Add unified post storage.

Provide one creation path for roots and replies, recursive thread loading, body-only updates, root listings, and post voting across PostgreSQL and the in-memory test store.

db/queries/posts.sql

@@ -0,0 +1,112 @@
+-- name: CreatePost :exec
+INSERT INTO posts (
+  id, parent_id, author_id, title, body, city, post_date, hidden, created_at, updated_at
+)
+VALUES ($1, $2, $3, $4, $5, $6, $7, $8, $9, $10);
+
+-- name: GetPost :one
+SELECT
+  p.id, p.parent_id, p.author_id, u.name AS author_name, u.role AS author_role,
+  p.title, p.body, p.city, p.post_date, p.hidden, p.created_at, p.updated_at
+FROM posts p
+JOIN users u ON u.id = p.author_id
+WHERE p.id = $1;
+
+-- name: ListPostThread :many
+WITH RECURSIVE thread AS (
+  SELECT p.*
+  FROM posts p
+  WHERE p.id = $1 AND p.parent_id IS NULL
+
+  UNION ALL
+
+  SELECT child.*
+  FROM posts child
+  JOIN thread parent ON child.parent_id = parent.id
+)
+SELECT
+  thread.id, thread.parent_id, thread.author_id,
+  u.name AS author_name, u.role AS author_role,
+  thread.title, thread.body, thread.city, thread.post_date,
+  thread.hidden, thread.created_at, thread.updated_at
+FROM thread
+JOIN users u ON u.id = thread.author_id
+ORDER BY thread.created_at, thread.id;
+
+-- name: UpdatePost :execrows
+UPDATE posts
+SET body = $2, updated_at = $3
+WHERE id = $1;
+
+-- name: ListRootPosts :many
+WITH RECURSIVE roots AS (
+  SELECT p.*
+  FROM posts p
+  WHERE p.parent_id IS NULL
+    AND p.post_date = sqlc.arg(post_date)
+    AND p.hidden = 0
+),
+thread AS (
+  SELECT roots.id AS root_id, roots.id AS post_id, roots.author_id
+  FROM roots
+
+  UNION ALL
+
+  SELECT thread.root_id, child.id, child.author_id
+  FROM thread
+  JOIN posts child ON child.parent_id = thread.post_id
+),
+answered AS (
+  SELECT thread.root_id, bool_or(u.role = 'admin' AND thread.post_id <> thread.root_id) AS answered
+  FROM thread
+  JOIN users u ON u.id = thread.author_id
+  GROUP BY thread.root_id
+),
+scores AS (
+  SELECT post_id, COALESCE(SUM(value), 0)::bigint AS score
+  FROM post_votes
+  GROUP BY post_id
+)
+SELECT
+  roots.id, roots.parent_id, roots.author_id,
+  u.name AS author_name, u.role AS author_role,
+  roots.title, roots.body, roots.city, roots.post_date,
+  roots.hidden, roots.created_at, roots.updated_at,
+  COALESCE(scores.score, 0)::bigint AS score,
+  COALESCE(answered.answered, false)::bool AS answered,
+  COALESCE((
+    SELECT post_votes.value
+    FROM post_votes
+    WHERE post_votes.user_id = sqlc.arg(viewer_id)
+      AND post_votes.post_id = roots.id
+  ), 0)::bigint AS user_vote
+FROM roots
+JOIN users u ON u.id = roots.author_id
+LEFT JOIN scores ON scores.post_id = roots.id
+LEFT JOIN answered ON answered.root_id = roots.id
+ORDER BY score DESC, roots.created_at, roots.id
+LIMIT sqlc.arg(row_limit);
+
+-- name: PostIsVisibleRoot :one
+SELECT EXISTS(
+  SELECT 1
+  FROM posts
+  WHERE id = $1 AND parent_id IS NULL AND hidden = 0
+)::bool;
+
+-- name: DeletePostVote :exec
+DELETE FROM post_votes
+WHERE user_id = $1 AND post_id = $2;
+
+-- name: UpsertPostVoteOnVisibleRoot :execrows
+INSERT INTO post_votes (user_id, post_id, value)
+SELECT $1, $2, $3
+FROM posts p
+WHERE p.id = $2 AND p.parent_id IS NULL AND p.hidden = 0
+ON CONFLICT (user_id, post_id) DO UPDATE
+SET value = excluded.value
+WHERE EXISTS (
+  SELECT 1
+  FROM posts p2
+  WHERE p2.id = excluded.post_id AND p2.parent_id IS NULL AND p2.hidden = 0
+);

internal/store/memory.go

@@ -22,6 +22,8 @@ type Memory struct {
 	questions map[string]*RankedQuestion // id -> question
 	answers   map[string]*Answer         // questionID -> answer
 	votes     map[string]map[string]int  // questionID -> userID -> value
+	posts     map[string]*Post           // id -> post
+	postVotes map[string]map[string]int  // postID -> userID -> value
 }
 
 // NewMemory returns an empty Memory store.
@@ -32,6 +34,8 @@ func NewMemory() *Memory {
 		questions: map[string]*RankedQuestion{},
 		answers:   map[string]*Answer{},
 		votes:     map[string]map[string]int{},
+		posts:     map[string]*Post{},
+		postVotes: map[string]map[string]int{},
 	}
 }
 
@@ -372,6 +376,186 @@ func (m *Memory) UpsertAnswer(_ context.Context, a *Answer) error {
 	return nil
 }
 
