coder · ibetitsmike · Jul 29, 2026 · Jul 25, 2026 · Jul 28, 2026 · Jul 28, 2026
diff --git a/coderd/database/dbauthz/dbauthz.go b/coderd/database/dbauthz/dbauthz.go
@@ -6086,7 +6086,7 @@ func (q *querier) InsertChatFile(ctx context.Context, arg database.InsertChatFil
 	return insert(q.log, q.auth, rbac.ResourceChat.WithOwner(arg.OwnerID.String()).InOrg(arg.OrganizationID), q.db.InsertChatFile)(ctx, arg)
 }
 
-func (q *querier) InsertChatMessages(ctx context.Context, arg database.InsertChatMessagesParams) ([]database.ChatMessage, error) {
+func (q *querier) InsertChatMessages(ctx context.Context, arg database.InsertChatMessagesParams) ([]database.InsertChatMessagesRow, error) {
 	// Authorize create on the parent chat (using update permission).
 	chat, err := q.db.GetChatByID(ctx, arg.ChatID)
 	if err != nil {

diff --git a/coderd/database/dbauthz/dbauthz_test.go b/coderd/database/dbauthz/dbauthz_test.go
@@ -1281,7 +1281,7 @@ func (s *MethodTestSuite) TestChats() {
 	s.Run("InsertChatMessages", s.Mocked(func(dbm *dbmock.MockStore, faker *gofakeit.Faker, check *expects) {
 		chat := testutil.Fake(s.T(), faker, database.Chat{})
 		arg := testutil.Fake(s.T(), faker, database.InsertChatMessagesParams{ChatID: chat.ID})
-		msgs := []database.ChatMessage{testutil.Fake(s.T(), faker, database.ChatMessage{ChatID: chat.ID})}
+		msgs := []database.InsertChatMessagesRow{testutil.Fake(s.T(), faker, database.InsertChatMessagesRow{ChatID: chat.ID})}
 		dbm.EXPECT().GetChatByID(gomock.Any(), chat.ID).Return(chat, nil).AnyTimes()
 		dbm.EXPECT().InsertChatMessages(gomock.Any(), arg).Return(msgs, nil).AnyTimes()
 		check.Args(arg).Asserts(chat, policy.ActionUpdate).Returns(msgs)

diff --git a/coderd/database/dbgen/dbgen.go b/coderd/database/dbgen/dbgen.go
@@ -145,7 +145,7 @@ func ChatMessage(t testing.TB, db database.Store, seed database.ChatMessage) dat
 	})
 	require.NoError(t, err, "insert chat message")
 	require.Len(t, msgs, 1)
-	return msgs[0]
+	return database.ChatMessage(msgs[0])
 }
 
 const (

diff --git a/coderd/database/dbmetrics/querymetrics.go b/coderd/database/dbmetrics/querymetrics.go
diff --git a/coderd/database/dbmock/dbmock.go b/coderd/database/dbmock/dbmock.go
diff --git a/coderd/database/dump.sql b/coderd/database/dump.sql
diff --git a/coderd/database/migrations/000559_chat_messages_last_by_role_index.down.sql b/coderd/database/migrations/000559_chat_messages_last_by_role_index.down.sql
@@ -0,0 +1 @@
+DROP INDEX IF EXISTS idx_chat_messages_chat_role_id;
diff --git a/coderd/database/migrations/000559_chat_messages_last_by_role_index.up.sql b/coderd/database/migrations/000559_chat_messages_last_by_role_index.up.sql
@@ -0,0 +1,5 @@
+-- Serves GetLastChatMessageByRole. It orders by id, so the existing
+-- (chat_id, created_at) index cannot supply the LIMIT 1 row in index order.
+CREATE INDEX idx_chat_messages_chat_role_id
+    ON chat_messages (chat_id, role, id DESC)
+    WHERE deleted = false;
diff --git a/coderd/database/modelqueries_internal_test.go b/coderd/database/modelqueries_internal_test.go
@@ -1,6 +1,7 @@
 package database
 
 import (
+	"reflect"
 	"regexp"
 	"slices"
 	"strings"
@@ -168,6 +169,27 @@ func TestFinalizeStaleChatDebugRows_TerminalStatusAlignment(t *testing.T) {
 	}
 }
 
