feat: add last_injected_context column to chats table (#23798)

Adds a nullable JSONB column `last_injected_context` to the `chats`
table that stores the most recently persisted injected context parts
(AGENTS.md context-file and skill message parts). The column is updated
only when `persistInstructionFiles()` runs — on first workspace attach
or when the agent changes — so there are no redundant writes on
subsequent turns.

Internal fields (`ContextFileContent`, `ContextFileOS`,
`ContextFileDirectory`, `SkillDir`) are stripped at write time so the
column only holds small metadata. No stripping needed on the read path.

<details>
<summary>Implementation notes</summary>

- New migration `000456` adds nullable `last_injected_context JSONB`
column.
- New SQL query `UpdateChatLastInjectedContext` writes the column
without touching `updated_at`.
- `persistInstructionFiles()` strips internal fields from parts via
`StripInternal()` before persisting.
- Sentinel path (no AGENTS.md) persists skill-only parts when skills
exist.
- `codersdk.Chat` exposes `LastInjectedContext []ChatMessagePart`
(omitempty).
- `db2sdk.Chat()` passes through the already-clean data.

</details>

coderd/database/db2sdk/db2sdk.go

@@ -1572,6 +1572,17 @@ func Chat(c database.Chat, diffStatus *database.ChatDiffStatus) codersdk.Chat {
 		convertedDiffStatus := ChatDiffStatus(c.ID, diffStatus)
 		chat.DiffStatus = &convertedDiffStatus
 	}
+	if c.LastInjectedContext.Valid {
+		var parts []codersdk.ChatMessagePart
+		// Internal fields are stripped at write time in
+		// chatd.updateLastInjectedContext, so no
+		// StripInternal call is needed here. Unmarshal
+		// errors are suppressed — the column is written by
+		// us with a known schema.
+		if err := json.Unmarshal(c.LastInjectedContext.RawMessage, &parts); err == nil {
+			chat.LastInjectedContext = parts
+		}
+	}
 	return chat
 }
 

coderd/database/db2sdk/db2sdk_test.go

@@ -541,6 +541,13 @@ func TestChat_AllFieldsPopulated(t *testing.T) {
 		PinOrder:          1,
 		MCPServerIDs:      []uuid.UUID{uuid.New()},
 		Labels:            database.StringMap{"env": "prod"},
+		LastInjectedContext: pqtype.NullRawMessage{
+			// Use a context-file part to verify internal
+			// fields are not present (they are stripped at
+			// write time by chatd, not at read time).
+			RawMessage: json.RawMessage(`[{"type":"context-file","context_file_path":"/AGENTS.md"}]`),
+			Valid:      true,
+		},
 	}
 	// Only ChatID is needed here. This test checks that
 	// Chat.DiffStatus is non-nil, not that every DiffStatus

coderd/database/dbauthz/dbauthz.go

@@ -5752,6 +5752,17 @@ func (q *querier) UpdateChatLabelsByID(ctx context.Context, arg database.UpdateC
 	return q.db.UpdateChatLabelsByID(ctx, arg)
 }
 
+func (q *querier) UpdateChatLastInjectedContext(ctx context.Context, arg database.UpdateChatLastInjectedContextParams) (database.Chat, error) {
+	chat, err := q.db.GetChatByID(ctx, arg.ID)
+	if err != nil {
+		return database.Chat{}, err
+	}
+	if err := q.authorizeContext(ctx, policy.ActionUpdate, chat); err != nil {
+		return database.Chat{}, err
+	}
+	return q.db.UpdateChatLastInjectedContext(ctx, arg)
+}
+
 func (q *querier) UpdateChatLastModelConfigByID(ctx context.Context, arg database.UpdateChatLastModelConfigByIDParams) (database.Chat, error) {
 	chat, err := q.db.GetChatByID(ctx, arg.ID)
 	if err != nil {

coderd/database/dbauthz/dbauthz_test.go

@@ -1204,6 +1204,19 @@ func (s *MethodTestSuite) TestChats() {
 		dbm.EXPECT().UpdateChatMCPServerIDs(gomock.Any(), arg).Return(chat, nil).AnyTimes()
 		check.Args(arg).Asserts(chat, policy.ActionUpdate).Returns(chat)
 	}))
+	s.Run("UpdateChatLastInjectedContext", s.Mocked(func(dbm *dbmock.MockStore, faker *gofakeit.Faker, check *expects) {
+		chat := testutil.Fake(s.T(), faker, database.Chat{})
+		arg := database.UpdateChatLastInjectedContextParams{
+			ID: chat.ID,
+			LastInjectedContext: pqtype.NullRawMessage{
+				RawMessage: json.RawMessage(`[{"type":"text","text":"test"}]`),
+				Valid:      true,
+			},
+		}
+		dbm.EXPECT().GetChatByID(gomock.Any(), chat.ID).Return(chat, nil).AnyTimes()
+		dbm.EXPECT().UpdateChatLastInjectedContext(gomock.Any(), arg).Return(chat, nil).AnyTimes()
+		check.Args(arg).Asserts(chat, policy.ActionUpdate).Returns(chat)
+	}))
 	s.Run("UpdateChatLastReadMessageID", s.Mocked(func(dbm *dbmock.MockStore, faker *gofakeit.Faker, check *expects) {
 		chat := testutil.Fake(s.T(), faker, database.Chat{})
 		arg := database.UpdateChatLastReadMessageIDParams{

coderd/database/dbmetrics/querymetrics.go

@@ -4112,6 +4112,14 @@ func (m queryMetricsStore) UpdateChatLabelsByID(ctx context.Context, arg databas
 	return r0, r1
 }
 