+func (m *Memory) CreatePost(_ context.Context, post *Post) error {
+	if post == nil {
+		return fmt.Errorf("%w: post is nil", ErrInvalidPost)
+	}
+	if err := preparePost(post); err != nil {
+		return err
+	}
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	if _, ok := m.users[post.AuthorID]; !ok {
+		return fmt.Errorf("%w: unknown author", ErrInvalidPost)
+	}
+	if _, exists := m.posts[post.ID]; exists {
+		return fmt.Errorf("%w: duplicate id", ErrInvalidPost)
+	}
+	if post.ParentID != nil {
+		if _, ok := m.posts[*post.ParentID]; !ok {
+			return fmt.Errorf("%w: unknown parent", ErrInvalidPost)
+		}
+	}
+	cp := clonePost(post)
+	cp.db = nil
+	m.posts[cp.ID] = cp
+	*post = *clonePost(cp)
+	return nil
+}
+
+func (m *Memory) GetPost(_ context.Context, id string) (*Post, error) {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	post, ok := m.posts[id]
+	if !ok {
+		return nil, sql.ErrNoRows
+	}
+	return clonePostWithAuthor(post, m.users), nil
+}
+
+func (m *Memory) GetPostThread(_ context.Context, rootID string) (*Post, error) {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	root, ok := m.posts[rootID]
+	if !ok || root.ParentID != nil {
+		return nil, sql.ErrNoRows
+	}
+	inThread := map[string]bool{rootID: true}
+	for changed := true; changed; {
+		changed = false
+		for id, post := range m.posts {
+			if inThread[id] || post.ParentID == nil || !inThread[*post.ParentID] {
+				continue
+			}
+			inThread[id] = true
+			changed = true
+		}
+	}
+	posts := make([]Post, 0, len(inThread))
+	for id := range inThread {
+		posts = append(posts, *clonePostWithAuthor(m.posts[id], m.users))
+	}
+	return buildPostTree(posts, rootID)
+}
+
+func (m *Memory) UpdatePost(_ context.Context, post *Post) error {
+	if post == nil {
+		return fmt.Errorf("%w: post is nil", ErrInvalidPost)
+	}
+	body := strings.TrimSpace(post.Body)
+	if body == "" {
+		return fmt.Errorf("%w: body is required", ErrInvalidPost)
+	}
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	existing, ok := m.posts[post.ID]
+	if !ok {
+		return sql.ErrNoRows
+	}
+	existing.Body = body
+	existing.UpdatedAt = time.Now().UTC().Format(time.RFC3339Nano)
+	*post = *clonePostWithAuthor(existing, m.users)
+	return nil
+}
+
+func (m *Memory) ListRootPosts(_ context.Context, postDate, viewerID string) ([]Post, error) {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	posts := make([]Post, 0)
+	for _, post := range m.posts {
+		if post.ParentID != nil || post.PostDate != postDate || post.Hidden {
+			continue
+		}
+		cp := clonePostWithAuthor(post, m.users)
+		for _, value := range m.postVotes[post.ID] {
+			cp.Score += value
+		}
+		cp.UserVote = m.postVotes[post.ID][viewerID]
+		cp.Answered = m.threadContainsAdminReply(post.ID)
+		posts = append(posts, *cp)
+	}
+	sort.Slice(posts, func(i, j int) bool {
+		if posts[i].Score != posts[j].Score {
+			return posts[i].Score > posts[j].Score
+		}
+		if posts[i].CreatedAt != posts[j].CreatedAt {
+			return posts[i].CreatedAt < posts[j].CreatedAt
+		}
+		return posts[i].ID < posts[j].ID
+	})
+	if len(posts) > HuntListLimit {
+		posts = posts[:HuntListLimit]
+	}
+	return posts, nil
+}
+
+func (m *Memory) VotePost(_ context.Context, userID, postID string, value int) error {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	if value != 1 && value != -1 && value != 0 {
+		return fmt.Errorf("invalid vote")
+	}
+	post, ok := m.posts[postID]
+	if !ok || post.ParentID != nil || post.Hidden {
+		return ErrPostNotVotable
+	}
+	if m.postVotes[postID] == nil {
+		m.postVotes[postID] = map[string]int{}
+	}
+	if value == 0 {
+		delete(m.postVotes[postID], userID)
+		return nil
+	}
+	m.postVotes[postID][userID] = value
+	return nil
+}
+
+func (m *Memory) threadContainsAdminReply(rootID string) bool {
+	for id, post := range m.posts {
+		if id == rootID || !m.postIsDescendantOf(post, rootID) {
+			continue
+		}
+		if author := m.users[post.AuthorID]; author != nil && author.Role == RoleAdmin {
+			return true
+		}
+	}
+	return false
+}
+
+func (m *Memory) postIsDescendantOf(post *Post, rootID string) bool {
+	seen := map[string]bool{}
+	for post != nil && post.ParentID != nil {
+		if *post.ParentID == rootID {
+			return true
+		}
+		if seen[*post.ParentID] {
+			return false
+		}
+		seen[*post.ParentID] = true
+		post = m.posts[*post.ParentID]
+	}
+	return false
+}
+
+func clonePost(post *Post) *Post {
+	cp := *post
+	if post.ParentID != nil {
+		parentID := *post.ParentID
+		cp.ParentID = &parentID
+	}
+	cp.Replies = nil
+	return &cp
+}
+
+func clonePostWithAuthor(post *Post, users map[string]*User) *Post {
+	cp := clonePost(post)
+	if author := users[post.AuthorID]; author != nil {
+		cp.AuthorName = author.Name
+		cp.AuthorRole = author.Role
+	}
+	return cp
+}
+
 func (m *Memory) Vote(_ context.Context, userID, questionID string, value int) error {
 	m.mu.Lock()
 	defer m.mu.Unlock()

internal/store/migrate_posts_test.go

@@ -9,6 +9,8 @@ import (
 	"testing"
 
