.PostEvent{
+		PostID:   adminReply.ID,
+		RootID:   root.ID,
+		ParentID: root.ID,
+		Body:     "Edited",
+		AuthorID: admin.ID,
+	}})
+
+	bus.Publish(ctx, events.PostCreated{PostEvent: events.PostEvent{
+		PostID:   adminReply.ID,
+		RootID:   root.ID,
+		ParentID: root.ID,
+		Body:     adminReply.Body,
+		AuthorID: admin.ID,
+	}})
+	msgs := waitForMail(t, recording, 1)
+	if msg := msgs[0]; msg.ToEmail != homeowner.Email ||
+		msg.RootID != root.ID ||
+		msg.RootTitle != root.Title ||
+		msg.ReplyID != adminReply.ID ||
+		msg.ReplyBody != adminReply.Body ||
+		msg.ReplyAuthorName != admin.Name {
+		t.Fatalf("admin reply = %+v", msg)
+	}
+
+	bus.Publish(ctx, events.PostCreated{PostEvent: events.PostEvent{
+		PostID:   homeownerReply.ID,
+		RootID:   root.ID,
+		ParentID: adminReply.ID,
+		Body:     homeownerReply.Body,
+		AuthorID: homeowner.ID,
+	}})
+	msgs = waitForMail(t, recording, 2)
+	if msg := msgs[1]; msg.ToEmail != admin.Email ||
+		msg.RootID != root.ID ||
+		msg.ReplyID != homeownerReply.ID ||
+		msg.ReplyAuthorName != homeowner.Name {
+		t.Fatalf("homeowner reply = %+v", msg)
+	}
+
+	nestedAdmin := seedMailReply(t, mem, admin.ID, adminReply.ID)
+	bus.Publish(ctx, events.PostCreated{PostEvent: events.PostEvent{
+		PostID:   nestedAdmin.ID,
+		RootID:   root.ID,
+		ParentID: adminReply.ID,
+		Body:     nestedAdmin.Body,
+		AuthorID: admin.ID,
+	}})
+	msgs = waitForMail(t, recording, 3)
+	if msg := msgs[2]; msg.ToEmail != homeowner.Email ||
+		msg.RootID != root.ID ||
+		msg.ReplyBody != nestedAdmin.Body ||
+		msg.ReplyAuthorName != admin.Name {
+		t.Fatalf("nested admin reply = %+v", msg)
+	}
+
+	self := seedMailReply(t, mem, homeowner.ID, root.ID)
+	bus.Publish(ctx, events.PostCreated{PostEvent: events.PostEvent{
+		PostID:   self.ID,
+		RootID:   root.ID,
+		ParentID: root.ID,
+		Body:     self.Body,
+		AuthorID: homeowner.ID,
+	}})
+
+	noEmail := seedMailUser(t, mem, "quiet", store.RoleUser, "")
+	quietRoot := seedMailRoot(t, mem, noEmail.ID, "Quiet thread", "No email.")
+	quietReply := seedMailReply(t, mem, admin.ID, quietRoot.ID)
+	bus.Publish(ctx, events.PostCreated{PostEvent: events.PostEvent{
+		PostID:   quietReply.ID,
+		RootID:   quietRoot.ID,
+		ParentID: quietRoot.ID,
+		Body:     quietReply.Body,
+		AuthorID: admin.ID,
+	}})
+
+	time.Sleep(50 * time.Millisecond)
+	if recording.Len() != 3 {
+		t.Fatalf("self, root, edit, or no-email sent mail: %+v", recording.Snapshot())
+	}
+}
+
+func TestSubscribeNopIgnoresReplies(t *testing.T) {
+	t.Parallel()
+
+	mem := store.NewMemory()
+	homeowner := seedMailUser(t, mem, "homeowner", store.RoleUser, "sam@example.com")
+	admin := seedMailUser(t, mem, "plumber", store.RoleAdmin, "pat@example.com")
+	root := seedMailRoot(t, mem, homeowner.ID, "Leaky sink", "It drips.")
+	reply := seedMailReply(t, mem, admin.ID, root.ID)
+
+	bus := events.New()
+	defer bus.Close()
+	recording := &Recording{}
+	Subscribe(bus, mem, Nop{})
+	Subscribe(nil, mem, recording)
+	Subscribe(bus, mem, nil)
+
+	bus.Publish(context.Background(), events.PostCreated{PostEvent: events.PostEvent{
+		PostID:   reply.ID,
+		RootID:   root.ID,
+		ParentID: root.ID,
+		Body:     reply.Body,
+		AuthorID: admin.ID,
+	}})
+	time.Sleep(50 * time.Millisecond)
+	if recording.Len() != 0 {
+		t.Fatalf("Nop or nil subscribe sent mail: %+v", recording.Snapshot())
+	}
+}
+
+func seedMailUser(t *testing.T, mem *store.Memory, username string, role store.Role, email string) *store.User {
+	t.Helper()
+	u := &store.User{
+		Username:     username,
+		Name:         username,
+		Email:        email,
+		PasswordHash: "x",
+		Role:         role,
+	}
+	if err := mem.CreateUser(context.Background(), u); err != nil {
+		t.Fatal(err)
+	}
+	return u
+}
+
+func seedMailRoot(t *testing.T, mem *store.Memory, authorID, title, body string) *store.Post {
+	t.Helper()
+	root := &store.Post{
+		AuthorID: authorID,
+		Title:    title,
+		Body:     body,
+		PostDate: pacific.Today(),
+	}
+	if err := mem.CreatePost(context.Background(), root); err != nil {
+		t.Fatal(err)
+	}
+	return root
+}
+
+func seedMailReply(t *testing.T, mem *store.Memory, authorID, parentID string) *store.Post {
+	t.Helper()
+	reply := &store.Post{
+		ParentID: &parentID,
+		AuthorID: authorID,
+		Body:     "Reply from " + authorID,
+	}
+	if err := mem.CreatePost(context.Background(), reply); err != nil {
+		t.Fatal(err)
+	}
+	return reply
+}
+
+func waitForMail(t *testing.T, recording *Recording, want int) []PostReply {
+	t.Helper()
+	deadline := time.Now().Add(2 * time.Second)
+	for time.Now().Before(deadline) {
+		if recording.Len() >= want {
+			return recording.Snapshot()
+		}
+		time.Sleep(10 * time.Millisecond)
+	}
+	t.Fatalf("recorded %d notifications, want %d", recording.Len(), want)
+	return nil
+}

internal/store/discord_link.go

@@ -0,0 +1,105 @@
+package store
+
+import (
+	"context"
+	"database/sql"
+	"fmt"
+	"strings"
+	"time"
+
+	"plumber/internal/store/sqlc"
+)
+
+// DiscordLink is the bot-owned mapping from a site post to a Discord message.
+type DiscordLink struct {
+	PostID    string
+	MessageID string
+	ThreadID  string
+	CreatedAt string
+}
+
+// DiscordLinkStore is the mapping table used only by the Discord subscriber.
+// It is not part of Store.
+type DiscordLinkStore interface {
+	GetByPostID(ctx context.Context, postID string) (*DiscordLink, error)
+	GetByMessageID(ctx context.Context, messageID string) (*DiscordLink, error)
+	GetRootByThreadID(ctx context.Context, threadID string) (*DiscordLink, error)
+	Upsert(ctx context.Context, link DiscordLink) error
+}
+
+// DiscordLinks implements DiscordLinkStore against Postgres.
+type DiscordLinks struct {
+	db *sql.DB
+}
+
+// NewDiscordLinks wraps db. It is independent of Store.
+func NewDiscordLinks(db *sql.DB) *DiscordLinks {
+	return &DiscordLinks{db: db}
+}
+
+// GetByPostID returns the link for a site post.
+func (d *DiscordLinks) GetByPostID(ctx context.Context, postID string) (*DiscordLink, error) {
+	if d == nil || d.db == nil {
+		return nil, fmt.Errorf("discord links: no database")
+	}
+	row, err := sqlc.New(d.db).GetDiscordPostLinkByPostID(ctx, strings.TrimSpace(postID))
+	if err != nil {
+		return nil, err
+	}
+	return discordLinkFromRow(row), nil
+}
+
+// GetByMessageID returns the link for a Discord message.
+func (d *DiscordLinks) GetByMessageID(ctx context.Context, messageID string) (*DiscordLink, error) {
+	if d == nil || d.db == nil {
+		return nil, fmt.Errorf("discord links: no database")
+	}
+	row, err := sqlc.New(d.db).GetDiscordPostLinkByMessageID(ctx, strings.TrimSpace(messageID))
+	if err != nil {
+		return nil, err
+	}
+	return discordLinkFromRow(row), nil
+}
+
+// GetRootByThreadID returns the root link for a Discord thread.
+func (d *DiscordLinks) GetRootByThreadID(ctx context.Context, threadID string) (*DiscordLink, error) {
+	if d == nil || d.db == nil {
+		return nil, fmt.Errorf("discord links: no database")
+	}
+	row, err := sqlc.New(d.db).GetDiscordPostLinkByThreadID(ctx, strings.TrimSpace(threadID))
+	if err != nil {
+		return nil, err
+	}
+	return discordLinkFromRow(row), nil
+}
+
+// Upsert inserts or replaces the Discord IDs for a post.
+func (d *DiscordLinks) Upsert(ctx context.Context, link DiscordLink) error {
+	if d == nil || d.db == nil {
+		return fmt.Errorf("discord links: no database")
+	}
+	link.PostID = strings.TrimSpace(link.PostID)
+	link.MessageID = strings.TrimSpace(link.MessageID)
+	link.ThreadID = strings.TrimSpace(link.ThreadID)
+	if link.PostID == "" || link.MessageID == "" {
+		return fmt.Errorf("discord links: post and message ids are required")
+	}
+	if link.CreatedAt == "" {
+		link.CreatedAt = time.Now().UTC().Format(time.RFC3339Nano)
+	}
+	return sqlc.New(d.db).UpsertDiscordPostLink(ctx, sqlc.UpsertDiscordPostLinkParams{
+		PostID:           link.PostID,
+		DiscordMessageID: link.MessageID,
+		DiscordThreadID:  link.ThreadID,
+		CreatedAt:        link.CreatedAt,
+	})
+}
+
+func discordLinkFromRow(row sqlc.DiscordPostLink) *DiscordLink {
+	return &DiscordLink{
+		PostID:    row.PostID,
+		MessageID: row.DiscordMessageID,
+		ThreadID:  row.DiscordThreadID,
+		CreatedAt: row.CreatedAt,
+	}
+}