+func (m queryMetricsStore) UpdateChatLastInjectedContext(ctx context.Context, arg database.UpdateChatLastInjectedContextParams) (database.Chat, error) {
+	start := time.Now()
+	r0, r1 := m.s.UpdateChatLastInjectedContext(ctx, arg)
+	m.queryLatencies.WithLabelValues("UpdateChatLastInjectedContext").Observe(time.Since(start).Seconds())
+	m.queryCounts.WithLabelValues(httpmw.ExtractHTTPRoute(ctx), httpmw.ExtractHTTPMethod(ctx), "UpdateChatLastInjectedContext").Inc()
+	return r0, r1
+}
+
 func (m queryMetricsStore) UpdateChatLastModelConfigByID(ctx context.Context, arg database.UpdateChatLastModelConfigByIDParams) (database.Chat, error) {
 	start := time.Now()
 	r0, r1 := m.s.UpdateChatLastModelConfigByID(ctx, arg)

coderd/database/dbmock/dbmock.go

@@ -7790,6 +7790,21 @@ func (mr *MockStoreMockRecorder) UpdateChatLabelsByID(ctx, arg any) *gomock.Call
 	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "UpdateChatLabelsByID", reflect.TypeOf((*MockStore)(nil).UpdateChatLabelsByID), ctx, arg)
 }
 
+// UpdateChatLastInjectedContext mocks base method.
+func (m *MockStore) UpdateChatLastInjectedContext(ctx context.Context, arg database.UpdateChatLastInjectedContextParams) (database.Chat, error) {
+	m.ctrl.T.Helper()
+	ret := m.ctrl.Call(m, "UpdateChatLastInjectedContext", ctx, arg)
+	ret0, _ := ret[0].(database.Chat)
+	ret1, _ := ret[1].(error)
+	return ret0, ret1
+}
+
+// UpdateChatLastInjectedContext indicates an expected call of UpdateChatLastInjectedContext.
+func (mr *MockStoreMockRecorder) UpdateChatLastInjectedContext(ctx, arg any) *gomock.Call {
+	mr.mock.ctrl.T.Helper()
+	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "UpdateChatLastInjectedContext", reflect.TypeOf((*MockStore)(nil).UpdateChatLastInjectedContext), ctx, arg)
+}
+
 // UpdateChatLastModelConfigByID mocks base method.
 func (m *MockStore) UpdateChatLastModelConfigByID(ctx context.Context, arg database.UpdateChatLastModelConfigByIDParams) (database.Chat, error) {
 	m.ctrl.T.Helper()

coderd/database/dump.sql

@@ -1403,7 +1403,8 @@ CREATE TABLE chats (
     build_id uuid,
     agent_id uuid,
     pin_order integer DEFAULT 0 NOT NULL,
-    last_read_message_id bigint
+    last_read_message_id bigint,
+    last_injected_context jsonb
 );
 
 CREATE TABLE connection_logs (

coderd/database/migrations/000456_chat_last_injected_context.down.sql

@@ -0,0 +1 @@
+ALTER TABLE chats DROP COLUMN last_injected_context;

coderd/database/migrations/000456_chat_last_injected_context.up.sql

@@ -0,0 +1 @@
+ALTER TABLE chats ADD COLUMN last_injected_context JSONB;

coderd/database/modelqueries.go

@@ -795,6 +795,7 @@ func (q *sqlQuerier) GetAuthorizedChats(ctx context.Context, arg GetChatsParams,
 			&i.Chat.AgentID,
 			&i.Chat.PinOrder,
 			&i.Chat.LastReadMessageID,
+			&i.Chat.LastInjectedContext,
 			&i.HasUnread); err != nil {
 			return nil, err
 		}

coderd/database/models.go

@@ -4153,28 +4153,29 @@ type BoundaryUsageStat struct {
 }
 
 type Chat struct {
-	ID                uuid.UUID      `db:"id" json:"id"`
-	OwnerID           uuid.UUID      `db:"owner_id" json:"owner_id"`
-	WorkspaceID       uuid.NullUUID  `db:"workspace_id" json:"workspace_id"`
-	Title             string         `db:"title" json:"title"`
-	Status            ChatStatus     `db:"status" json:"status"`
-	WorkerID          uuid.NullUUID  `db:"worker_id" json:"worker_id"`
-	StartedAt         sql.NullTime   `db:"started_at" json:"started_at"`
-	HeartbeatAt       sql.NullTime   `db:"heartbeat_at" json:"heartbeat_at"`
-	CreatedAt         time.Time      `db:"created_at" json:"created_at"`
-	UpdatedAt         time.Time      `db:"updated_at" json:"updated_at"`
-	ParentChatID      uuid.NullUUID  `db:"parent_chat_id" json:"parent_chat_id"`
-	RootChatID        uuid.NullUUID  `db:"root_chat_id" json:"root_chat_id"`
-	LastModelConfigID uuid.UUID      `db:"last_model_config_id" json:"last_model_config_id"`
-	Archived          bool           `db:"archived" json:"archived"`
-	LastError         sql.NullString `db:"last_error" json:"last_error"`
-	Mode              NullChatMode   `db:"mode" json:"mode"`
-	MCPServerIDs      []uuid.UUID    `db:"mcp_server_ids" json:"mcp_server_ids"`
-	Labels            StringMap      `db:"labels" json:"labels"`
-	BuildID           uuid.NullUUID  `db:"build_id" json:"build_id"`
-	AgentID           uuid.NullUUID  `db:"agent_id" json:"agent_id"`
-	PinOrder          int32          `db:"pin_order" json:"pin_order"`
-	LastReadMessageID sql.NullInt64  `db:"last_read_message_id" json:"last_read_message_id"`
+	ID                  uuid.UUID             `db:"id" json:"id"`
+	OwnerID             uuid.UUID             `db:"owner_id" json:"owner_id"`
+	WorkspaceID         uuid.NullUUID         `db:"workspace_id" json:"workspace_id"`
+	Title               string                `db:"title" json:"title"`
+	Status              ChatStatus            `db:"status" json:"status"`
+	WorkerID            uuid.NullUUID         `db:"worker_id" json:"worker_id"`
+	StartedAt           sql.NullTime          `db:"started_at" json:"started_at"`
+	HeartbeatAt         sql.NullTime          `db:"heartbeat_at" json:"heartbeat_at"`
+	CreatedAt           time.Time             `db:"created_at" json:"created_at"`
+	UpdatedAt           time.Time             `db:"updated_at" json:"updated_at"`
+	ParentChatID        uuid.NullUUID         `db:"parent_chat_id" json:"parent_chat_id"`
+	RootChatID          uuid.NullUUID         `db:"root_chat_id" json:"root_chat_id"`
+	LastModelConfigID   uuid.UUID             `db:"last_model_config_id" json:"last_model_config_id"`
+	Archived            bool                  `db:"archived" json:"archived"`
+	LastError           sql.NullString        `db:"last_error" json:"last_error"`
+	Mode                NullChatMode          `db:"mode" json:"mode"`
+	MCPServerIDs        []uuid.UUID           `db:"mcp_server_ids" json:"mcp_server_ids"`
+	Labels              StringMap             `db:"labels" json:"labels"`
+	BuildID             uuid.NullUUID         `db:"build_id" json:"build_id"`
+	AgentID             uuid.NullUUID         `db:"agent_id" json:"agent_id"`
+	PinOrder            int32                 `db:"pin_order" json:"pin_order"`
+	LastReadMessageID   sql.NullInt64         `db:"last_read_message_id" json:"last_read_message_id"`
+	LastInjectedContext pqtype.NullRawMessage `db:"last_injected_context" json:"last_injected_context"`
 }
 