 	"github.com/google/uuid"
+
+	"plumber/internal/store/sqlc"
 )
 
 func TestMigratePostsCopiesLegacyData(t *testing.T) {
@@ -47,7 +49,9 @@ func TestMigratePostsCopiesLegacyData(t *testing.T) {
 
 	legacySchema := `
 CREATE TABLE users (
-  id TEXT PRIMARY KEY
+  id TEXT PRIMARY KEY,
+  name TEXT NOT NULL,
+  role TEXT NOT NULL
 );
 CREATE TABLE questions (
   id TEXT PRIMARY KEY,
@@ -76,7 +80,8 @@ CREATE TABLE votes (
 		t.Fatal(err)
 	}
 	if _, err := conn.ExecContext(ctx, `
-INSERT INTO users (id) VALUES ('homeowner'), ('plumber');
+INSERT INTO users (id, name, role)
+VALUES ('homeowner', 'Home Owner', 'user'), ('plumber', 'The Plumber', 'admin');
 INSERT INTO questions (id, author_id, title, body, city, hunt_date, hidden, created_at)
 VALUES ('question-1', 'homeowner', 'Leaky sink', 'It drips.', 'Oakland', '2026-08-26', 0, '2026-08-26T08:00:00Z');
 INSERT INTO answers (question_id, author_id, body, created_at, updated_at)
@@ -183,6 +188,56 @@ INSERT INTO posts (
 )`); err == nil {
 		t.Fatal("reply with root-only title unexpectedly succeeded")
 	}
+
+	queries := sqlc.New(conn)
+	if err := queries.CreatePost(ctx, sqlc.CreatePostParams{
+		ID:        "follow-up",
+		ParentID:  sql.NullString{String: "answer:question-1", Valid: true},
+		AuthorID:  "homeowner",
+		Body:      "It is still dripping.",
+		CreatedAt: "2026-08-26T10:00:00Z",
+		UpdatedAt: "2026-08-26T10:00:00Z",
+	}); err != nil {
+		t.Fatal(err)
+	}
+	thread, err := queries.ListPostThread(ctx, "question-1")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(thread) != 3 ||
+		thread[0].ID != "question-1" ||
+		thread[1].ID != "answer:question-1" ||
+		thread[2].ID != "follow-up" {
+		t.Fatalf("recursive thread = %+v", thread)
+	}
+	if n, err := queries.UpdatePost(ctx, sqlc.UpdatePostParams{
+		ID:        "follow-up",
+		Body:      "The drip continues.",
+		UpdatedAt: "2026-08-26T10:05:00Z",
+	}); err != nil || n != 1 {
+		t.Fatalf("update rows=%d error=%v", n, err)
+	}
+	if n, err := queries.UpsertPostVoteOnVisibleRoot(ctx, sqlc.UpsertPostVoteOnVisibleRootParams{
+		UserID: "plumber",
+		PostID: "question-1",
+		Value:  1,
+	}); err != nil || n != 1 {
+		t.Fatalf("vote rows=%d error=%v", n, err)
+	}
+	roots, err := queries.ListRootPosts(ctx, sqlc.ListRootPostsParams{
+		ViewerID: "plumber",
+		RowLimit: 100,
+		PostDate: "2026-08-26",
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(roots) != 1 ||
+		roots[0].Score != 2 ||
+		!roots[0].Answered ||
+		roots[0].UserVote != 1 {
+		t.Fatalf("root annotations = %+v", roots)
+	}
 }
 