internal/store/migrate.go

@@ -139,6 +139,51 @@ CREATE TABLE IF NOT EXISTS post_images (
 	return nil
 }
 
+func migrateDiscordPostLinks(ctx context.Context, exec execContext) error {
+	if _, err := exec.ExecContext(ctx, `
+CREATE TABLE IF NOT EXISTS discord_post_links (
+  post_id TEXT PRIMARY KEY REFERENCES posts(id) ON DELETE CASCADE,
+  discord_message_id TEXT NOT NULL UNIQUE,
+  discord_thread_id TEXT NOT NULL DEFAULT '',
+  created_at TEXT NOT NULL
+)`); err != nil {
+		return fmt.Errorf("create discord_post_links: %w", err)
+	}
+	if _, err := exec.ExecContext(ctx, `
+CREATE UNIQUE INDEX IF NOT EXISTS discord_post_links_thread_uidx
+  ON discord_post_links (discord_thread_id)
+  WHERE discord_thread_id <> ''`); err != nil {
+		return fmt.Errorf("discord_post_links_thread_uidx: %w", err)
+	}
+	return nil
+}
+
+func migratePostImageVideo(ctx context.Context, exec execContext) error {
+	steps := []struct {
+		name string
+		sql  string
+	}{
+		{"add kind", `ALTER TABLE post_images ADD COLUMN IF NOT EXISTS kind TEXT NOT NULL DEFAULT 'image'`},
+		{"drop kind check", `ALTER TABLE post_images DROP CONSTRAINT IF EXISTS post_images_kind_check`},
+		{"add kind check", `ALTER TABLE post_images ADD CONSTRAINT post_images_kind_check CHECK (kind IN ('image', 'video'))`},
+		{"drop width check", `ALTER TABLE post_images DROP CONSTRAINT IF EXISTS post_images_width_check`},
+		{"drop height check", `ALTER TABLE post_images DROP CONSTRAINT IF EXISTS post_images_height_check`},
+		{"add width check", `ALTER TABLE post_images ADD CONSTRAINT post_images_width_check CHECK (width >= 0)`},
+		{"add height check", `ALTER TABLE post_images ADD CONSTRAINT post_images_height_check CHECK (height >= 0)`},
+		{"drop image dims check", `ALTER TABLE post_images DROP CONSTRAINT IF EXISTS post_images_image_dims_check`},
+		{"add image dims check", `ALTER TABLE post_images ADD CONSTRAINT post_images_image_dims_check CHECK (kind <> 'image' OR (width > 0 AND height > 0))`},
+		{"drop position check", `ALTER TABLE post_images DROP CONSTRAINT IF EXISTS post_images_position_check`},
+		{"add position check", `ALTER TABLE post_images ADD CONSTRAINT post_images_position_check CHECK (position BETWEEN 0 AND 4)`},
+		{"one video index", `CREATE UNIQUE INDEX IF NOT EXISTS post_images_one_video_uidx ON post_images (post_id) WHERE kind = 'video'`},
+	}
+	for _, step := range steps {
+		if _, err := exec.ExecContext(ctx, step.sql); err != nil {
+			return fmt.Errorf("%s: %w", step.name, err)
+		}
+	}
+	return nil
+}
+
 func migratePostDate(ctx context.Context, exec execContext) error {
 	steps := []struct {
 		name string
@@ -331,6 +376,8 @@ CREATE TABLE IF NOT EXISTS schema_migrations (
 		{"008_post_author_index", migratePostAuthorIndex},
 		{"009_drop_legacy_post_tables", migrateDropLegacyPostTables},
 		{"010_post_images", migratePostImages},
+		{"011_discord_post_links", migrateDiscordPostLinks},
+		{"012_post_image_video", migratePostImageVideo},
 	}
 	for _, m := range migrations {
 		if applied[m.version] {

internal/store/migrate_posts_test.go

@@ -81,6 +81,18 @@ CREATE TABLE users (
 	if err := migratePostImages(ctx, conn); err != nil {
 		t.Fatalf("post images migration is not idempotent: %v", err)
 	}
+	if err := migrateDiscordPostLinks(ctx, conn); err != nil {
+		t.Fatal(err)
+	}
+	if err := migrateDiscordPostLinks(ctx, conn); err != nil {
+		t.Fatalf("discord post links migration is not idempotent: %v", err)
+	}
+	if err := migratePostImageVideo(ctx, conn); err != nil {
+		t.Fatal(err)
+	}
+	if err := migratePostImageVideo(ctx, conn); err != nil {
+		t.Fatalf("post image video migration is not idempotent: %v", err)
+	}
 	if _, err := conn.ExecContext(ctx, `
 INSERT INTO users (id, name, role)
 VALUES ('homeowner', 'Home Owner', 'user'), ('plumber', 'The Plumber', 'admin');
@@ -112,9 +124,9 @@ VALUES ('homeowner', 'root-1', 1);`); err != nil {
 	}
 	imageQueries := sqlc.New(conn)
 	for _, image := range []sqlc.CreatePostImageParams{
-		{ID: "root-image-1", PostID: "root-1", ObjectKey: "posts/root-1/1.jpg", PublicUrl: "https://cdn.example/root-1.jpg", Description: "Valve", Position: 0, Width: 1200, Height: 900, CreatedAt: "2026-08-26T08:00:00Z"},
-		{ID: "root-image-2", PostID: "root-1", ObjectKey: "posts/root-1/2.png", PublicUrl: "https://cdn.example/root-2.png", Position: 1, Width: 900, Height: 1200, CreatedAt: "2026-08-26T08:00:00Z"},
-		{ID: "reply-image-1", PostID: "reply-1", ObjectKey: "posts/reply-1/1.jpg", PublicUrl: "https://cdn.example/reply-1.jpg", Description: "Cartridge", Position: 0, Width: 1000, Height: 1000, CreatedAt: "2026-08-26T09:00:00Z"},
+		{ID: "root-image-1", PostID: "root-1", ObjectKey: "posts/root-1/1.jpg", PublicUrl: "https://cdn.example/root-1.jpg", Description: "Valve", Kind: "image", Position: 0, Width: 1200, Height: 900, CreatedAt: "2026-08-26T08:00:00Z"},
+		{ID: "root-image-2", PostID: "root-1", ObjectKey: "posts/root-1/2.png", PublicUrl: "https://cdn.example/root-2.png", Kind: "image", Position: 1, Width: 900, Height: 1200, CreatedAt: "2026-08-26T08:00:00Z"},
+		{ID: "reply-image-1", PostID: "reply-1", ObjectKey: "posts/reply-1/1.jpg", PublicUrl: "https://cdn.example/reply-1.jpg", Description: "Cartridge", Kind: "image", Position: 0, Width: 1000, Height: 1000, CreatedAt: "2026-08-26T09:00:00Z"},
 	} {
 		if err := imageQueries.CreatePostImage(ctx, image); err != nil {
 			t.Fatal(err)
@@ -138,10 +150,60 @@ VALUES ('homeowner', 'root-1', 1);`); err != nil {
 	}
 	if err := imageQueries.CreatePostImage(ctx, sqlc.CreatePostImageParams{
 		ID: "too-many", PostID: "root-1", ObjectKey: "posts/root-1/5.jpg",
-		PublicUrl: "https://cdn.example/root-5.jpg", Position: 4,
+		PublicUrl: "https://cdn.example/root-5.jpg", Kind: "image", Position: 5,
 		Width: 100, Height: 100, CreatedAt: "2026-08-26T08:00:00Z",
 	}); err == nil {
-		t.Fatal("fifth image position unexpectedly succeeded")
+		t.Fatal("position 5 unexpectedly succeeded")
+	}
+	if err := imageQueries.CreatePostImage(ctx, sqlc.CreatePostImageParams{
+		ID: "root-video-1", PostID: "root-1", ObjectKey: "posts/root-1/clip.mp4",
+		PublicUrl: "https://cdn.example/clip.mp4", Kind: "video", Position: 2,
+		Width: 0, Height: 0, CreatedAt: "2026-08-26T08:00:00Z",
+	}); err != nil {
+		t.Fatal(err)
+	}
+	if err := imageQueries.CreatePostImage(ctx, sqlc.CreatePostImageParams{
+		ID: "root-video-2", PostID: "root-1", ObjectKey: "posts/root-1/clip-2.mp4",
+		PublicUrl: "https://cdn.example/clip-2.mp4", Kind: "video", Position: 3,
+		Width: 0, Height: 0, CreatedAt: "2026-08-26T08:00:00Z",
+	}); err == nil {
+		t.Fatal("second video unexpectedly succeeded")
+	}
+	if err := imageQueries.UpsertDiscordPostLink(ctx, sqlc.UpsertDiscordPostLinkParams{
+		PostID:           "root-1",
+		DiscordMessageID: "msg-root",
+		DiscordThreadID:  "thread-root",
+		CreatedAt:        "2026-08-26T08:00:00Z",
+	}); err != nil {
+		t.Fatal(err)
+	}
+	if err := imageQueries.UpsertDiscordPostLink(ctx, sqlc.UpsertDiscordPostLinkParams{
+		PostID:           "reply-1",
+		DiscordMessageID: "msg-reply",
+		DiscordThreadID:  "",
+		CreatedAt:        "2026-08-26T09:00:00Z",
+	}); err != nil {
+		t.Fatal(err)
+	}
+	rootLink, err := imageQueries.GetDiscordPostLinkByPostID(ctx, "root-1")
+	if err != nil || rootLink.DiscordMessageID != "msg-root" || rootLink.DiscordThreadID != "thread-root" {
+		t.Fatalf("root discord link = %+v, %v", rootLink, err)
+	}
+	threadLink, err := imageQueries.GetDiscordPostLinkByThreadID(ctx, "thread-root")
+	if err != nil || threadLink.PostID != "root-1" {
+		t.Fatalf("thread discord link = %+v, %v", threadLink, err)
+	}
+	if err := imageQueries.UpsertDiscordPostLink(ctx, sqlc.UpsertDiscordPostLinkParams{
+		PostID:           "reply-1",
+		DiscordMessageID: "msg-reply-2",
+		DiscordThreadID:  "",
+		CreatedAt:        "2026-08-26T09:01:00Z",
+	}); err != nil {
+		t.Fatal(err)
+	}
+	replyLink, err := imageQueries.GetDiscordPostLinkByPostID(ctx, "reply-1")
+	if err != nil || replyLink.DiscordMessageID != "msg-reply-2" || replyLink.DiscordThreadID != "" {
+		t.Fatalf("reply upsert = %+v, %v", replyLink, err)
 	}
 	var postVoteIndexCount int
 	if err := conn.QueryRowContext(ctx, `