 type ChatDiffStatus struct {

coderd/database/querier.go

@@ -854,6 +854,11 @@ type sqlcQuerier interface {
 	// replicas know the worker is still alive.
 	UpdateChatHeartbeat(ctx context.Context, arg UpdateChatHeartbeatParams) (int64, error)
 	UpdateChatLabelsByID(ctx context.Context, arg UpdateChatLabelsByIDParams) (Chat, error)
+	// Updates the cached injected context parts (AGENTS.md +
+	// skills) on the chat row. Called only when context changes
+	// (first workspace attach or agent change). updated_at is
+	// intentionally not touched to avoid reordering the chat list.
+	UpdateChatLastInjectedContext(ctx context.Context, arg UpdateChatLastInjectedContextParams) (Chat, error)
 	UpdateChatLastModelConfigByID(ctx context.Context, arg UpdateChatLastModelConfigByIDParams) (Chat, error)
 	// Updates the last read message ID for a chat. This is used to track
 	// which messages the owner has seen, enabling unread indicators.

coderd/database/queries.sql.go

@@ -4065,7 +4065,7 @@ WHERE
             $3::int
     )
 RETURNING
-    id, owner_id, workspace_id, title, status, worker_id, started_at, heartbeat_at, created_at, updated_at, parent_chat_id, root_chat_id, last_model_config_id, archived, last_error, mode, mcp_server_ids, labels, build_id, agent_id, pin_order, last_read_message_id
+    id, owner_id, workspace_id, title, status, worker_id, started_at, heartbeat_at, created_at, updated_at, parent_chat_id, root_chat_id, last_model_config_id, archived, last_error, mode, mcp_server_ids, labels, build_id, agent_id, pin_order, last_read_message_id, last_injected_context
 `
 
 type AcquireChatsParams struct {
@@ -4108,6 +4108,7 @@ func (q *sqlQuerier) AcquireChats(ctx context.Context, arg AcquireChatsParams) (
 			&i.AgentID,
 			&i.PinOrder,
 			&i.LastReadMessageID,
+			&i.LastInjectedContext,
 		); err != nil {
 			return nil, err
 		}
@@ -4341,7 +4342,7 @@ func (q *sqlQuerier) DeleteChatUsageLimitUserOverride(ctx context.Context, userI
 
 const getChatByID = `-- name: GetChatByID :one
 SELECT
-    id, owner_id, workspace_id, title, status, worker_id, started_at, heartbeat_at, created_at, updated_at, parent_chat_id, root_chat_id, last_model_config_id, archived, last_error, mode, mcp_server_ids, labels, build_id, agent_id, pin_order, last_read_message_id
+    id, owner_id, workspace_id, title, status, worker_id, started_at, heartbeat_at, created_at, updated_at, parent_chat_id, root_chat_id, last_model_config_id, archived, last_error, mode, mcp_server_ids, labels, build_id, agent_id, pin_order, last_read_message_id, last_injected_context
 FROM
     chats
 WHERE
@@ -4374,12 +4375,13 @@ func (q *sqlQuerier) GetChatByID(ctx context.Context, id uuid.UUID) (Chat, error
 		&i.AgentID,
 		&i.PinOrder,
 		&i.LastReadMessageID,
+		&i.LastInjectedContext,
 	)
 	return i, err
 }
 
 const getChatByIDForUpdate = `-- name: GetChatByIDForUpdate :one
-SELECT id, owner_id, workspace_id, title, status, worker_id, started_at, heartbeat_at, created_at, updated_at, parent_chat_id, root_chat_id, last_model_config_id, archived, last_error, mode, mcp_server_ids, labels, build_id, agent_id, pin_order, last_read_message_id FROM chats WHERE id = $1::uuid FOR UPDATE
+SELECT id, owner_id, workspace_id, title, status, worker_id, started_at, heartbeat_at, created_at, updated_at, parent_chat_id, root_chat_id, last_model_config_id, archived, last_error, mode, mcp_server_ids, labels, build_id, agent_id, pin_order, last_read_message_id, last_injected_context FROM chats WHERE id = $1::uuid FOR UPDATE
 `
 
 func (q *sqlQuerier) GetChatByIDForUpdate(ctx context.Context, id uuid.UUID) (Chat, error) {
@@ -4408,6 +4410,7 @@ func (q *sqlQuerier) GetChatByIDForUpdate(ctx context.Context, id uuid.UUID) (Ch
 		&i.AgentID,
 		&i.PinOrder,
 		&i.LastReadMessageID,
+		&i.LastInjectedContext,
 	)
 	return i, err
 }
@@ -5319,7 +5322,7 @@ func (q *sqlQuerier) GetChatUsageLimitUserOverride(ctx context.Context, userID u
 