 func TestMigratePostsReportsStep(t *testing.T) {

internal/store/post.go

@@ -0,0 +1,358 @@
+package store
+
+import (
+	"context"
+	"database/sql"
+	"errors"
+	"fmt"
+	"sort"
+	"strings"
+	"time"
+
+	"github.com/google/uuid"
+	"github.com/jackc/pgx/v5/pgconn"
+
+	"plumber/internal/pacific"
+	"plumber/internal/store/sqlc"
+)
+
+var (
+	ErrInvalidPost    = errors.New("invalid post")
+	ErrPostNotVotable = errors.New("post not votable")
+)
+
+// Post is either a root question (ParentID nil) or a reply to another post.
+type Post struct {
+	ID         string
+	ParentID   *string
+	AuthorID   string
+	AuthorName string
+	AuthorRole Role
+	Title      string
+	Body       string
+	City       string
+	PostDate   string
+	Hidden     bool
+	CreatedAt  string
+	UpdatedAt  string
+	Score      int
+	Answered   bool
+	UserVote   int
+	Replies    []*Post
+	db         *sql.DB
+}
+
+// NewPost returns a post bound to db.
+func NewPost(db *sql.DB) *Post {
+	return &Post{db: db}
+}
+
+// Create inserts a root post or reply according to ParentID.
+func (p *Post) Create(ctx context.Context) error {
+	if p == nil || p.db == nil {
+		return fmt.Errorf("post: no database")
+	}
+	if err := preparePost(p); err != nil {
+		return err
+	}
+	err := sqlc.New(p.db).CreatePost(ctx, sqlc.CreatePostParams{
+		ID:        p.ID,
+		ParentID:  nullableParentID(p.ParentID),
+		AuthorID:  p.AuthorID,
+		Title:     p.Title,
+		Body:      p.Body,
+		City:      p.City,
+		PostDate:  p.PostDate,
+		Hidden:    boolInt32(p.Hidden),
+		CreatedAt: p.CreatedAt,
+		UpdatedAt: p.UpdatedAt,
+	})
+	return mapPostCreateError(err)
+}
+
+// Update changes only the post body and update timestamp.
+func (p *Post) Update(ctx context.Context) error {
+	if p == nil || p.db == nil {
+		return fmt.Errorf("post: no database")
+	}
+	p.Body = strings.TrimSpace(p.Body)
+	if p.Body == "" {
+		return fmt.Errorf("%w: body is required", ErrInvalidPost)
+	}
+	p.UpdatedAt = time.Now().UTC().Format(time.RFC3339Nano)
+	n, err := sqlc.New(p.db).UpdatePost(ctx, sqlc.UpdatePostParams{
+		ID:        p.ID,
+		Body:      p.Body,
+		UpdatedAt: p.UpdatedAt,
+	})
+	if err != nil {
+		return err
+	}
+	if n == 0 {
+		return sql.ErrNoRows
+	}
+	return nil
+}
+
+func preparePost(p *Post) error {
+	p.ID = strings.TrimSpace(p.ID)
+	p.AuthorID = strings.TrimSpace(p.AuthorID)
+	p.Title = strings.TrimSpace(p.Title)
+	p.Body = strings.TrimSpace(p.Body)
+	p.City = strings.TrimSpace(p.City)
+	p.PostDate = strings.TrimSpace(p.PostDate)
+	if p.AuthorID == "" {
+		return fmt.Errorf("%w: author is required", ErrInvalidPost)
+	}
+	if p.Body == "" {
+		return fmt.Errorf("%w: body is required", ErrInvalidPost)
+	}
+	if p.ParentID == nil {
+		if p.Title == "" {
+			return fmt.Errorf("%w: root title is required", ErrInvalidPost)
+		}
+		if p.PostDate == "" {
+			p.PostDate = pacific.Today()
+		}
+	} else {
+		parentID := strings.TrimSpace(*p.ParentID)
+		if parentID == "" {
+			return fmt.Errorf("%w: parent is required", ErrInvalidPost)
+		}
+		p.ParentID = &parentID
+		if p.Title != "" || p.City != "" || p.PostDate != "" || p.Hidden {
+			return fmt.Errorf("%w: reply contains root-only fields", ErrInvalidPost)
+		}
+	}
+	if p.ID == "" {
+		p.ID = uuid.NewString()
+	}
+	now := time.Now().UTC().Format(time.RFC3339Nano)
+	if p.CreatedAt == "" {
+		p.CreatedAt = now
+	}
+	if p.UpdatedAt == "" {
+		p.UpdatedAt = p.CreatedAt
+	}
+	return nil
+}
+
+func nullableParentID(parentID *string) sql.NullString {
+	if parentID == nil {
+		return sql.NullString{}
+	}
+	return sql.NullString{String: *parentID, Valid: true}
+}
+
+func parentIDFromNull(parentID sql.NullString) *string {
+	if !parentID.Valid {
+		return nil
+	}
+	id := parentID.String
+	return &id
+}
+
+func boolInt32(value bool) int32 {
+	if value {
+		return 1
+	}
+	return 0
+}
+
+func mapPostCreateError(err error) error {
+	if err == nil {
+		return nil
+	}
+	var pgErr *pgconn.PgError
+	if errors.As(err, &pgErr) {
+		switch pgErr.Code {
+		case "23503", "23505", "23514":
+			return fmt.Errorf("%w: %v", ErrInvalidPost, err)
+		}
+	}
+	return err
+}
+
+func postFromValues(
+	db *sql.DB,
+	id string,
+	parentID sql.NullString,
+	authorID, authorName, authorRole, title, body, city, postDate string,