+// TestInsertChatMessagesOrderContract guards the input-order guarantee that
+// callers rely on when indexing the returned slice. A behavior test cannot:
+// Postgres evaluates the id default in row order anyway, so a batch still looks
+// ordered once the guarantee is removed.
+func TestInsertChatMessagesOrderContract(t *testing.T) {
+	t.Parallel()
+
+	require.Contains(t, insertChatMessages, "nextval('chat_messages_id_seq')",
+		"ids must be allocated explicitly so they can be correlated to input array position")
+	require.Contains(t, insertChatMessages, "ROW_NUMBER() OVER (ORDER BY id)",
+		"the k-th smallest allocated id must be assigned to input index k")
+	require.Regexp(t, `(?s)ORDER BY id\s*\z`, strings.TrimSpace(insertChatMessages),
+		"returned rows must be explicitly ordered by id rather than relying on RETURNING order")
+
+	// Every parallel input array must be read at the allocated ordinal. A column
+	// left on UNNEST would be positioned by the executor instead.
+	subscripted := regexp.MustCompile(`\)\[allocated\.ord\]`).FindAllString(insertChatMessages, -1)
+	require.Len(t, subscripted, reflect.TypeOf(InsertChatMessagesParams{}).NumField()-1,
+		"each InsertChatMessagesParams array field, all but ChatID, must be subscripted by allocated.ord")
+}
+
 // extractWhereClause extracts the WHERE clause from a SQL query string
 func extractWhereClause(query string) string {
 	// Find WHERE and get everything after it

diff --git a/coderd/database/querier.go b/coderd/database/querier.go
diff --git a/coderd/database/querier_test.go b/coderd/database/querier_test.go
@@ -12212,6 +12212,135 @@ func TestInsertChatMessages(t *testing.T) {
 	})
 }
 