 const getChats = `-- name: GetChats :many
 SELECT
-    chats.id, chats.owner_id, chats.workspace_id, chats.title, chats.status, chats.worker_id, chats.started_at, chats.heartbeat_at, chats.created_at, chats.updated_at, chats.parent_chat_id, chats.root_chat_id, chats.last_model_config_id, chats.archived, chats.last_error, chats.mode, chats.mcp_server_ids, chats.labels, chats.build_id, chats.agent_id, chats.pin_order, chats.last_read_message_id,
+    chats.id, chats.owner_id, chats.workspace_id, chats.title, chats.status, chats.worker_id, chats.started_at, chats.heartbeat_at, chats.created_at, chats.updated_at, chats.parent_chat_id, chats.root_chat_id, chats.last_model_config_id, chats.archived, chats.last_error, chats.mode, chats.mcp_server_ids, chats.labels, chats.build_id, chats.agent_id, chats.pin_order, chats.last_read_message_id, chats.last_injected_context,
     EXISTS (
         SELECT 1 FROM chat_messages cm
         WHERE cm.chat_id = chats.id
@@ -5426,6 +5429,7 @@ func (q *sqlQuerier) GetChats(ctx context.Context, arg GetChatsParams) ([]GetCha
 			&i.Chat.AgentID,
 			&i.Chat.PinOrder,
 			&i.Chat.LastReadMessageID,
+			&i.Chat.LastInjectedContext,
 			&i.HasUnread,
 		); err != nil {
 			return nil, err
@@ -5442,7 +5446,7 @@ func (q *sqlQuerier) GetChats(ctx context.Context, arg GetChatsParams) ([]GetCha
 }
 
 const getChatsByWorkspaceIDs = `-- name: GetChatsByWorkspaceIDs :many
-SELECT id, owner_id, workspace_id, title, status, worker_id, started_at, heartbeat_at, created_at, updated_at, parent_chat_id, root_chat_id, last_model_config_id, archived, last_error, mode, mcp_server_ids, labels, build_id, agent_id, pin_order, last_read_message_id
+SELECT id, owner_id, workspace_id, title, status, worker_id, started_at, heartbeat_at, created_at, updated_at, parent_chat_id, root_chat_id, last_model_config_id, archived, last_error, mode, mcp_server_ids, labels, build_id, agent_id, pin_order, last_read_message_id, last_injected_context
 FROM chats
 WHERE archived = false
   AND workspace_id = ANY($1::uuid[])
@@ -5481,6 +5485,7 @@ func (q *sqlQuerier) GetChatsByWorkspaceIDs(ctx context.Context, ids []uuid.UUID
 			&i.AgentID,
 			&i.PinOrder,
 			&i.LastReadMessageID,
+			&i.LastInjectedContext,
 		); err != nil {
 			return nil, err
 		}
@@ -5546,7 +5551,7 @@ func (q *sqlQuerier) GetLastChatMessageByRole(ctx context.Context, arg GetLastCh
 
 const getStaleChats = `-- name: GetStaleChats :many
 SELECT
-    id, owner_id, workspace_id, title, status, worker_id, started_at, heartbeat_at, created_at, updated_at, parent_chat_id, root_chat_id, last_model_config_id, archived, last_error, mode, mcp_server_ids, labels, build_id, agent_id, pin_order, last_read_message_id
+    id, owner_id, workspace_id, title, status, worker_id, started_at, heartbeat_at, created_at, updated_at, parent_chat_id, root_chat_id, last_model_config_id, archived, last_error, mode, mcp_server_ids, labels, build_id, agent_id, pin_order, last_read_message_id, last_injected_context
 FROM
     chats
 WHERE
@@ -5588,6 +5593,7 @@ func (q *sqlQuerier) GetStaleChats(ctx context.Context, staleThreshold time.Time
 			&i.AgentID,
 			&i.PinOrder,
 			&i.LastReadMessageID,
+			&i.LastInjectedContext,
 		); err != nil {
 			return nil, err
 		}
@@ -5669,7 +5675,7 @@ INSERT INTO chats (
     COALESCE($11::jsonb, '{}'::jsonb)
 )
 RETURNING
-    id, owner_id, workspace_id, title, status, worker_id, started_at, heartbeat_at, created_at, updated_at, parent_chat_id, root_chat_id, last_model_config_id, archived, last_error, mode, mcp_server_ids, labels, build_id, agent_id, pin_order, last_read_message_id
+    id, owner_id, workspace_id, title, status, worker_id, started_at, heartbeat_at, created_at, updated_at, parent_chat_id, root_chat_id, last_model_config_id, archived, last_error, mode, mcp_server_ids, labels, build_id, agent_id, pin_order, last_read_message_id, last_injected_context
 `
 
 type InsertChatParams struct {
@@ -5724,6 +5730,7 @@ func (q *sqlQuerier) InsertChat(ctx context.Context, arg InsertChatParams) (Chat
 		&i.AgentID,
 		&i.PinOrder,
 		&i.LastReadMessageID,
+		&i.LastInjectedContext,
 	)
 	return i, err
 }
@@ -6237,7 +6244,7 @@ UPDATE chats SET
     updated_at = NOW()
 WHERE
     id = $3::uuid
-RETURNING id, owner_id, workspace_id, title, status, worker_id, started_at, heartbeat_at, created_at, updated_at, parent_chat_id, root_chat_id, last_model_config_id, archived, last_error, mode, mcp_server_ids, labels, build_id, agent_id, pin_order, last_read_message_id
+RETURNING id, owner_id, workspace_id, title, status, worker_id, started_at, heartbeat_at, created_at, updated_at, parent_chat_id, root_chat_id, last_model_config_id, archived, last_error, mode, mcp_server_ids, labels, build_id, agent_id, pin_order, last_read_message_id, last_injected_context
 `
 
 type UpdateChatBuildAgentBindingParams struct {
@@ -6272,6 +6279,7 @@ func (q *sqlQuerier) UpdateChatBuildAgentBinding(ctx context.Context, arg Update
 		&i.AgentID,
 		&i.PinOrder,
 		&i.LastReadMessageID,
+		&i.LastInjectedContext,
 	)
 	return i, err
 }
@@ -6285,7 +6293,7 @@ SET
 WHERE
     id = $2::uuid
 RETURNING
-    id, owner_id, workspace_id, title, status, worker_id, started_at, heartbeat_at, created_at, updated_at, parent_chat_id, root_chat_id, last_model_config_id, archived, last_error, mode, mcp_server_ids, labels, build_id, agent_id, pin_order, last_read_message_id
+    id, owner_id, workspace_id, title, status, worker_id, started_at, heartbeat_at, created_at, updated_at, parent_chat_id, root_chat_id, last_model_config_id, archived, last_error, mode, mcp_server_ids, labels, build_id, agent_id, pin_order, last_read_message_id, last_injected_context
 `
 