+	hidden int32,
+	createdAt, updatedAt string,
+) Post {
+	return Post{
+		ID:         id,
+		ParentID:   parentIDFromNull(parentID),
+		AuthorID:   authorID,
+		AuthorName: authorName,
+		AuthorRole: Role(authorRole),
+		Title:      title,
+		Body:       body,
+		City:       city,
+		PostDate:   postDate,
+		Hidden:     hidden != 0,
+		CreatedAt:  createdAt,
+		UpdatedAt:  updatedAt,
+		db:         db,
+	}
+}
+
+// GetPost returns one post without loading its replies.
+func GetPost(ctx context.Context, db *sql.DB, id string) (*Post, error) {
+	r, err := sqlc.New(db).GetPost(ctx, id)
+	if err != nil {
+		return nil, err
+	}
+	p := postFromValues(
+		db,
+		r.ID,
+		r.ParentID,
+		r.AuthorID,
+		r.AuthorName,
+		r.AuthorRole,
+		r.Title,
+		r.Body,
+		r.City,
+		r.PostDate,
+		r.Hidden,
+		r.CreatedAt,
+		r.UpdatedAt,
+	)
+	return &p, nil
+}
+
+// GetPostThread returns a root post with all descendants nested under Replies.
+func GetPostThread(ctx context.Context, db *sql.DB, rootID string) (*Post, error) {
+	rows, err := sqlc.New(db).ListPostThread(ctx, rootID)
+	if err != nil {
+		return nil, err
+	}
+	posts := make([]Post, 0, len(rows))
+	for _, r := range rows {
+		posts = append(posts, postFromValues(
+			db,
+			r.ID,
+			r.ParentID,
+			r.AuthorID,
+			r.AuthorName,
+			r.AuthorRole,
+			r.Title,
+			r.Body,
+			r.City,
+			r.PostDate,
+			r.Hidden,
+			r.CreatedAt,
+			r.UpdatedAt,
+		))
+	}
+	return buildPostTree(posts, rootID)
+}
+
+func buildPostTree(posts []Post, rootID string) (*Post, error) {
+	byID := make(map[string]*Post, len(posts))
+	for i := range posts {
+		posts[i].Replies = nil
+		byID[posts[i].ID] = &posts[i]
+	}
+	root, ok := byID[rootID]
+	if !ok || root.ParentID != nil {
+		return nil, sql.ErrNoRows
+	}
+	for i := range posts {
+		post := &posts[i]
+		if post.ID == rootID {
+			continue
+		}
+		if post.ParentID == nil {
+			return nil, fmt.Errorf("post %s is not in thread %s", post.ID, rootID)
+		}
+		parent, ok := byID[*post.ParentID]
+		if !ok {
+			return nil, fmt.Errorf("post %s has missing parent %s", post.ID, *post.ParentID)
+		}
+		parent.Replies = append(parent.Replies, post)
+	}
+	var sortReplies func(*Post)
+	sortReplies = func(post *Post) {
+		sort.Slice(post.Replies, func(i, j int) bool {
+			if post.Replies[i].CreatedAt != post.Replies[j].CreatedAt {
+				return post.Replies[i].CreatedAt < post.Replies[j].CreatedAt
+			}
+			return post.Replies[i].ID < post.Replies[j].ID
+		})
+		for _, reply := range post.Replies {
+			sortReplies(reply)
+		}
+	}
+	sortReplies(root)
+	return root, nil
+}
+
+// ListRootPosts returns visible root posts for a post date.
+func ListRootPosts(ctx context.Context, db *sql.DB, postDate, viewerID string) ([]Post, error) {
+	rows, err := sqlc.New(db).ListRootPosts(ctx, sqlc.ListRootPostsParams{
+		ViewerID: viewerID,
+		RowLimit: HuntListLimit,
+		PostDate: postDate,
+	})
+	if err != nil {
+		return nil, err
+	}
+	posts := make([]Post, 0, len(rows))
+	for _, r := range rows {
+		post := postFromValues(
+			db,
+			r.ID,
+			r.ParentID,
+			r.AuthorID,
+			r.AuthorName,
+			r.AuthorRole,
+			r.Title,
+			r.Body,
+			r.City,
+			r.PostDate,
+			r.Hidden,
+			r.CreatedAt,
+			r.UpdatedAt,
+		)
+		post.Score = int(r.Score)
+		post.Answered = r.Answered
+		post.UserVote = int(r.UserVote)
+		posts = append(posts, post)
+	}
+	return posts, nil
+}
+
+// SetPostVote sets value to 1, -1, or 0 on a visible root post.
+func SetPostVote(ctx context.Context, db *sql.DB, userID, postID string, value int) error {
+	if value != 1 && value != -1 && value != 0 {
+		return fmt.Errorf("invalid vote")
+	}
+	q := sqlc.New(db)
+	if value == 0 {
+		visible, err := q.PostIsVisibleRoot(ctx, postID)
+		if err != nil {
+			return err
+		}
+		if !visible {
+			return ErrPostNotVotable
+		}
+		return q.DeletePostVote(ctx, sqlc.DeletePostVoteParams{
+			UserID: userID,
+			PostID: postID,
+		})
+	}
+	n, err := q.UpsertPostVoteOnVisibleRoot(ctx, sqlc.UpsertPostVoteOnVisibleRootParams{
+		UserID: userID,
+		PostID: postID,
+		Value:  int32(value),
+	})
+	if err != nil {
+		return err
+	}
+	if n == 0 {
+		return ErrPostNotVotable
+	}
+	return nil
+}