internal/store/post.go

@@ -29,16 +29,20 @@ const (
 	PostStateHidden          PostState = "hidden"
 	PostStateLocked          PostState = "locked"
 	MaxPostImages                      = 4
+	MaxPostVideos                      = 1
 	MaxImageDescriptionRunes           = 500
+	MediaKindImage                     = "image"
+	MediaKindVideo                     = "video"
 )
 
-// PostImage is one ordered public image attached to a post.
+// PostImage is one ordered public image or video attached to a post.
 type PostImage struct {
 	ID          string
 	PostID      string
 	ObjectKey   string
 	PublicURL   string
 	Description string
+	Kind        string
 	Position    int
 	Width       int
 	Height      int
@@ -200,12 +204,13 @@ func preparePost(p *Post) error {
 }
 
 func preparePostImages(p *Post) error {
-	if len(p.Images) > MaxPostImages {
-		return fmt.Errorf("%w: at most %d images are allowed", ErrInvalidPost, MaxPostImages)
+	if len(p.Images) > MaxPostImages+MaxPostVideos {
+		return fmt.Errorf("%w: at most %d images and %d video are allowed", ErrInvalidPost, MaxPostImages, MaxPostVideos)
 	}
 	ids := make(map[string]bool, len(p.Images))
 	keys := make(map[string]bool, len(p.Images))
 	now := time.Now().UTC().Format(time.RFC3339Nano)
+	images, videos := 0, 0
 	for i := range p.Images {
 		image := &p.Images[i]
 		image.ID = strings.TrimSpace(image.ID)
@@ -213,6 +218,13 @@ func preparePostImages(p *Post) error {
 		image.ObjectKey = strings.TrimSpace(image.ObjectKey)
 		image.PublicURL = strings.TrimSpace(image.PublicURL)
 		image.Description = strings.TrimSpace(image.Description)
+		image.Kind = strings.TrimSpace(image.Kind)
+		if image.Kind == "" {
+			image.Kind = MediaKindImage
+		}
+		if image.Kind != MediaKindImage && image.Kind != MediaKindVideo {
+			return fmt.Errorf("%w: invalid media kind", ErrInvalidPost)
+		}
 		if image.ID == "" {
 			image.ID = uuid.NewString()
 		}
@@ -228,10 +240,19 @@ func preparePostImages(p *Post) error {
 		if len([]rune(image.Description)) > MaxImageDescriptionRunes {
 			return fmt.Errorf("%w: image description is too long", ErrInvalidPost)
 		}
+		if image.Kind == MediaKindImage {
+			images++
 			if image.Width <= 0 || image.Height <= 0 ||
 				image.Width > math.MaxInt32 || image.Height > math.MaxInt32 {
 				return fmt.Errorf("%w: invalid image dimensions", ErrInvalidPost)
 			}
+		} else {
+			videos++
+			if image.Width < 0 || image.Height < 0 ||
+				image.Width > math.MaxInt32 || image.Height > math.MaxInt32 {
+				return fmt.Errorf("%w: invalid video dimensions", ErrInvalidPost)
+			}
+		}
 		if ids[image.ID] || keys[image.ObjectKey] {
 			return fmt.Errorf("%w: duplicate image", ErrInvalidPost)
 		}
@@ -242,6 +263,12 @@ func preparePostImages(p *Post) error {
 			image.CreatedAt = now
 		}
 	}
+	if images > MaxPostImages {
+		return fmt.Errorf("%w: at most %d images are allowed", ErrInvalidPost, MaxPostImages)
+	}
+	if videos > MaxPostVideos {
+		return fmt.Errorf("%w: at most %d video is allowed", ErrInvalidPost, MaxPostVideos)
+	}
 	return nil
 }
 
@@ -253,6 +280,7 @@ func createPostImages(ctx context.Context, q *sqlc.Queries, images []PostImage)
 			ObjectKey:   image.ObjectKey,
 			PublicUrl:   image.PublicURL,
 			Description: image.Description,
+			Kind:        image.Kind,
 			Position:    int16(image.Position),
 			Width:       int32(image.Width),
 			Height:      int32(image.Height),
@@ -271,6 +299,7 @@ func postImageFromSQL(image sqlc.PostImage) PostImage {
 		ObjectKey:   image.ObjectKey,
 		PublicURL:   image.PublicUrl,
 		Description: image.Description,
+		Kind:        image.Kind,
 		Position:    int(image.Position),
 		Width:       int(image.Width),
 		Height:      int(image.Height),

internal/store/post_test.go

@@ -338,6 +338,36 @@ func TestMemoryPostImages(t *testing.T) {
 	if err := mem.CreatePost(ctx, tooMany); !errors.Is(err, ErrInvalidPost) {
 		t.Fatalf("five-image create error = %v, want ErrInvalidPost", err)
 	}
+
+	withVideo := &Post{
+		AuthorID: homeowner.ID,
+		Title:    "With video",
+		Body:     "Four photos and a clip.",
+		Images: append(validPostImages(4), PostImage{
+			ID:        "clip-1",
+			ObjectKey: "posts/clip-1.mp4",
+			PublicURL: "https://cdn.example/clip-1.mp4",
+			Kind:      MediaKindVideo,
+		}),
+	}
+	if err := mem.CreatePost(ctx, withVideo); err != nil {
+		t.Fatalf("four images and one video: %v", err)
+	}
+	if withVideo.Images[4].Kind != MediaKindVideo || withVideo.Images[4].Position != 4 {
+		t.Fatalf("video not stored: %+v", withVideo.Images[4])
+	}
+	twoVideos := &Post{
+		AuthorID: homeowner.ID,
+		Title:    "Two clips",
+		Body:     "Not allowed.",
+		Images: []PostImage{
+			{ObjectKey: "posts/a.mp4", PublicURL: "https://cdn.example/a.mp4", Kind: MediaKindVideo},
+			{ObjectKey: "posts/b.mp4", PublicURL: "https://cdn.example/b.mp4", Kind: MediaKindVideo},
+		},
+	}
+	if err := mem.CreatePost(ctx, twoVideos); !errors.Is(err, ErrInvalidPost) {
+		t.Fatalf("two-video create error = %v, want ErrInvalidPost", err)
+	}
 }
 