 type UpdateChatByIDParams struct {
@@ -6319,6 +6327,7 @@ func (q *sqlQuerier) UpdateChatByID(ctx context.Context, arg UpdateChatByIDParam
 		&i.AgentID,
 		&i.PinOrder,
 		&i.LastReadMessageID,
+		&i.LastInjectedContext,
 	)
 	return i, err
 }
@@ -6358,7 +6367,7 @@ SET
 WHERE
     id = $2::uuid
 RETURNING
-    id, owner_id, workspace_id, title, status, worker_id, started_at, heartbeat_at, created_at, updated_at, parent_chat_id, root_chat_id, last_model_config_id, archived, last_error, mode, mcp_server_ids, labels, build_id, agent_id, pin_order, last_read_message_id
+    id, owner_id, workspace_id, title, status, worker_id, started_at, heartbeat_at, created_at, updated_at, parent_chat_id, root_chat_id, last_model_config_id, archived, last_error, mode, mcp_server_ids, labels, build_id, agent_id, pin_order, last_read_message_id, last_injected_context
 `
 
 type UpdateChatLabelsByIDParams struct {
@@ -6392,6 +6401,55 @@ func (q *sqlQuerier) UpdateChatLabelsByID(ctx context.Context, arg UpdateChatLab
 		&i.AgentID,
 		&i.PinOrder,
 		&i.LastReadMessageID,
+		&i.LastInjectedContext,
+	)
+	return i, err
+}
+
+const updateChatLastInjectedContext = `-- name: UpdateChatLastInjectedContext :one
+UPDATE chats SET
+    last_injected_context = $1::jsonb
+WHERE
+    id = $2::uuid
+RETURNING id, owner_id, workspace_id, title, status, worker_id, started_at, heartbeat_at, created_at, updated_at, parent_chat_id, root_chat_id, last_model_config_id, archived, last_error, mode, mcp_server_ids, labels, build_id, agent_id, pin_order, last_read_message_id, last_injected_context
+`
+
+type UpdateChatLastInjectedContextParams struct {
+	LastInjectedContext pqtype.NullRawMessage `db:"last_injected_context" json:"last_injected_context"`
+	ID                  uuid.UUID             `db:"id" json:"id"`
+}
+
+// Updates the cached injected context parts (AGENTS.md +
+// skills) on the chat row. Called only when context changes
+// (first workspace attach or agent change). updated_at is
+// intentionally not touched to avoid reordering the chat list.
+func (q *sqlQuerier) UpdateChatLastInjectedContext(ctx context.Context, arg UpdateChatLastInjectedContextParams) (Chat, error) {
+	row := q.db.QueryRowContext(ctx, updateChatLastInjectedContext, arg.LastInjectedContext, arg.ID)
+	var i Chat
+	err := row.Scan(
+		&i.ID,
+		&i.OwnerID,
+		&i.WorkspaceID,
+		&i.Title,
+		&i.Status,
+		&i.WorkerID,
+		&i.StartedAt,
+		&i.HeartbeatAt,
+		&i.CreatedAt,
+		&i.UpdatedAt,
+		&i.ParentChatID,
+		&i.RootChatID,
+		&i.LastModelConfigID,
+		&i.Archived,
+		&i.LastError,
+		&i.Mode,
+		pq.Array(&i.MCPServerIDs),
+		&i.Labels,
+		&i.BuildID,
+		&i.AgentID,
+		&i.PinOrder,
+		&i.LastReadMessageID,
+		&i.LastInjectedContext,
 	)
 	return i, err
 }
@@ -6405,7 +6463,7 @@ SET
 WHERE
     id = $2::uuid
 RETURNING
-    id, owner_id, workspace_id, title, status, worker_id, started_at, heartbeat_at, created_at, updated_at, parent_chat_id, root_chat_id, last_model_config_id, archived, last_error, mode, mcp_server_ids, labels, build_id, agent_id, pin_order, last_read_message_id
+    id, owner_id, workspace_id, title, status, worker_id, started_at, heartbeat_at, created_at, updated_at, parent_chat_id, root_chat_id, last_model_config_id, archived, last_error, mode, mcp_server_ids, labels, build_id, agent_id, pin_order, last_read_message_id, last_injected_context
 `
 
 type UpdateChatLastModelConfigByIDParams struct {
@@ -6439,6 +6497,7 @@ func (q *sqlQuerier) UpdateChatLastModelConfigByID(ctx context.Context, arg Upda
 		&i.AgentID,
 		&i.PinOrder,
 		&i.LastReadMessageID,
+		&i.LastInjectedContext,
 	)
 	return i, err
 }
@@ -6470,7 +6529,7 @@ SET
 WHERE
     id = $2::uuid
 RETURNING
-    id, owner_id, workspace_id, title, status, worker_id, started_at, heartbeat_at, created_at, updated_at, parent_chat_id, root_chat_id, last_model_config_id, archived, last_error, mode, mcp_server_ids, labels, build_id, agent_id, pin_order, last_read_message_id
+    id, owner_id, workspace_id, title, status, worker_id, started_at, heartbeat_at, created_at, updated_at, parent_chat_id, root_chat_id, last_model_config_id, archived, last_error, mode, mcp_server_ids, labels, build_id, agent_id, pin_order, last_read_message_id, last_injected_context
 `
 
 type UpdateChatMCPServerIDsParams struct {
@@ -6504,6 +6563,7 @@ func (q *sqlQuerier) UpdateChatMCPServerIDs(ctx context.Context, arg UpdateChatM
 		&i.AgentID,
 		&i.PinOrder,
 		&i.LastReadMessageID,
+		&i.LastInjectedContext,
 	)
 	return i, err
 }
@@ -6639,7 +6699,7 @@ SET
 WHERE
     id = $6::uuid
 RETURNING
-    id, owner_id, workspace_id, title, status, worker_id, started_at, heartbeat_at, created_at, updated_at, parent_chat_id, root_chat_id, last_model_config_id, archived, last_error, mode, mcp_server_ids, labels, build_id, agent_id, pin_order, last_read_message_id
+    id, owner_id, workspace_id, title, status, worker_id, started_at, heartbeat_at, created_at, updated_at, parent_chat_id, root_chat_id, last_model_config_id, archived, last_error, mode, mcp_server_ids, labels, build_id, agent_id, pin_order, last_read_message_id, last_injected_context
 `
 