internal/store/post_test.go

@@ -0,0 +1,209 @@
+package store
+
+import (
+	"context"
+	"database/sql"
+	"errors"
+	"testing"
+
+	"github.com/jackc/pgx/v5/pgconn"
+)
+
+func TestMapPostCreateError(t *testing.T) {
+	t.Parallel()
+
+	for _, code := range []string{"23503", "23505", "23514"} {
+		err := mapPostCreateError(&pgconn.PgError{Code: code})
+		if !errors.Is(err, ErrInvalidPost) {
+			t.Errorf("code %s error = %v, want ErrInvalidPost", code, err)
+		}
+	}
+	original := &pgconn.PgError{Code: "08006"}
+	if err := mapPostCreateError(original); !errors.Is(err, original) {
+		t.Errorf("unexpected database error was replaced: %v", err)
+	}
+}
+
+func TestMemoryPostLifecycle(t *testing.T) {
+	t.Parallel()
+
+	ctx := context.Background()
+	mem := NewMemory()
+	homeowner := &User{Username: "homeowner", PasswordHash: "hash", Role: RoleUser}
+	plumber := &User{Username: "plumber", PasswordHash: "hash", Role: RoleAdmin}
+	voter := &User{Username: "voter", PasswordHash: "hash", Role: RoleUser}
+	for _, user := range []*User{homeowner, plumber, voter} {
+		if err := mem.CreateUser(ctx, user); err != nil {
+			t.Fatal(err)
+		}
+	}
+
+	root := &Post{
+		ID:        "root",
+		AuthorID:  homeowner.ID,
+		Title:     "Leaky sink",
+		Body:      "It drips.",
+		City:      "Oakland",
+		PostDate:  "2026-08-26",
+		CreatedAt: "2026-08-26T08:00:00Z",
+	}
+	if err := mem.CreatePost(ctx, root); err != nil {
+		t.Fatal(err)
+	}
+
+	rootID := root.ID
+	later := &Post{
+		ID:        "later",
+		ParentID:  &rootID,
+		AuthorID:  plumber.ID,
+		Body:      "Is it a single-handle faucet?",
+		CreatedAt: "2026-08-26T09:00:00Z",
+	}
+	earlier := &Post{
+		ID:        "earlier",
+		ParentID:  &rootID,
+		AuthorID:  plumber.ID,
+		Body:      "Can you share the model number?",
+		CreatedAt: "2026-08-26T08:30:00Z",
+	}
+	if err := mem.CreatePost(ctx, later); err != nil {
+		t.Fatal(err)
+	}
+	if err := mem.CreatePost(ctx, earlier); err != nil {
+		t.Fatal(err)
+	}
+
+	laterID := later.ID
+	nested := &Post{
+		ID:        "nested",
+		ParentID:  &laterID,
+		AuthorID:  homeowner.ID,
+		Body:      "Yes, it is.",
+		CreatedAt: "2026-08-26T09:30:00Z",
+	}
+	if err := mem.CreatePost(ctx, nested); err != nil {
+		t.Fatal(err)
+	}
+
+	thread, err := mem.GetPostThread(ctx, root.ID)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if thread.AuthorName != homeowner.Name || thread.AuthorRole != RoleUser {
+		t.Fatalf("root author = %q %q", thread.AuthorName, thread.AuthorRole)
+	}
+	if len(thread.Replies) != 2 ||
+		thread.Replies[0].ID != earlier.ID ||
+		thread.Replies[1].ID != later.ID {
+		t.Fatalf("root replies are not oldest-first: %+v", thread.Replies)
+	}
+	if len(thread.Replies[1].Replies) != 1 || thread.Replies[1].Replies[0].ID != nested.ID {
+		t.Fatalf("nested reply missing: %+v", thread.Replies[1].Replies)
+	}
+
+	otherParent := earlier.ID
+	nested.ParentID = &otherParent
+	nested.AuthorID = voter.ID
+	nested.Body = "Yes—one handle."
+	if err := mem.UpdatePost(ctx, nested); err != nil {
+		t.Fatal(err)
+	}
+	saved, err := mem.GetPost(ctx, nested.ID)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if saved.ParentID == nil || *saved.ParentID != later.ID {
+		t.Fatalf("update changed parent to %+v", saved.ParentID)
+	}
+	if saved.AuthorID != homeowner.ID {
+		t.Fatalf("update changed author to %q", saved.AuthorID)
+	}
+	if saved.Body != "Yes—one handle." || saved.UpdatedAt == saved.CreatedAt {
+		t.Fatalf("body update not applied: %+v", saved)
+	}
+
+	if err := mem.VotePost(ctx, voter.ID, root.ID, 1); err != nil {
+		t.Fatal(err)
+	}
+	roots, err := mem.ListRootPosts(ctx, root.PostDate, voter.ID)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(roots) != 1 || roots[0].ID != root.ID {
+		t.Fatalf("root list = %+v", roots)
+	}
+	if roots[0].Score != 1 || roots[0].UserVote != 1 || !roots[0].Answered {
+		t.Fatalf("root annotations = %+v", roots[0])
+	}
+	if err := mem.VotePost(ctx, voter.ID, later.ID, 1); !errors.Is(err, ErrPostNotVotable) {
+		t.Fatalf("reply vote error = %v", err)
+	}
+}
+
+func TestMemoryPostValidation(t *testing.T) {
+	t.Parallel()
+
+	ctx := context.Background()
+	mem := NewMemory()
+	homeowner := &User{Username: "homeowner", PasswordHash: "hash", Role: RoleUser}
+	if err := mem.CreateUser(ctx, homeowner); err != nil {
+		t.Fatal(err)
+	}
+
+	tests := []struct {
+		name string
+		post *Post
+	}{
+		{
+			name: "root without title",
+			post: &Post{AuthorID: homeowner.ID, Body: "Body"},
+		},
+		{
+			name: "empty parent",
+			post: &Post{ParentID: ptr(""), AuthorID: homeowner.ID, Body: "Body"},
+		},
+		{
+			name: "missing parent",
+			post: &Post{ParentID: ptr("missing"), AuthorID: homeowner.ID, Body: "Body"},
+		},
+		{
+			name: "reply with root fields",
+			post: &Post{
+				ParentID: ptr("missing"),
+				AuthorID: homeowner.ID,
+				Title:    "Not allowed",
+				Body:     "Body",
+			},
+		},
+	}
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			if err := mem.CreatePost(ctx, test.post); !errors.Is(err, ErrInvalidPost) {
+				t.Fatalf("error = %v, want ErrInvalidPost", err)
+			}
+		})
+	}
+
+	hidden := &Post{
+		ID:       "hidden",
+		AuthorID: homeowner.ID,
+		Title:    "Hidden",
+		Body:     "Body",
+		PostDate: "2026-08-26",
+		Hidden:   true,
+	}
+	if err := mem.CreatePost(ctx, hidden); err != nil {
+		t.Fatal(err)
+	}
+	if err := mem.VotePost(ctx, homeowner.ID, hidden.ID, 1); !errors.Is(err, ErrPostNotVotable) {
+		t.Fatalf("hidden root vote error = %v", err)
+	}
+
+	if _, err := mem.GetPostThread(ctx, "missing"); !errors.Is(err, sql.ErrNoRows) {
+		t.Fatalf("missing thread error = %v", err)
+	}
+}
+
+func ptr(value string) *string {
+	return &value
+}

internal/store/postgres_store.go

@@ -144,6 +144,32 @@ func (p *Postgres) UpsertAnswer(ctx context.Context, a *Answer) error {
 	return a.Upsert(ctx)
 }
 
+func (p *Postgres) CreatePost(ctx context.Context, post *Post) error {
+	post.db = p.db
+	return post.Create(ctx)
+}
+
+func (p *Postgres) GetPost(ctx context.Context, id string) (*Post, error) {
+	return GetPost(ctx, p.db, id)
+}
+
+func (p *Postgres) GetPostThread(ctx context.Context, rootID string) (*Post, error) {
+	return GetPostThread(ctx, p.db, rootID)
+}
+
+func (p *Postgres) UpdatePost(ctx context.Context, post *Post) error {
+	post.db = p.db
+	return post.Update(ctx)
+}
+
+func (p *Postgres) ListRootPosts(ctx context.Context, postDate, viewerID string) ([]Post, error) {
+	return ListRootPosts(ctx, p.db, postDate, viewerID)
+}
+
+func (p *Postgres) VotePost(ctx context.Context, userID, postID string, value int) error {
+	return SetPostVote(ctx, p.db, userID, postID, value)
+}
+
 func (p *Postgres) Vote(ctx context.Context, userID, questionID string, value int) error {
 	return Vote(ctx, p.db, userID, questionID, value)
 }