 func validPostImages(count int) []PostImage {

internal/store/sqlc/discord_links.sql.go

@@ -0,0 +1,100 @@
+// Code generated by sqlc. DO NOT EDIT.
+// versions:
+//   sqlc v1.31.1
+// source: discord_links.sql
+
+package sqlc
+
+import (
+	"context"
+)
+
+const getDiscordPostLinkByMessageID = `-- name: GetDiscordPostLinkByMessageID :one
+SELECT post_id, discord_message_id, discord_thread_id, created_at
+FROM discord_post_links
+WHERE discord_message_id = $1
+`
+
+func (q *Queries) GetDiscordPostLinkByMessageID(ctx context.Context, discordMessageID string) (DiscordPostLink, error) {
+	row := q.db.QueryRowContext(ctx, getDiscordPostLinkByMessageID, discordMessageID)
+	var i DiscordPostLink
+	err := row.Scan(
+		&i.PostID,
+		&i.DiscordMessageID,
+		&i.DiscordThreadID,
+		&i.CreatedAt,
+	)
+	return i, err
+}
+
+const getDiscordPostLinkByPostID = `-- name: GetDiscordPostLinkByPostID :one
+SELECT post_id, discord_message_id, discord_thread_id, created_at
+FROM discord_post_links
+WHERE post_id = $1
+`
+
+func (q *Queries) GetDiscordPostLinkByPostID(ctx context.Context, postID string) (DiscordPostLink, error) {
+	row := q.db.QueryRowContext(ctx, getDiscordPostLinkByPostID, postID)
+	var i DiscordPostLink
+	err := row.Scan(
+		&i.PostID,
+		&i.DiscordMessageID,
+		&i.DiscordThreadID,
+		&i.CreatedAt,
+	)
+	return i, err
+}
+
+const getDiscordPostLinkByThreadID = `-- name: GetDiscordPostLinkByThreadID :one
+SELECT post_id, discord_message_id, discord_thread_id, created_at
+FROM discord_post_links
+WHERE discord_thread_id = $1
+  AND discord_thread_id <> ''
+`
+
+func (q *Queries) GetDiscordPostLinkByThreadID(ctx context.Context, discordThreadID string) (DiscordPostLink, error) {
+	row := q.db.QueryRowContext(ctx, getDiscordPostLinkByThreadID, discordThreadID)
+	var i DiscordPostLink
+	err := row.Scan(
+		&i.PostID,
+		&i.DiscordMessageID,
+		&i.DiscordThreadID,
+		&i.CreatedAt,
+	)
+	return i, err
+}
+
+const upsertDiscordPostLink = `-- name: UpsertDiscordPostLink :exec
+INSERT INTO discord_post_links (
+  post_id, discord_message_id, discord_thread_id, created_at
+)
+VALUES (
+  $1,
+  $2,
+  $3,
+  $4
+)
+ON CONFLICT (post_id) DO UPDATE SET
+  discord_message_id = EXCLUDED.discord_message_id,
+  discord_thread_id = CASE
+    WHEN EXCLUDED.discord_thread_id <> '' THEN EXCLUDED.discord_thread_id
+    ELSE discord_post_links.discord_thread_id
+  END
+`
+
+type UpsertDiscordPostLinkParams struct {
+	PostID           string
+	DiscordMessageID string
+	DiscordThreadID  string
+	CreatedAt        string
+}
+
+func (q *Queries) UpsertDiscordPostLink(ctx context.Context, arg UpsertDiscordPostLinkParams) error {
+	_, err := q.db.ExecContext(ctx, upsertDiscordPostLink,
+		arg.PostID,
+		arg.DiscordMessageID,
+		arg.DiscordThreadID,
+		arg.CreatedAt,
+	)
+	return err
+}

internal/store/sqlc/models.go

@@ -9,6 +9,13 @@ import (
 	"time"
 )
 
+type DiscordPostLink struct {
+	PostID           string
+	DiscordMessageID string
+	DiscordThreadID  string
+	CreatedAt        string
+}
+
 type Post struct {
 	ID        string
 	ParentID  sql.NullString
@@ -28,6 +35,7 @@ type PostImage struct {
 	ObjectKey   string
 	PublicUrl   string
 	Description string
+	Kind        string
 	Position    int16
 	Width       int32
 	Height      int32

internal/store/sqlc/posts.sql.go

@@ -59,7 +59,7 @@ func (q *Queries) CreatePost(ctx context.Context, arg CreatePostParams) error {
 
 const createPostImage = `-- name: CreatePostImage :exec
 INSERT INTO post_images (
-  id, post_id, object_key, public_url, description, position, width, height, created_at
+  id, post_id, object_key, public_url, description, kind, position, width, height, created_at
 )
 VALUES (
   $1,
@@ -70,7 +70,8 @@ VALUES (
   $6,
   $7,
   $8,
-  $9
+  $9,
+  $10
 )
 `
 
@@ -80,6 +81,7 @@ type CreatePostImageParams struct {
 	ObjectKey   string
 	PublicUrl   string
 	Description string
+	Kind        string
 	Position    int16
 	Width       int32
 	Height      int32
@@ -93,6 +95,7 @@ func (q *Queries) CreatePostImage(ctx context.Context, arg CreatePostImageParams
 		arg.ObjectKey,
 		arg.PublicUrl,
 		arg.Description,
+		arg.Kind,
 		arg.Position,
 		arg.Width,
 		arg.Height,
@@ -201,7 +204,7 @@ func (q *Queries) GetRootPostVoteSummary(ctx context.Context, arg GetRootPostVot
 
 const listPostImages = `-- name: ListPostImages :many
 SELECT
-  id, post_id, object_key, public_url, description, position, width, height, created_at
+  id, post_id, object_key, public_url, description, kind, position, width, height, created_at
 FROM post_images
 WHERE post_id = $1
 ORDER BY position
@@ -222,6 +225,7 @@ func (q *Queries) ListPostImages(ctx context.Context, postID string) ([]PostImag
 			&i.ObjectKey,
 			&i.PublicUrl,
 			&i.Description,
+			&i.Kind,
 			&i.Position,
 			&i.Width,
 			&i.Height,
@@ -327,7 +331,7 @@ WITH RECURSIVE thread AS (
 )
 SELECT
   images.id, images.post_id, images.object_key, images.public_url,
-  images.description, images.position, images.width, images.height, images.created_at
+  images.description, images.kind, images.position, images.width, images.height, images.created_at
 FROM post_images images
 JOIN thread ON thread.id = images.post_id
 ORDER BY images.post_id, images.position
@@ -348,6 +352,7 @@ func (q *Queries) ListPostThreadImages(ctx context.Context, rootID string) ([]Po
 			&i.ObjectKey,
 			&i.PublicUrl,
 			&i.Description,
+			&i.Kind,
 			&i.Position,
 			&i.Width,
 			&i.Height,

internal/web/events.go

@@ -0,0 +1,68 @@
+package web
+
+import (
+	"context"
+
+	"plumber/internal/events"
+	"plumber/internal/store"
+)
+
+func (s *Server) publishPostCreated(post, root *store.Post, author *store.User) {
+	s.publishPost(events.PostCreated{PostEvent: s.postEvent(post, root, author)}, root)
+}
+
+func (s *Server) publishPostUpdated(post, root *store.Post, author *store.User) {
+	s.publishPost(events.PostUpdated{PostEvent: s.postEvent(post, root, author)}, root)
+}
+
+func (s *Server) publishPost(ev any, root *store.Post) {
+	if root != nil && root.PostState == store.PostStateHidden {
+		return
+	}
+	s.cfg.Events.Publish(context.Background(), ev)
+}
+
+func (s *Server) postEvent(post, root *store.Post, author *store.User) events.PostEvent {
+	if post == nil {
+		return events.PostEvent{}
+	}
+	rootID := post.ID
+	if root != nil {
+		rootID = root.ID
+	}
+	ev := events.PostEvent{
+		PostID:     post.ID,
+		RootID:     rootID,
+		Title:      post.Title,
+		Body:       post.Body,
+		City:       post.City,
+		AuthorID:   post.AuthorID,
+		AuthorName: post.AuthorName,
+		AuthorRole: string(post.AuthorRole),
+		Permalink:  events.Permalink(s.cfg.BaseURL, rootID, post.ID),
+	}
+	if post.ParentID != nil {
+		ev.ParentID = *post.ParentID
+	}
+	if author != nil {
+		if ev.AuthorName == "" {
+			ev.AuthorName = author.Name
+		}
+		if ev.AuthorRole == "" {
+			ev.AuthorRole = string(author.Role)
+		}
+	}
+	if n := len(post.Images); n > 0 {
+		ev.Images = make([]events.Image, 0, n)
+		for _, img := range post.Images {
+			if img.Kind == store.MediaKindVideo {
+				continue
+			}
+			ev.Images = append(ev.Images, events.Image{
+				URL:         img.PublicURL,
+				Description: img.Description,
+			})
+		}
+	}
+	return ev
+}