 type UpdateChatStatusParams struct {
@@ -6684,6 +6744,7 @@ func (q *sqlQuerier) UpdateChatStatus(ctx context.Context, arg UpdateChatStatusP
 		&i.AgentID,
 		&i.PinOrder,
 		&i.LastReadMessageID,
+		&i.LastInjectedContext,
 	)
 	return i, err
 }
@@ -6701,7 +6762,7 @@ SET
 WHERE
     id = $7::uuid
 RETURNING
-    id, owner_id, workspace_id, title, status, worker_id, started_at, heartbeat_at, created_at, updated_at, parent_chat_id, root_chat_id, last_model_config_id, archived, last_error, mode, mcp_server_ids, labels, build_id, agent_id, pin_order, last_read_message_id
+    id, owner_id, workspace_id, title, status, worker_id, started_at, heartbeat_at, created_at, updated_at, parent_chat_id, root_chat_id, last_model_config_id, archived, last_error, mode, mcp_server_ids, labels, build_id, agent_id, pin_order, last_read_message_id, last_injected_context
 `
 
 type UpdateChatStatusPreserveUpdatedAtParams struct {
@@ -6748,6 +6809,7 @@ func (q *sqlQuerier) UpdateChatStatusPreserveUpdatedAt(ctx context.Context, arg
 		&i.AgentID,
 		&i.PinOrder,
 		&i.LastReadMessageID,
+		&i.LastInjectedContext,
 	)
 	return i, err
 }
@@ -6759,7 +6821,7 @@ UPDATE chats SET
     agent_id = $3::uuid,
     updated_at = NOW()
 WHERE id = $4::uuid
-RETURNING id, owner_id, workspace_id, title, status, worker_id, started_at, heartbeat_at, created_at, updated_at, parent_chat_id, root_chat_id, last_model_config_id, archived, last_error, mode, mcp_server_ids, labels, build_id, agent_id, pin_order, last_read_message_id
+RETURNING id, owner_id, workspace_id, title, status, worker_id, started_at, heartbeat_at, created_at, updated_at, parent_chat_id, root_chat_id, last_model_config_id, archived, last_error, mode, mcp_server_ids, labels, build_id, agent_id, pin_order, last_read_message_id, last_injected_context
 `
 
 type UpdateChatWorkspaceBindingParams struct {
@@ -6800,6 +6862,7 @@ func (q *sqlQuerier) UpdateChatWorkspaceBinding(ctx context.Context, arg UpdateC
 		&i.AgentID,
 		&i.PinOrder,
 		&i.LastReadMessageID,
+		&i.LastInjectedContext,
 	)
 	return i, err
 }

coderd/database/queries/chats.sql

@@ -528,6 +528,17 @@ WHERE
     id = @id::uuid
 RETURNING *;
 
+-- name: UpdateChatLastInjectedContext :one
+-- Updates the cached injected context parts (AGENTS.md +
+-- skills) on the chat row. Called only when context changes
+-- (first workspace attach or agent change). updated_at is
+-- intentionally not touched to avoid reordering the chat list.
+UPDATE chats SET
+    last_injected_context = sqlc.narg('last_injected_context')::jsonb
+WHERE
+    id = @id::uuid
+RETURNING *;
+
 -- name: UpdateChatMCPServerIDs :one
 UPDATE
     chats

coderd/x/chatd/chatd.go

@@ -4970,9 +4970,25 @@ func (p *Server) persistInstructionFiles(
 			chatprompt.CurrentContentVersion,
 		))
 		_, _ = p.db.InsertChatMessages(ctx, msgParams)
+		// Update the cache column: persist skills if any
+		// exist, or clear to NULL so stale data from a
+		// previous agent doesn't linger.
+		if len(discoveredSkills) > 0 {
+			skillParts := make([]codersdk.ChatMessagePart, 0, len(discoveredSkills))
+			for _, s := range discoveredSkills {
+				skillParts = append(skillParts, codersdk.ChatMessagePart{
+					Type:               codersdk.ChatMessagePartTypeSkill,
+					SkillName:          s.Name,
+					SkillDescription:   s.Description,
+					ContextFileAgentID: uuid.NullUUID{UUID: agent.ID, Valid: true},
+				})
+			}
+			p.updateLastInjectedContext(ctx, chat.ID, skillParts)
+		} else {
+			p.updateLastInjectedContext(ctx, chat.ID, nil)
+		}
 		return "", discoveredSkills, nil
 	}
-
 	// Build context-file parts (one per instruction file) and
 	// skill parts (one per discovered skill).
 	parts := make([]codersdk.ChatMessagePart, 0, len(sections)+len(discoveredSkills))
@@ -5015,6 +5031,15 @@ func (p *Server) persistInstructionFiles(
 	if _, err := p.db.InsertChatMessages(ctx, msgParams); err != nil {
 		return "", nil, xerrors.Errorf("persist instruction files: %w", err)
 	}
+	// Build stripped copies for the cache column so internal
+	// fields (full file content, OS, directory, skill paths)
+	// are never persisted or returned to API clients.
+	stripped := make([]codersdk.ChatMessagePart, len(parts))
+	copy(stripped, parts)
+	for i := range stripped {
+		stripped[i].StripInternal()
+	}
+	p.updateLastInjectedContext(ctx, chat.ID, stripped)
 
 	// Return the formatted instruction text and discovered skills
 	// so the caller can inject them into this turn's prompt (since
@@ -5022,6 +5047,35 @@ func (p *Server) persistInstructionFiles(
 	return formatSystemInstructions(agent.OperatingSystem, directory, sections), discoveredSkills, nil
 }
 