internal/store/sqlc/posts.sql.go

@@ -0,0 +1,355 @@
+// Code generated by sqlc. DO NOT EDIT.
+// versions:
+//   sqlc v1.31.1
+// source: posts.sql
+
+package sqlc
+
+import (
+	"context"
+	"database/sql"
+)
+
+const createPost = `-- name: CreatePost :exec
+INSERT INTO posts (
+  id, parent_id, author_id, title, body, city, post_date, hidden, created_at, updated_at
+)
+VALUES ($1, $2, $3, $4, $5, $6, $7, $8, $9, $10)
+`
+
+type CreatePostParams struct {
+	ID        string
+	ParentID  sql.NullString
+	AuthorID  string
+	Title     string
+	Body      string
+	City      string
+	PostDate  string
+	Hidden    int32
+	CreatedAt string
+	UpdatedAt string
+}
+
+func (q *Queries) CreatePost(ctx context.Context, arg CreatePostParams) error {
+	_, err := q.db.ExecContext(ctx, createPost,
+		arg.ID,
+		arg.ParentID,
+		arg.AuthorID,
+		arg.Title,
+		arg.Body,
+		arg.City,
+		arg.PostDate,
+		arg.Hidden,
+		arg.CreatedAt,
+		arg.UpdatedAt,
+	)
+	return err
+}
+
+const deletePostVote = `-- name: DeletePostVote :exec
+DELETE FROM post_votes
+WHERE user_id = $1 AND post_id = $2
+`
+
+type DeletePostVoteParams struct {
+	UserID string
+	PostID string
+}
+
+func (q *Queries) DeletePostVote(ctx context.Context, arg DeletePostVoteParams) error {
+	_, err := q.db.ExecContext(ctx, deletePostVote, arg.UserID, arg.PostID)
+	return err
+}
+
+const getPost = `-- name: GetPost :one
+SELECT
+  p.id, p.parent_id, p.author_id, u.name AS author_name, u.role AS author_role,
+  p.title, p.body, p.city, p.post_date, p.hidden, p.created_at, p.updated_at
+FROM posts p
+JOIN users u ON u.id = p.author_id
+WHERE p.id = $1
+`
+
+type GetPostRow struct {
+	ID         string
+	ParentID   sql.NullString
+	AuthorID   string
+	AuthorName string
+	AuthorRole string
+	Title      string
+	Body       string
+	City       string
+	PostDate   string
+	Hidden     int32
+	CreatedAt  string
+	UpdatedAt  string
+}
+
+func (q *Queries) GetPost(ctx context.Context, id string) (GetPostRow, error) {
+	row := q.db.QueryRowContext(ctx, getPost, id)
+	var i GetPostRow
+	err := row.Scan(
+		&i.ID,
+		&i.ParentID,
+		&i.AuthorID,
+		&i.AuthorName,
+		&i.AuthorRole,
+		&i.Title,
+		&i.Body,
+		&i.City,
+		&i.PostDate,
+		&i.Hidden,
+		&i.CreatedAt,
+		&i.UpdatedAt,
+	)
+	return i, err
+}
+
+const listPostThread = `-- name: ListPostThread :many
+WITH RECURSIVE thread AS (
+  SELECT p.id, p.parent_id, p.author_id, p.title, p.body, p.city, p.post_date, p.hidden, p.created_at, p.updated_at
+  FROM posts p
+  WHERE p.id = $1 AND p.parent_id IS NULL
+
+  UNION ALL
+
+  SELECT child.id, child.parent_id, child.author_id, child.title, child.body, child.city, child.post_date, child.hidden, child.created_at, child.updated_at
+  FROM posts child
+  JOIN thread parent ON child.parent_id = parent.id
+)
+SELECT
+  thread.id, thread.parent_id, thread.author_id,
+  u.name AS author_name, u.role AS author_role,
+  thread.title, thread.body, thread.city, thread.post_date,
+  thread.hidden, thread.created_at, thread.updated_at
+FROM thread
+JOIN users u ON u.id = thread.author_id
+ORDER BY thread.created_at, thread.id
+`
+
+type ListPostThreadRow struct {
+	ID         string
+	ParentID   sql.NullString
+	AuthorID   string
+	AuthorName string
+	AuthorRole string
+	Title      string
+	Body       string
+	City       string
+	PostDate   string
+	Hidden     int32
+	CreatedAt  string
+	UpdatedAt  string
+}
+
+func (q *Queries) ListPostThread(ctx context.Context, id string) ([]ListPostThreadRow, error) {
+	rows, err := q.db.QueryContext(ctx, listPostThread, id)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	items := []ListPostThreadRow{}
+	for rows.Next() {
+		var i ListPostThreadRow
+		if err := rows.Scan(
+			&i.ID,
+			&i.ParentID,
+			&i.AuthorID,
+			&i.AuthorName,
+			&i.AuthorRole,
+			&i.Title,
+			&i.Body,
+			&i.City,
+			&i.PostDate,
+			&i.Hidden,
+			&i.CreatedAt,
+			&i.UpdatedAt,
+		); err != nil {
+			return nil, err
+		}
+		items = append(items, i)
+	}
+	if err := rows.Close(); err != nil {
+		return nil, err
+	}
+	if err := rows.Err(); err != nil {
+		return nil, err
+	}
+	return items, nil
+}
+
+const listRootPosts = `-- name: ListRootPosts :many
+WITH RECURSIVE roots AS (
+  SELECT p.id, p.parent_id, p.author_id, p.title, p.body, p.city, p.post_date, p.hidden, p.created_at, p.updated_at
+  FROM posts p
+  WHERE p.parent_id IS NULL
+    AND p.post_date = $3
+    AND p.hidden = 0
+),
+thread AS (
+  SELECT roots.id AS root_id, roots.id AS post_id, roots.author_id
+  FROM roots
+
+  UNION ALL
+
+  SELECT thread.root_id, child.id, child.author_id
+  FROM thread
+  JOIN posts child ON child.parent_id = thread.post_id
+),
+answered AS (