internal/web/events_test.go

@@ -0,0 +1,256 @@
+package web
+
+import (
+	"context"
+	"encoding/json"
+	"net/http"
+	"net/url"
+	"strings"
+	"testing"
+
+	"plumber/internal/events"
+	"plumber/internal/pacific"
+	"plumber/internal/store"
+)
+
+func TestPostHandlersPublishEvents(t *testing.T) {
+	t.Parallel()
+
+	rec := &events.Recording{}
+	srv, mem := newTestServer(t, Config{
+		Events:  rec,
+		BaseURL: "https://www.askaplumberfirst.com",
+	})
+	handler := srv.Handler()
+	homeowner := seedUser(t, mem, uniq("homeowner"), "hunter22", store.RoleUser)
+	admin := seedUser(t, mem, uniq("admin"), "hunter22", store.RoleAdmin)
+	homeownerCookies := loginUser(t, handler, homeowner.Username, "hunter22")
+	adminCookies := loginUser(t, handler, admin.Username, "hunter22")
+	homeownerCSRF := csrfForCookies(t, handler, homeownerCookies)
+	adminCSRF := csrfForCookies(t, handler, adminCookies)
+
+	submit := postForm(handler, "/submit", url.Values{
+		"_csrf": {homeownerCSRF},
+		"title": {"Leaky sink"},
+		"body":  {"Water under the cabinet."},
+		"city":  {"Oakland"},
+	}, homeownerCookies)
+	if submit.Code != http.StatusSeeOther {
+		t.Fatalf("submit status = %d: %s", submit.Code, submit.Body.String())
+	}
+
+	create := postForm(handler, "/posts", url.Values{
+		"_csrf": {homeownerCSRF},
+		"title": {"Second question"},
+		"body":  {"Another leak."},
+		"city":  {"Berkeley"},
+	}, homeownerCookies)
+	if create.Code != http.StatusSeeOther {
+		t.Fatalf("create status = %d: %s", create.Code, create.Body.String())
+	}
+
+	roots, err := mem.ListRootPosts(context.Background(), pacific.Today(), homeowner.ID)
+	if err != nil || len(roots) != 2 {
+		t.Fatalf("roots = %+v, %v", roots, err)
+	}
+	var submitRoot, createRoot store.Post
+	for _, root := range roots {
+		switch root.Title {
+		case "Leaky sink":
+			submitRoot = root
+		case "Second question":
+			createRoot = root
+		}
+	}
+	if submitRoot.ID == "" || createRoot.ID == "" {
+		t.Fatalf("missing created roots: %+v", roots)
+	}
+
+	reply := postForm(handler, "/posts", url.Values{
+		"_csrf":     {adminCSRF},
+		"parent_id": {createRoot.ID},
+		"body":      {"Replace the cartridge."},
+	}, adminCookies)
+	if reply.Code != http.StatusSeeOther {
+		t.Fatalf("reply status = %d: %s", reply.Code, reply.Body.String())
+	}
+	thread, err := mem.GetPostThread(context.Background(), createRoot.ID)
+	if err != nil || len(thread.Replies) != 1 {
+		t.Fatalf("thread = %+v, %v", thread, err)
+	}
+	adminReply := thread.Replies[0]
+
+	edit := postForm(handler, "/posts/"+createRoot.ID+"/edit", url.Values{
+		"_csrf": {homeownerCSRF},
+		"body":  {"Updated leak description."},
+	}, homeownerCookies)
+	if edit.Code != http.StatusSeeOther {
+		t.Fatalf("edit status = %d: %s", edit.Code, edit.Body.String())
+	}
+
+	empty := postForm(handler, "/posts", url.Values{
+		"_csrf": {homeownerCSRF},
+		"title": {"Missing body"},
+	}, homeownerCookies)
+	if empty.Code != http.StatusBadRequest {
+		t.Fatalf("empty body status = %d, want 400", empty.Code)
+	}
+
+	hidden := &store.Post{
+		AuthorID:  homeowner.ID,
+		Title:     "Hidden thread",
+		Body:      "Not public.",
+		PostDate:  pacific.Today(),
+		PostState: store.PostStateHidden,
+	}
+	if err := mem.CreatePost(context.Background(), hidden); err != nil {
+		t.Fatal(err)
+	}
+	hiddenReply := postForm(handler, "/posts", url.Values{
+		"_csrf":     {homeownerCSRF},
+		"parent_id": {hidden.ID},
+		"body":      {"Should not publish."},
+	}, homeownerCookies)
+	if hiddenReply.Code != http.StatusNotFound {
+		t.Fatalf("hidden reply status = %d, want 404", hiddenReply.Code)
+	}
+	hiddenEdit := postForm(handler, "/posts/"+hidden.ID+"/edit", url.Values{
+		"_csrf": {homeownerCSRF},
+		"body":  {"Still hidden."},
+	}, homeownerCookies)
+	if hiddenEdit.Code != http.StatusSeeOther {
+		t.Fatalf("hidden edit status = %d: %s", hiddenEdit.Code, hiddenEdit.Body.String())
+	}
+
+	got := rec.Snapshot()
+	if len(got) != 4 {
+		t.Fatalf("published %d events, want 4: %#v", len(got), got)
+	}
+
+	submitEv, ok := got[0].(events.PostCreated)
+	if !ok {
+		t.Fatalf("first event %T, want PostCreated", got[0])
+	}
+	assertPostEvent(t, submitEv.PostEvent, events.PostEvent{
+		PostID:     submitRoot.ID,
+		RootID:     submitRoot.ID,
+		Title:      "Leaky sink",
+		Body:       "Water under the cabinet.",
+		City:       "Oakland",
+		AuthorID:   homeowner.ID,
+		AuthorName: homeowner.Name,
+		AuthorRole: string(store.RoleUser),
+		Permalink:  "https://www.askaplumberfirst.com/questions/" + submitRoot.ID + "#post-" + submitRoot.ID,
+	})
+
+	createEv, ok := got[1].(events.PostCreated)
+	if !ok {
+		t.Fatalf("second event %T, want PostCreated", got[1])
+	}
+	assertPostEvent(t, createEv.PostEvent, events.PostEvent{
+		PostID:     createRoot.ID,
+		RootID:     createRoot.ID,
+		Title:      "Second question",
+		Body:       "Another leak.",
+		City:       "Berkeley",
+		AuthorID:   homeowner.ID,
+		AuthorName: homeowner.Name,
+		AuthorRole: string(store.RoleUser),
+		Permalink:  "https://www.askaplumberfirst.com/questions/" + createRoot.ID + "#post-" + createRoot.ID,
+	})
+
+	replyEv, ok := got[2].(events.PostCreated)
+	if !ok {
+		t.Fatalf("third event %T, want PostCreated", got[2])
+	}
+	assertPostEvent(t, replyEv.PostEvent, events.PostEvent{
+		PostID:     adminReply.ID,
+		RootID:     createRoot.ID,
+		ParentID:   createRoot.ID,
+		Body:       "Replace the cartridge.",
+		AuthorID:   admin.ID,
+		AuthorName: admin.Name,
+		AuthorRole: string(store.RoleAdmin),
+		Permalink:  "https://www.askaplumberfirst.com/questions/" + createRoot.ID + "#post-" + adminReply.ID,
+	})
+
+	editEv, ok := got[3].(events.PostUpdated)
+	if !ok {
+		t.Fatalf("fourth event %T, want PostUpdated", got[3])
+	}
+	assertPostEvent(t, editEv.PostEvent, events.PostEvent{
+		PostID:     createRoot.ID,
+		RootID:     createRoot.ID,
+		Title:      "Second question",
+		Body:       "Updated leak description.",
+		City:       "Berkeley",
+		AuthorID:   homeowner.ID,
+		AuthorName: homeowner.Name,
+		AuthorRole: string(store.RoleUser),
+		Permalink:  "https://www.askaplumberfirst.com/questions/" + createRoot.ID + "#post-" + createRoot.ID,
+	})
+
+	for i, ev := range got {
+		raw, err := json.Marshal(ev)
+		if err != nil {
+			t.Fatal(err)
+		}
+		if strings.Contains(strings.ToLower(string(raw)), "discord") {
+			t.Fatalf("event %d contains discord fields: %s", i, raw)
+		}
+	}
+}
+
+func TestStoreCreateDoesNotPublish(t *testing.T) {
+	t.Parallel()
+
+	rec := &events.Recording{}
+	_, mem := newTestServer(t, Config{Events: rec})
+	homeowner := seedUser(t, mem, uniq("homeowner"), "hunter22", store.RoleUser)
+	if err := mem.CreatePost(context.Background(), &store.Post{
+		AuthorID: homeowner.ID,
+		Title:    "Direct write",
+		Body:     "No handler.",
+		PostDate: pacific.Today(),
+	}); err != nil {
+		t.Fatal(err)
+	}
+	if rec.Len() != 0 {
+		t.Fatalf("store.CreatePost published %d events", rec.Len())
+	}
+}
+
+func assertPostEvent(t *testing.T, got, want events.PostEvent) {
+	t.Helper()
+	if got.PostID != want.PostID ||
+		got.RootID != want.RootID ||
+		got.ParentID != want.ParentID ||
+		got.Title != want.Title ||
+		got.Body != want.Body ||
+		got.City != want.City ||
+		got.AuthorID != want.AuthorID ||
+		got.AuthorName != want.AuthorName ||
+		got.AuthorRole != want.AuthorRole ||
+		got.Permalink != want.Permalink ||
+		len(got.Images) != 0 {
+		t.Fatalf("event = %+v, want %+v", got, want)
+	}
+}
+
+func TestPostEventOmitsVideos(t *testing.T) {
+	t.Parallel()
+
+	srv, _ := newTestServer(t, Config{})
+	got := srv.postEvent(&store.Post{
+		ID:     "root-1",
+		Title:  "Clip",
+		Body:   "Photo and video.",
+		Images: []store.PostImage{
+			{PublicURL: "https://cdn.example/a.jpg", Description: "Still", Kind: store.MediaKindImage},
+			{PublicURL: "https://cdn.example/a.mp4", Description: "Walkthrough", Kind: store.MediaKindVideo},
+		},
+	}, nil, nil)
+	if len(got.Images) != 1 || got.Images[0].URL != "https://cdn.example/a.jpg" {
+		t.Fatalf("event images = %+v", got.Images)
+	}
+}