+// updateLastInjectedContext persists the injected context
+// parts (AGENTS.md files and skills) on the chat row so they
+// are directly queryable without scanning messages. This is
+// best-effort — a failure here is logged but does not block
+// the turn.
+func (p *Server) updateLastInjectedContext(ctx context.Context, chatID uuid.UUID, parts []codersdk.ChatMessagePart) {
+	param := pqtype.NullRawMessage{Valid: false}
+	if parts != nil {
+		raw, err := json.Marshal(parts)
+		if err != nil {
+			p.logger.Warn(ctx, "failed to marshal injected context",
+				slog.F("chat_id", chatID),
+				slog.Error(err),
+			)
+			return
+		}
+		param = pqtype.NullRawMessage{RawMessage: raw, Valid: true}
+	}
+	if _, err := p.db.UpdateChatLastInjectedContext(ctx, database.UpdateChatLastInjectedContextParams{
+		ID:                  chatID,
+		LastInjectedContext: param,
+	}); err != nil {
+		p.logger.Warn(ctx, "failed to update injected context",
+			slog.F("chat_id", chatID),
+			slog.Error(err),
+		)
+	}
+}
+
 // resolveUserCompactionThreshold looks up the user's per-model
 // compaction threshold override. Returns the override value and
 // true if one exists and is valid, or 0 and false otherwise.

coderd/x/chatd/chatd_internal_test.go

@@ -484,6 +484,32 @@ func TestPersistInstructionFilesIncludesAgentMetadata(t *testing.T) {
 		agentID,
 	).Return(workspaceAgent, nil).Times(1)
 	db.EXPECT().InsertChatMessages(gomock.Any(), gomock.Any()).Return(nil, nil).AnyTimes()
+	db.EXPECT().UpdateChatLastInjectedContext(gomock.Any(),
+		gomock.Cond(func(x any) bool {
+			arg, ok := x.(database.UpdateChatLastInjectedContextParams)
+			if !ok || arg.ID != chat.ID {
+				return false
+			}
+			if !arg.LastInjectedContext.Valid {
+				return false
+			}
+			var parts []codersdk.ChatMessagePart
+			if err := json.Unmarshal(arg.LastInjectedContext.RawMessage, &parts); err != nil {
+				return false
+			}
+			// Expect at least one context-file part for the
+			// working-directory AGENTS.md, with internal fields
+			// stripped (no content, OS, or directory).
+			for _, p := range parts {
+				if p.Type == codersdk.ChatMessagePartTypeContextFile && p.ContextFilePath != "" {
+					return p.ContextFileContent == "" &&
+						p.ContextFileOS == "" &&
+						p.ContextFileDirectory == ""
+				}
+			}
+			return false
+		}),
+	).Return(database.Chat{}, nil).Times(1)
 
 	conn := agentconnmock.NewMockAgentConn(ctrl)
 	conn.EXPECT().SetExtraHeaders(gomock.Any()).Times(1)
@@ -569,6 +595,247 @@ func TestPersistInstructionFilesSkipsSentinelWhenWorkspaceUnavailable(t *testing
 	require.Empty(t, instruction)
 }
 