+  SELECT thread.root_id, bool_or(u.role = 'admin' AND thread.post_id <> thread.root_id) AS answered
+  FROM thread
+  JOIN users u ON u.id = thread.author_id
+  GROUP BY thread.root_id
+),
+scores AS (
+  SELECT post_id, COALESCE(SUM(value), 0)::bigint AS score
+  FROM post_votes
+  GROUP BY post_id
+)
+SELECT
+  roots.id, roots.parent_id, roots.author_id,
+  u.name AS author_name, u.role AS author_role,
+  roots.title, roots.body, roots.city, roots.post_date,
+  roots.hidden, roots.created_at, roots.updated_at,
+  COALESCE(scores.score, 0)::bigint AS score,
+  COALESCE(answered.answered, false)::bool AS answered,
+  COALESCE((
+    SELECT post_votes.value
+    FROM post_votes
+    WHERE post_votes.user_id = $1
+      AND post_votes.post_id = roots.id
+  ), 0)::bigint AS user_vote
+FROM roots
+JOIN users u ON u.id = roots.author_id
+LEFT JOIN scores ON scores.post_id = roots.id
+LEFT JOIN answered ON answered.root_id = roots.id
+ORDER BY score DESC, roots.created_at, roots.id
+LIMIT $2
+`
+
+type ListRootPostsParams struct {
+	ViewerID string
+	RowLimit int32
+	PostDate string
+}
+
+type ListRootPostsRow struct {
+	ID         string
+	ParentID   sql.NullString
+	AuthorID   string
+	AuthorName string
+	AuthorRole string
+	Title      string
+	Body       string
+	City       string
+	PostDate   string
+	Hidden     int32
+	CreatedAt  string
+	UpdatedAt  string
+	Score      int64
+	Answered   bool
+	UserVote   int64
+}
+
+func (q *Queries) ListRootPosts(ctx context.Context, arg ListRootPostsParams) ([]ListRootPostsRow, error) {
+	rows, err := q.db.QueryContext(ctx, listRootPosts, arg.ViewerID, arg.RowLimit, arg.PostDate)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	items := []ListRootPostsRow{}
+	for rows.Next() {
+		var i ListRootPostsRow
+		if err := rows.Scan(
+			&i.ID,
+			&i.ParentID,
+			&i.AuthorID,
+			&i.AuthorName,
+			&i.AuthorRole,
+			&i.Title,
+			&i.Body,
+			&i.City,
+			&i.PostDate,
+			&i.Hidden,
+			&i.CreatedAt,
+			&i.UpdatedAt,
+			&i.Score,
+			&i.Answered,
+			&i.UserVote,
+		); err != nil {
+			return nil, err
+		}
+		items = append(items, i)
+	}
+	if err := rows.Close(); err != nil {
+		return nil, err
+	}
+	if err := rows.Err(); err != nil {
+		return nil, err
+	}
+	return items, nil
+}
+
+const postIsVisibleRoot = `-- name: PostIsVisibleRoot :one
+SELECT EXISTS(
+  SELECT 1
+  FROM posts
+  WHERE id = $1 AND parent_id IS NULL AND hidden = 0
+)::bool
+`
+
+func (q *Queries) PostIsVisibleRoot(ctx context.Context, id string) (bool, error) {
+	row := q.db.QueryRowContext(ctx, postIsVisibleRoot, id)
+	var column_1 bool
+	err := row.Scan(&column_1)
+	return column_1, err
+}
+
+const updatePost = `-- name: UpdatePost :execrows
+UPDATE posts
+SET body = $2, updated_at = $3
+WHERE id = $1
+`
+
+type UpdatePostParams struct {
+	ID        string
+	Body      string
+	UpdatedAt string
+}
+
+func (q *Queries) UpdatePost(ctx context.Context, arg UpdatePostParams) (int64, error) {
+	result, err := q.db.ExecContext(ctx, updatePost, arg.ID, arg.Body, arg.UpdatedAt)
+	if err != nil {
+		return 0, err
+	}
+	return result.RowsAffected()
+}
+
+const upsertPostVoteOnVisibleRoot = `-- name: UpsertPostVoteOnVisibleRoot :execrows
+INSERT INTO post_votes (user_id, post_id, value)
+SELECT $1, $2, $3
+FROM posts p
+WHERE p.id = $2 AND p.parent_id IS NULL AND p.hidden = 0
+ON CONFLICT (user_id, post_id) DO UPDATE
+SET value = excluded.value
+WHERE EXISTS (
+  SELECT 1
+  FROM posts p2
+  WHERE p2.id = excluded.post_id AND p2.parent_id IS NULL AND p2.hidden = 0
+)
+`
+
+type UpsertPostVoteOnVisibleRootParams struct {
+	UserID string
+	PostID string
+	Value  int32
+}
+
+func (q *Queries) UpsertPostVoteOnVisibleRoot(ctx context.Context, arg UpsertPostVoteOnVisibleRootParams) (int64, error) {
+	result, err := q.db.ExecContext(ctx, upsertPostVoteOnVisibleRoot, arg.UserID, arg.PostID, arg.Value)
+	if err != nil {
+		return 0, err
+	}
+	return result.RowsAffected()
+}

internal/store/store.go

@@ -37,6 +37,13 @@ type Store interface {
 	GetAnswer(ctx context.Context, questionID string) (*Answer, error)
 	UpsertAnswer(ctx context.Context, a *Answer) error
 
+	CreatePost(ctx context.Context, post *Post) error
+	GetPost(ctx context.Context, id string) (*Post, error)
+	GetPostThread(ctx context.Context, rootID string) (*Post, error)
+	UpdatePost(ctx context.Context, post *Post) error
+	ListRootPosts(ctx context.Context, postDate, viewerID string) ([]Post, error)
+	VotePost(ctx context.Context, userID, postID string, value int) error
+
 	// Vote sets the vote to 1, -1, or 0 (clear) on a visible question.
 	Vote(ctx context.Context, userID, questionID string, value int) error
 }