internal/web/post_images.go

@@ -28,7 +28,8 @@ import (
 const (
 	defaultRequestBodyBytes  = 3 << 20
 	postImageMaxFileBytes    = 5 << 20
-	postImageMaxRequestBytes = 22 << 20
+	postVideoMaxFileBytes    = 25 << 20
+	postImageMaxRequestBytes = 50 << 20 // 4 images + 1 video + form fields
 	postImageMultipartMemory = 2 << 20
 	postImageMaxSourceDim    = 6000
 	postImageMaxSourcePixels = 16_000_000
@@ -67,7 +68,7 @@ func parsePostMutationForm(w http.ResponseWriter, r *http.Request) (func(), bool
 	contentType := r.Header.Get("Content-Type")
 	mediaType, _, err := mime.ParseMediaType(contentType)
 	if err != nil && strings.HasPrefix(strings.ToLower(contentType), "multipart/") {
-		http.Error(w, "Could not read image upload.", http.StatusBadRequest)
+		http.Error(w, "Could not read upload.", http.StatusBadRequest)
 		return func() {}, false
 	}
 	if mediaType != "multipart/form-data" {
@@ -97,10 +98,10 @@ func writePostImageRequestError(w http.ResponseWriter, err error) {
 	}
 	var maxErr *http.MaxBytesError
 	if errors.As(err, &maxErr) {
-		http.Error(w, "Image upload is too large.", http.StatusRequestEntityTooLarge)
+		http.Error(w, "Upload is too large.", http.StatusRequestEntityTooLarge)
 		return
 	}
-	http.Error(w, "Could not read image upload.", http.StatusBadRequest)
+	http.Error(w, "Could not read upload.", http.StatusBadRequest)
 }
 
 func (s *Server) postImagesFromForm(
@@ -121,9 +122,23 @@ func (s *Server) postImagesFromForm(
 	if len(descriptions) > len(files) {
 		return nil, nil, invalidPostImage("Image descriptions do not match selected images.", nil)
 	}
-	if len(retained)+len(files) > store.MaxPostImages {
+	kinds := make([]string, len(files))
+	newImages, newVideos := 0, 0
+	for i, header := range files {
+		kinds[i] = sniffPostMedia(header)
+		if kinds[i] == store.MediaKindVideo {
+			newVideos++
+		} else {
+			newImages++
+		}
+	}
+	retainedImages, retainedVideos := countPostMedia(retained)
+	if retainedImages+newImages > store.MaxPostImages {
 		return nil, nil, invalidPostImage("You can attach up to 4 images.", nil)
 	}
+	if retainedVideos+newVideos > store.MaxPostVideos {
+		return nil, nil, invalidPostImage("You can attach one video.", nil)
+	}
 	if len(files) > 0 && !s.cfg.Blob.Enabled() {
 		return nil, nil, &postImageRequestError{
 			status:  http.StatusServiceUnavailable,
@@ -142,11 +157,67 @@ func (s *Server) postImagesFromForm(
 			s.deletePostImageObjects(newKeys)
 			return nil, nil, invalidPostImage("Image descriptions must be 500 characters or fewer.", nil)
 		}
-		prepared, err := preparePostImage(header)
+		item, objectKey, err := s.uploadPostMedia(ctx, postID, header, kinds[i], description)
 		if err != nil {
 			s.deletePostImageObjects(newKeys)
 			return nil, nil, err
 		}
+		newKeys = append(newKeys, objectKey)
+		images = append(images, item)
+	}
+	return images, newKeys, nil
+}
+
+func countPostMedia(items []store.PostImage) (images, videos int) {
+	for _, item := range items {
+		if item.Kind == store.MediaKindVideo {
+			videos++
+		} else {
+			images++
+		}
+	}
+	return images, videos
+}
+
+func (s *Server) uploadPostMedia(
+	ctx context.Context,
+	postID string,
+	header *multipart.FileHeader,
+	kind, description string,
+) (store.PostImage, string, error) {
+	if kind == store.MediaKindVideo {
+		prepared, err := preparePostVideo(header)
+		if err != nil {
+			return store.PostImage{}, "", err
+		}
+		mediaID := uuid.NewString()
+		objectKey := path.Join("post-videos", postID, mediaID+prepared.extension)
+		publicURL, err := s.cfg.Blob.Upload(ctx, blob.FileUpload{
+			Key:         objectKey,
+			Body:        bytes.NewReader(prepared.body),
+			ContentType: prepared.contentType,
+			Size:        int64(len(prepared.body)),
+		})
+		if err != nil {
+			return store.PostImage{}, "", &postImageRequestError{
+				status:  http.StatusServiceUnavailable,
+				message: "Could not upload video. Try again later.",
+				cause:   err,
+			}
+		}
+		return store.PostImage{
+			ID:          mediaID,
+			PostID:      postID,
+			ObjectKey:   objectKey,
+			PublicURL:   publicURL,
+			Description: description,
+			Kind:        store.MediaKindVideo,
+		}, objectKey, nil
+	}
+	prepared, err := preparePostImage(header)
+	if err != nil {
+		return store.PostImage{}, "", err
+	}
 	imageID := uuid.NewString()
 	objectKey := path.Join("post-images", postID, imageID+prepared.extension)
 	publicURL, err := s.cfg.Blob.Upload(ctx, blob.FileUpload{
@@ -156,25 +227,22 @@ func (s *Server) postImagesFromForm(
 		Size:        int64(len(prepared.body)),
 	})
 	if err != nil {
-			s.deletePostImageObjects(newKeys)
-			return nil, nil, &postImageRequestError{
+		return store.PostImage{}, "", &postImageRequestError{
 			status:  http.StatusServiceUnavailable,
 			message: "Could not upload image. Try again later.",
 			cause:   err,
 		}
 	}
-		newKeys = append(newKeys, objectKey)
-		images = append(images, store.PostImage{
+	return store.PostImage{
 		ID:          imageID,
 		PostID:      postID,
 		ObjectKey:   objectKey,
 		PublicURL:   publicURL,
 		Description: description,
+		Kind:        store.MediaKindImage,
 		Width:       prepared.width,
 		Height:      prepared.height,
-		})
-	}
-	return images, newKeys, nil
+	}, objectKey, nil
 }
 
 func retainedPostImages(form *multipart.Form, existing []store.PostImage) ([]store.PostImage, error) {
@@ -298,6 +366,94 @@ func preparePostImage(header *multipart.FileHeader) (preparedPostImage, error) {
 	return result, nil
 }
 