+func TestPersistInstructionFilesSentinelWithSkills(t *testing.T) {
+	t.Parallel()
+
+	ctx := context.Background()
+	ctrl := gomock.NewController(t)
+	db := dbmock.NewMockStore(ctrl)
+
+	workspaceID := uuid.New()
+	agentID := uuid.New()
+	chat := database.Chat{
+		ID: uuid.New(),
+		WorkspaceID: uuid.NullUUID{
+			UUID:  workspaceID,
+			Valid: true,
+		},
+		AgentID: uuid.NullUUID{
+			UUID:  agentID,
+			Valid: true,
+		},
+	}
+	workspaceAgent := database.WorkspaceAgent{
+		ID:                agentID,
+		OperatingSystem:   "linux",
+		Directory:         "/home/coder/project",
+		ExpandedDirectory: "/home/coder/project",
+	}
+
+	db.EXPECT().GetWorkspaceAgentByID(
+		gomock.Any(),
+		agentID,
+	).Return(workspaceAgent, nil).Times(1)
+	db.EXPECT().InsertChatMessages(gomock.Any(), gomock.Any()).Return(nil, nil).AnyTimes()
+	db.EXPECT().UpdateChatLastInjectedContext(gomock.Any(),
+		gomock.Cond(func(x any) bool {
+			arg, ok := x.(database.UpdateChatLastInjectedContextParams)
+			if !ok || arg.ID != chat.ID {
+				return false
+			}
+			if !arg.LastInjectedContext.Valid {
+				return false
+			}
+			var parts []codersdk.ChatMessagePart
+			if err := json.Unmarshal(arg.LastInjectedContext.RawMessage, &parts); err != nil {
+				return false
+			}
+			// The sentinel path should persist only skill parts
+			// with ContextFileAgentID set.
+			for _, p := range parts {
+				if p.Type == codersdk.ChatMessagePartTypeSkill &&
+					p.SkillName == "my-skill" &&
+					p.ContextFileAgentID == (uuid.NullUUID{UUID: agentID, Valid: true}) {
+					return true
+				}
+			}
+			return false
+		}),
+	).Return(database.Chat{}, nil).Times(1)
+
+	conn := agentconnmock.NewMockAgentConn(ctrl)
+	conn.EXPECT().SetExtraHeaders(gomock.Any()).Times(1)
+
+	// Home LS (.coder directory): return 404 so no home
+	// instruction file is found.
+	conn.EXPECT().LS(gomock.Any(), "",
+		gomock.Cond(func(x any) bool {
+			req, ok := x.(workspacesdk.LSRequest)
+			return ok && req.Relativity == workspacesdk.LSRelativityHome
+		}),
+	).Return(
+		workspacesdk.LSResponse{},
+		codersdk.NewTestError(404, "POST", "/api/v0/list-directory"),
+	).Times(1)
+
+	// Pwd AGENTS.md: return 404 so no working-directory
+	// instruction file is found either.
+	conn.EXPECT().ReadFile(gomock.Any(),
+		"/home/coder/project/AGENTS.md",
+		int64(0),
+		int64(maxInstructionFileBytes+1),
+	).Return(
+		nil, "",
+		codersdk.NewTestError(404, "GET", "/api/v0/read-file"),
+	).Times(1)
+
+	// Skills LS (.agents/skills directory): return one skill
+	// directory so DiscoverSkills finds it.
+	conn.EXPECT().LS(gomock.Any(), "",
+		gomock.Cond(func(x any) bool {
+			req, ok := x.(workspacesdk.LSRequest)
+			return ok && req.Relativity == workspacesdk.LSRelativityRoot
+		}),
+	).Return(workspacesdk.LSResponse{
+		Contents: []workspacesdk.LSFile{{
+			Name:               "my-skill",
+			AbsolutePathString: "/home/coder/project/.agents/skills/my-skill",
+			IsDir:              true,
+		}},
+	}, nil).Times(1)
+
+	// Skills SKILL.md ReadFile: return valid frontmatter.
+	skillContent := "---\nname: my-skill\ndescription: A test skill\n---\nSkill body"
+	conn.EXPECT().ReadFile(gomock.Any(),
+		"/home/coder/project/.agents/skills/my-skill/SKILL.md",
+		int64(0),
+		int64(64*1024+1),
+	).Return(
+		io.NopCloser(strings.NewReader(skillContent)),
+		"",
+		nil,
+	).Times(1)
+
+	logger := slogtest.Make(t, &slogtest.Options{IgnoreErrors: true})
+	server := &Server{
+		db:     db,
+		logger: logger,
+		agentConnFn: func(context.Context, uuid.UUID) (workspacesdk.AgentConn, func(), error) {
+			return conn, func() {}, nil
+		},
+	}
+
+	chatStateMu := &sync.Mutex{}
+	currentChat := chat
+	workspaceCtx := turnWorkspaceContext{
+		server:           server,
+		chatStateMu:      chatStateMu,
+		currentChat:      &currentChat,
+		loadChatSnapshot: func(context.Context, uuid.UUID) (database.Chat, error) { return database.Chat{}, nil },
+	}
+	t.Cleanup(workspaceCtx.close)
+
+	instruction, skills, err := server.persistInstructionFiles(
+		ctx,
+		chat,
+		uuid.New(),
+		workspaceCtx.getWorkspaceAgent,
+		workspaceCtx.getWorkspaceConn,
+	)
+	require.NoError(t, err)
+	// Sentinel path returns empty instruction string.
+	require.Empty(t, instruction)
+	// Skills are still discovered and returned.
+	require.Len(t, skills, 1)
+	require.Equal(t, "my-skill", skills[0].Name)
+}
+
+func TestPersistInstructionFilesSentinelNoSkillsClearsColumn(t *testing.T) {
+	t.Parallel()
+
+	ctx := context.Background()
+	ctrl := gomock.NewController(t)
+	db := dbmock.NewMockStore(ctrl)
+
+	workspaceID := uuid.New()
+	agentID := uuid.New()
+	chat := database.Chat{
+		ID: uuid.New(),
+		WorkspaceID: uuid.NullUUID{
+			UUID:  workspaceID,
+			Valid: true,
+		},
+		AgentID: uuid.NullUUID{
+			UUID:  agentID,
+			Valid: true,
+		},
+	}
+	workspaceAgent := database.WorkspaceAgent{
+		ID:                agentID,
+		OperatingSystem:   "linux",
+		Directory:         "/home/coder/project",
+		ExpandedDirectory: "/home/coder/project",
+	}
+
+	db.EXPECT().GetWorkspaceAgentByID(
+		gomock.Any(),
+		agentID,
+	).Return(workspaceAgent, nil).Times(1)
+	db.EXPECT().InsertChatMessages(gomock.Any(), gomock.Any()).Return(nil, nil).AnyTimes()
+	db.EXPECT().UpdateChatLastInjectedContext(gomock.Any(),
+		gomock.Cond(func(x any) bool {
+			arg, ok := x.(database.UpdateChatLastInjectedContextParams)
+			if !ok || arg.ID != chat.ID {
+				return false
+			}
+			// No skills discovered, so the column should be
+			// cleared to NULL.
+			return !arg.LastInjectedContext.Valid
+		}),
+	).Return(database.Chat{}, nil).Times(1)
+
+	conn := agentconnmock.NewMockAgentConn(ctrl)
+	conn.EXPECT().SetExtraHeaders(gomock.Any()).Times(1)
+
+	// All LS calls return 404: no home .coder directory and no
+	// .agents/skills directory.
+	conn.EXPECT().LS(gomock.Any(), "", gomock.Any()).Return(
+		workspacesdk.LSResponse{},
+		codersdk.NewTestError(404, "POST", "/api/v0/list-directory"),
+	).AnyTimes()
+
+	// Pwd AGENTS.md: return 404.
+	conn.EXPECT().ReadFile(gomock.Any(),
+		"/home/coder/project/AGENTS.md",
+		int64(0),
+		int64(maxInstructionFileBytes+1),
+	).Return(
+		nil, "",
+		codersdk.NewTestError(404, "GET", "/api/v0/read-file"),
+	).Times(1)
+
+	logger := slogtest.Make(t, &slogtest.Options{IgnoreErrors: true})
+	server := &Server{
+		db:     db,
+		logger: logger,
+		agentConnFn: func(context.Context, uuid.UUID) (workspacesdk.AgentConn, func(), error) {
+			return conn, func() {}, nil
+		},
+	}
+
+	chatStateMu := &sync.Mutex{}
+	currentChat := chat
+	workspaceCtx := turnWorkspaceContext{
+		server:           server,
+		chatStateMu:      chatStateMu,
+		currentChat:      &currentChat,
+		loadChatSnapshot: func(context.Context, uuid.UUID) (database.Chat, error) { return database.Chat{}, nil },
+	}
+	t.Cleanup(workspaceCtx.close)
+
+	instruction, skills, err := server.persistInstructionFiles(
+		ctx,
+		chat,
+		uuid.New(),
+		workspaceCtx.getWorkspaceAgent,
+		workspaceCtx.getWorkspaceConn,
+	)
+	require.NoError(t, err)
+	// Sentinel path: empty instruction, no skills.
+	require.Empty(t, instruction)
+	require.Empty(t, skills)
+}
+
 func TestTurnWorkspaceContext_BindingFirstPath(t *testing.T) {
 	t.Parallel()