+// The returned ids are in insert order, which the inverted created_at values
+// deliberately contradict.
+func insertChatMessagesInvertedTimestamps(t *testing.T, db database.Store, sqlDB *sql.DB, roles []database.ChatMessageRole) (database.Chat, []int64) {
+	t.Helper()
+
+	ctx := context.Background()
+	org := dbgen.Organization(t, db, database.Organization{})
+	owner := dbgen.User(t, db, database.User{})
+	modelCfg := dbgen.ChatModelConfig(t, db, database.ChatModelConfig{
+		CreatedBy: uuid.NullUUID{UUID: owner.ID, Valid: true},
+		UpdatedBy: uuid.NullUUID{UUID: owner.ID, Valid: true},
+	})
+	chat := dbgen.Chat(t, db, database.Chat{
+		OrganizationID:    org.ID,
+		OwnerID:           owner.ID,
+		LastModelConfigID: modelCfg.ID,
+	})
+
+	count := len(roles)
+	inserted, err := db.InsertChatMessages(ctx, database.InsertChatMessagesParams{
+		ChatID:              chat.ID,
+		CreatedBy:           slices.Repeat([]uuid.UUID{owner.ID}, count),
+		ModelConfigID:       slices.Repeat([]uuid.UUID{modelCfg.ID}, count),
+		Role:                roles,
+		ContentVersion:      slices.Repeat([]int16{chatprompt.CurrentContentVersion}, count),
+		Visibility:          slices.Repeat([]database.ChatMessageVisibility{database.ChatMessageVisibilityBoth}, count),
+		Content:             slices.Repeat([]string{`"message"`}, count),
+		InputTokens:         make([]int64, count),
+		OutputTokens:        make([]int64, count),
+		TotalTokens:         make([]int64, count),
+		ReasoningTokens:     make([]int64, count),
+		CacheCreationTokens: make([]int64, count),
+		CacheReadTokens:     make([]int64, count),
+		ContextLimit:        make([]int64, count),
+		Compressed:          make([]bool, count),
+		TotalCostMicros:     make([]int64, count),
+		RuntimeMs:           make([]int64, count),
+	})
+	require.NoError(t, err)
+	require.Len(t, inserted, count)
+
+	insertedIDs := make([]int64, count)
+	for i, message := range inserted {
+		insertedIDs[i] = message.ID
+		_, err := sqlDB.ExecContext(ctx,
+			"UPDATE chat_messages SET created_at = $1 WHERE id = $2",
+			message.CreatedAt.Add(time.Duration(count-i)*time.Minute), message.ID)
+		require.NoError(t, err)
+	}
+
+	return chat, insertedIDs
+}
+
+func chatMessageIDs(messages []database.ChatMessage) []int64 {
+	ids := make([]int64, len(messages))
+	for i, message := range messages {
+		ids[i] = message.ID
+	}
+	return ids
+}
+
+func TestGetChatMessagesByChatIDOrdersByID(t *testing.T) {
+	t.Parallel()
+
+	db, _, sqlDB := dbtestutil.NewDBWithSQLDB(t)
+	ctx := context.Background()
+
+	chat, insertedIDs := insertChatMessagesInvertedTimestamps(t, db, sqlDB,
+		slices.Repeat([]database.ChatMessageRole{database.ChatMessageRoleUser}, 3))
+
+	messages, err := db.GetChatMessagesByChatID(ctx, database.GetChatMessagesByChatIDParams{
+		ChatID:  chat.ID,
+		AfterID: 0,
+	})
+	require.NoError(t, err)
+	require.Equal(t, insertedIDs, chatMessageIDs(messages))
+}
+
+func TestGetChatMessagesByRevisionForStreamOrdersByID(t *testing.T) {
+	t.Parallel()
+
+	db, _, sqlDB := dbtestutil.NewDBWithSQLDB(t)
+	ctx := context.Background()
+
+	chat, insertedIDs := insertChatMessagesInvertedTimestamps(t, db, sqlDB,
+		slices.Repeat([]database.ChatMessageRole{database.ChatMessageRoleUser}, 3))
+
+	messages, err := db.GetChatMessagesByRevisionForStream(ctx, database.GetChatMessagesByRevisionForStreamParams{
+		ChatID:        chat.ID,
+		AfterRevision: 0,
+	})
+	require.NoError(t, err)
+	require.Equal(t, insertedIDs, chatMessageIDs(messages))
+}
+
+func TestGetLastChatMessageByRoleOrdersByID(t *testing.T) {
+	t.Parallel()
+
+	db, _, sqlDB := dbtestutil.NewDBWithSQLDB(t)
+	ctx := context.Background()
+
+	chat, insertedIDs := insertChatMessagesInvertedTimestamps(t, db, sqlDB,
+		slices.Repeat([]database.ChatMessageRole{database.ChatMessageRoleAssistant}, 3))
+
+	last, err := db.GetLastChatMessageByRole(ctx, database.GetLastChatMessageByRoleParams{
+		ChatID: chat.ID,
+		Role:   database.ChatMessageRoleAssistant,
+	})
+	require.NoError(t, err)
+	require.Equal(t, insertedIDs[len(insertedIDs)-1], last.ID)
+}
+
+// Sequence cache blocks are handed out per session, so above cache 1 a backend
+// holding stale cached values can take the chat row lock second and still commit
+// lower ids. Bumping a sequence cache is an ordinary throughput tweak.
+func TestChatMessagesSequenceCacheIsOne(t *testing.T) {
+	t.Parallel()
+
+	_, _, sqlDB := dbtestutil.NewDBWithSQLDB(t)
+	ctx := context.Background()
+
+	var cacheSize int64
+	err := sqlDB.QueryRowContext(ctx,
+		"SELECT cache_size FROM pg_sequences WHERE sequencename = 'chat_messages_id_seq'").
+		Scan(&cacheSize)
+	require.NoError(t, err)
+	require.Equal(t, int64(1), cacheSize, "chat_messages_id_seq must use cache 1")
+}
+
 func TestGetChatMessagesForPromptByChatID(t *testing.T) {
 	t.Parallel()
 
@@ -12294,7 +12423,7 @@ func TestGetChatMessagesForPromptByChatID(t *testing.T) {
 			RuntimeMs:           []int64{0},
 		})
 		require.NoError(t, err)
-		return results[0]
+		return database.ChatMessage(results[0])
 	}
 
 	msgIDs := func(msgs []database.ChatMessage) []int64 {
@@ -17173,7 +17302,7 @@ func TestGetChatsSearch(t *testing.T) {
 		})
 		require.NoError(t, err)
 		require.Len(t, msgs, 1)
-		return msgs[0]
+		return database.ChatMessage(msgs[0])
 	}
 
 	linkPR := func(chatID uuid.UUID, url, state, prTitle string, prNumber int32, gitRemoteOrigin string) {
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1 @@
		DROP INDEX IF EXISTS idx_chat_messages_chat_role_id;