+func sniffPostMedia(header *multipart.FileHeader) string {
+	if header == nil {
+		return store.MediaKindImage
+	}
+	file, err := header.Open()
+	if err != nil {
+		return store.MediaKindImage
+	}
+	defer file.Close()
+	peek := make([]byte, 512)
+	n, err := io.ReadFull(file, peek)
+	if err != nil && !errors.Is(err, io.ErrUnexpectedEOF) && !errors.Is(err, io.EOF) {
+		return store.MediaKindImage
+	}
+	return mediaKindFromBytes(peek[:n])
+}
+
+func mediaKindFromBytes(raw []byte) string {
+	switch http.DetectContentType(raw) {
+	case "video/mp4", "video/webm":
+		return store.MediaKindVideo
+	case "image/jpeg", "image/png", "image/webp":
+		return store.MediaKindImage
+	}
+	if isMP4(raw) || isWebM(raw) {
+		return store.MediaKindVideo
+	}
+	return store.MediaKindImage
+}
+
+func isMP4(raw []byte) bool {
+	return len(raw) >= 8 && string(raw[4:8]) == "ftyp"
+}
+
+func isWebM(raw []byte) bool {
+	return len(raw) >= 4 && raw[0] == 0x1a && raw[1] == 0x45 && raw[2] == 0xdf && raw[3] == 0xa3
+}
+
+type preparedPostVideo struct {
+	body        []byte
+	extension   string
+	contentType string
+}
+
+func preparePostVideo(header *multipart.FileHeader) (preparedPostVideo, error) {
+	if header == nil {
+		return preparedPostVideo{}, invalidPostImage("Select a valid video.", nil)
+	}
+	if header.Size > postVideoMaxFileBytes {
+		return preparedPostVideo{}, &postImageRequestError{
+			status:  http.StatusRequestEntityTooLarge,
+			message: "Each video must be 25 MB or smaller.",
+		}
+	}
+	file, err := header.Open()
+	if err != nil {
+		return preparedPostVideo{}, invalidPostImage("Could not read video.", err)
+	}
+	defer file.Close()
+	raw, err := io.ReadAll(io.LimitReader(file, postVideoMaxFileBytes+1))
+	if err != nil {
+		return preparedPostVideo{}, invalidPostImage("Could not read video.", err)
+	}
+	if len(raw) == 0 {
+		return preparedPostVideo{}, invalidPostImage("Videos cannot be empty.", nil)
+	}
+	if int64(len(raw)) > postVideoMaxFileBytes {
+		return preparedPostVideo{}, &postImageRequestError{
+			status:  http.StatusRequestEntityTooLarge,
+			message: "Each video must be 25 MB or smaller.",
+		}
+	}
+	switch mediaKindFromBytes(raw) {
+	case store.MediaKindVideo:
+	default:
+		return preparedPostVideo{}, invalidPostImage("Videos must be MP4 or WebM.", nil)
+	}
+	result := preparedPostVideo{body: raw}
+	if isWebM(raw) {
+		result.extension = ".webm"
+		result.contentType = "video/webm"
+		return result, nil
+	}
+	result.extension = ".mp4"
+	result.contentType = "video/mp4"
+	return result, nil
+}
+
 func jpegOrientation(raw []byte) int {
 	metadata, err := exif.Decode(bytes.NewReader(raw))
 	if err != nil {

internal/web/post_images_test.go

@@ -12,6 +12,7 @@ import (
 	"mime/multipart"
 	"net/http"
 	"net/http/httptest"
+	"strings"
 	"sync"
 	"testing"
 
@@ -56,6 +57,33 @@ func TestPreparePostImage(t *testing.T) {
 	}
 }
 
+func TestPreparePostVideo(t *testing.T) {
+	t.Parallel()
+
+	prepared, err := preparePostVideoHeader(t, "clip.mp4", tinyMP4())
+	if err != nil {
+		t.Fatal(err)
+	}
+	if prepared.extension != ".mp4" || prepared.contentType != "video/mp4" || len(prepared.body) == 0 {
+		t.Fatalf("prepared MP4 = %+v", prepared)
+	}
+	prepared, err = preparePostVideoHeader(t, "clip.webm", tinyWebM())
+	if err != nil {
+		t.Fatal(err)
+	}
+	if prepared.extension != ".webm" || prepared.contentType != "video/webm" {
+		t.Fatalf("prepared WebM = %+v", prepared)
+	}
+	if _, err := preparePostVideoHeader(t, "notes.txt", []byte("not a video")); err == nil {
+		t.Fatal("text video upload unexpectedly succeeded")
+	}
+	_, err = preparePostVideoHeader(t, "too-large.mp4", make([]byte, postVideoMaxFileBytes+1))
+	var requestErr *postImageRequestError
+	if !errors.As(err, &requestErr) || requestErr.status != http.StatusRequestEntityTooLarge {
+		t.Fatalf("oversized video error = %v, want 413 request error", err)
+	}
+}
+
 func TestOrientPostImage(t *testing.T) {
 	t.Parallel()
 
@@ -203,6 +231,76 @@ func TestPostImageMultipartLifecycle(t *testing.T) {
 	}
 }
 
+func TestPostVideoMultipartLifecycle(t *testing.T) {
+	t.Parallel()
+
+	blobs := &recordingImageBlob{}
+	srv, mem := newTestServer(t, Config{Blob: blobs})
+	handler := srv.Handler()
+	homeowner := seedUser(t, mem, uniq("video"), "hunter22", store.RoleUser)
+	cookies := loginUser(t, handler, homeowner.Username, "hunter22")
+	csrf := csrfForCookies(t, handler, cookies)
+
+	rec := multipartPost(t, handler, "/submit", map[string][]string{
+		"_csrf":             {csrf},
+		"title":             {"Valve clip"},
+		"body":              {"A photo and a video."},
+		"city":              {"Oakland"},
+		"image_description": {"Still", "Walkthrough"},
+	}, []multipartTestFile{
+		{name: "still.png", body: solidPNG(t, 40, 20)},
+		{name: "walk.mp4", body: tinyMP4()},
+	}, cookies)
+	if rec.Code != http.StatusSeeOther {
+		t.Fatalf("root video upload status = %d: %s", rec.Code, rec.Body.String())
+	}
+	roots, err := mem.ListRootPosts(context.Background(), pacific.Today(), homeowner.ID)
+	if err != nil || len(roots) != 1 {
+		t.Fatalf("roots = %+v, %v", roots, err)
+	}
+	root, err := mem.GetPost(context.Background(), roots[0].ID)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(root.Images) != 2 ||
+		root.Images[0].Kind != store.MediaKindImage ||
+		root.Images[1].Kind != store.MediaKindVideo ||
+		root.Images[1].Description != "Walkthrough" ||
+		!strings.HasPrefix(root.Images[1].ObjectKey, "post-videos/") {
+		t.Fatalf("root media = %+v", root.Images)
+	}
+
+	rec = multipartPost(t, handler, "/posts/"+root.ID+"/edit", map[string][]string{
+		"_csrf":                      {csrf},
+		"body":                       {"Keep the clip."},
+		"existing_image_id":          {root.Images[1].ID},
+		"existing_image_description": {"Kept clip"},
+	}, nil, cookies)
+	if rec.Code != http.StatusSeeOther {
+		t.Fatalf("retain video status = %d: %s", rec.Code, rec.Body.String())
+	}
+	edited, err := mem.GetPost(context.Background(), root.ID)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(edited.Images) != 1 || edited.Images[0].Kind != store.MediaKindVideo ||
+		edited.Images[0].Description != "Kept clip" {
+		t.Fatalf("retained video = %+v", edited.Images)
+	}
+
+	rec = multipartPost(t, handler, "/posts", map[string][]string{
+		"_csrf":     {csrf},
+		"parent_id": {root.ID},
+		"body":      {"Two clips."},
+	}, []multipartTestFile{
+		{name: "a.mp4", body: tinyMP4()},
+		{name: "b.mp4", body: tinyMP4()},
+	}, cookies)
+	if rec.Code != http.StatusBadRequest {
+		t.Fatalf("two-video status = %d, want 400", rec.Code)
+	}
+}
+
 func TestPostImageUploadCompensation(t *testing.T) {
 	t.Parallel()
 
@@ -318,6 +416,12 @@ func multipartPost(
 	return rec
 }
 
+func preparePostVideoHeader(t *testing.T, name string, body []byte) (preparedPostVideo, error) {
+	t.Helper()
+	header := multipartFileHeader(t, name, body)
+	return preparePostVideo(header)
+}
+
 func preparePostImageHeader(t *testing.T, name string, body []byte) (preparedPostImage, error) {
 	t.Helper()
 	var requestBody bytes.Buffer
@@ -341,6 +445,41 @@ func preparePostImageHeader(t *testing.T, name string, body []byte) (preparedPos
 	return preparePostImage(req.MultipartForm.File["images"][0])
 }
 
+func multipartFileHeader(t *testing.T, name string, body []byte) *multipart.FileHeader {
+	t.Helper()
+	var requestBody bytes.Buffer
+	writer := multipart.NewWriter(&requestBody)
+	part, err := writer.CreateFormFile("images", name)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if _, err := part.Write(body); err != nil {
+		t.Fatal(err)
+	}
+	if err := writer.Close(); err != nil {
+		t.Fatal(err)
+	}
+	req := httptest.NewRequest(http.MethodPost, "/posts", &requestBody)
+	req.Header.Set("Content-Type", writer.FormDataContentType())
+	if err := req.ParseMultipartForm(postImageMultipartMemory); err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(func() { _ = req.MultipartForm.RemoveAll() })
+	return req.MultipartForm.File["images"][0]
+}
+
+func tinyMP4() []byte {
+	body := make([]byte, 16)
+	body[3] = 16
+	copy(body[4:], "ftypisom")
+	copy(body[12:], "isom")
+	return body
+}
+
+func tinyWebM() []byte {
+	return []byte{0x1a, 0x45, 0xdf, 0xa3, 0x01, 0x00, 0x00, 0x00}
+}
+
 func solidPNG(t *testing.T, width, height int) []byte {
 	t.Helper()
 	img := image.NewNRGBA(image.Rect(0, 0, width, height))

internal/web/posts.go

@@ -5,16 +5,13 @@ import (
 	"database/sql"
 	"errors"
 	"fmt"
-	"log"
 	"net/http"
 	"net/url"
 	"strings"
-	"time"
 
 	"github.com/go-chi/chi/v5"
 	"github.com/google/uuid"
 
-	"plumber/internal/mail"
 	"plumber/internal/store"
 )
 
@@ -96,9 +93,7 @@ func (s *Server) handleCreatePost(w http.ResponseWriter, r *http.Request) {
 	if root == nil {
 		root = post
 	}
-	if parent != nil {
-		s.notifyPostReply(parent, root, post, user)
-	}
+	s.publishPostCreated(post, root, user)
 	http.Redirect(
 		w,
 		r,
@@ -107,59 +102,6 @@ func (s *Server) handleCreatePost(w http.ResponseWriter, r *http.Request) {
 	)
 }
 
-// notifyPostReply emails the root homeowner for admin replies and the direct
-// parent author for homeowner replies.
-func (s *Server) notifyPostReply(
-	parent *store.Post,
-	root *store.Post,
-	reply *store.Post,
-	replyAuthor *store.User,
-) {
-	if parent == nil ||
-		root == nil ||
-		reply == nil ||
-		replyAuthor == nil ||
-		s.cfg.Mail == nil {
-		return
-	}
-	if _, disabled := s.cfg.Mail.(mail.Nop); disabled {
-		return
-	}
-	recipientID := parent.AuthorID
-	if replyAuthor.Admin() {
-		recipientID = root.AuthorID
-	}
-	if recipientID == replyAuthor.ID {
-		return
-	}
-	msg := mail.PostReply{
-		RootID:          root.ID,
-		RootTitle:       root.Title,
-		ReplyID:         reply.ID,
-		ReplyBody:       reply.Body,
-		ReplyAuthorName: replyAuthor.Name,
-	}
-	go func() {
-		ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
-		defer cancel()
-		recipient, err := s.store.UserByID(ctx, recipientID)
-		if err != nil {
-			log.Printf("notify reply %s: load recipient: %v", msg.ReplyID, err)
-			return
-		}
-		if recipient == nil || strings.TrimSpace(recipient.Email) == "" {
-			return
-		}
-		msg.ToEmail = recipient.Email
-		msg.ToName = recipient.Name
-		if err := s.cfg.Mail.NotifyPostReply(ctx, msg); err != nil {
-			log.Printf("notify reply %s: %v", msg.ReplyID, err)
-			return
-		}
-		log.Printf("notify reply %s: accepted", msg.ReplyID)
-	}()
-}
-
 // handleEditPost updates only a post's body after verifying that the current
 // homeowner owns it or that an admin is editing an admin-authored post.
 func (s *Server) handleEditPost(w http.ResponseWriter, r *http.Request) {
@@ -218,6 +160,7 @@ func (s *Server) handleEditPost(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 	s.deletePostImageObjects(removedPostImageKeys(previousImages, images))
+	s.publishPostUpdated(post, root, nil)
 	http.Redirect(
 		w,
 		r,

internal/web/posts_test.go

@@ -9,6 +9,7 @@ import (
 	"testing"
 	"time"
 
+	"plumber/internal/events"
 	"plumber/internal/mail"
 	"plumber/internal/pacific"
 	"plumber/internal/store"
@@ -263,8 +264,12 @@ func TestEditPostRoutePermissions(t *testing.T) {
 func TestPostReplyNotifications(t *testing.T) {
 	t.Parallel()
 
+	mem := store.NewMemory()
+	bus := events.New()
+	defer bus.Close()
 	recording := &mail.Recording{}
-	srv, mem := newTestServer(t, Config{Mail: recording})
+	mail.Subscribe(bus, mem, recording)
+	srv := newTestServerStore(t, mem, Config{Events: bus})
 	handler := srv.Handler()
 	homeowner := seedUser(t, mem, uniq("homeowner"), "hunter22", store.RoleUser)
 	admin := seedUser(t, mem, uniq("admin"), "hunter22", store.RoleAdmin)

internal/web/server.go

@@ -21,8 +21,8 @@ import (
 	"github.com/google/uuid"
 
 	"plumber/internal/blob"
+	"plumber/internal/events"
 	"plumber/internal/geo"
-	"plumber/internal/mail"
 	"plumber/internal/pacific"
 	"plumber/internal/store"
 )
@@ -35,7 +35,8 @@ type Config struct {
 	// TrustedProxies are CIDRs allowed to set X-Forwarded-For (direct peer).
 	TrustedProxies []*net.IPNet
 	Blob           blob.Uploader
-	Mail           mail.Notifier
+	Events         events.Publisher
+	BaseURL        string
 }
 
 type Server struct {
@@ -113,8 +114,8 @@ func New(st store.Store, sessionStore scs.Store, templateFS fs.FS, staticFS fs.F
 	if cfg.Blob == nil {
 		cfg.Blob = blob.Disabled{}
 	}
-	if cfg.Mail == nil {
-		cfg.Mail = mail.Nop{}
+	if cfg.Events == nil {
+		cfg.Events = events.Nop{}
 	}
 	funcMap := template.FuncMap{
 		"voteCtx": func(user *store.User, csrf, view, date string, post *store.Post) voteCtx {
@@ -396,6 +397,7 @@ func (s *Server) handleSubmit(w http.ResponseWriter, r *http.Request) {
 		http.Error(w, "could not save question", http.StatusInternalServerError)
 		return
 	}
+	s.publishPostCreated(post, post, u)
 	http.Redirect(w, r, "/questions/"+url.PathEscape(post.ID), http.StatusSeeOther)
 }
 

schema.sql

@@ -48,13 +48,23 @@ CREATE TABLE IF NOT EXISTS post_images (
   object_key TEXT NOT NULL UNIQUE,
   public_url TEXT NOT NULL,
   description TEXT NOT NULL DEFAULT '' CHECK (char_length(description) <= 500),
-  position SMALLINT NOT NULL CHECK (position BETWEEN 0 AND 3),
-  width INTEGER NOT NULL CHECK (width > 0),
-  height INTEGER NOT NULL CHECK (height > 0),
+  kind TEXT NOT NULL DEFAULT 'image',
+  position SMALLINT NOT NULL,
+  width INTEGER NOT NULL,
+  height INTEGER NOT NULL,
   created_at TEXT NOT NULL,
+  CONSTRAINT post_images_kind_check CHECK (kind IN ('image', 'video')),
+  CONSTRAINT post_images_width_check CHECK (width >= 0),
+  CONSTRAINT post_images_height_check CHECK (height >= 0),
+  CONSTRAINT post_images_image_dims_check CHECK (kind <> 'image' OR (width > 0 AND height > 0)),
+  CONSTRAINT post_images_position_check CHECK (position BETWEEN 0 AND 4),
   UNIQUE (post_id, position)
 );
 
+CREATE UNIQUE INDEX IF NOT EXISTS post_images_one_video_uidx
+  ON post_images (post_id)
+  WHERE kind = 'video';
+
 CREATE TABLE IF NOT EXISTS post_votes (
   user_id TEXT NOT NULL REFERENCES users(id),
   post_id TEXT NOT NULL REFERENCES posts(id) ON DELETE CASCADE,
@@ -65,6 +75,17 @@ CREATE TABLE IF NOT EXISTS post_votes (
 CREATE INDEX IF NOT EXISTS idx_post_votes_post_id
   ON post_votes(post_id);
 
+CREATE TABLE IF NOT EXISTS discord_post_links (
+  post_id TEXT PRIMARY KEY REFERENCES posts(id) ON DELETE CASCADE,
+  discord_message_id TEXT NOT NULL UNIQUE,
+  discord_thread_id TEXT NOT NULL DEFAULT '',
+  created_at TEXT NOT NULL
+);
+
+CREATE UNIQUE INDEX IF NOT EXISTS discord_post_links_thread_uidx
+  ON discord_post_links (discord_thread_id)
+  WHERE discord_thread_id <> '';
+
 CREATE TABLE IF NOT EXISTS sessions (
   token TEXT PRIMARY KEY,
   data BYTEA NOT NULL,