fix: update directory for terraform-managed subagents (#24220)

When a devcontainer subagent is terraform-managed, the provisioner sets
its directory to the host-side `workspace_folder` path at build time. At
runtime, the agent injection code determines the correct
container-internal
path from `devcontainer read-configuration` and sends it via
`CreateSubAgent`.

However, the `CreateSubAgent` handler only updated `display_apps` for
pre-existing agents, ignoring the `Directory` field. This caused
SSH/terminal
sessions to land in `~` instead of the workspace folder (e.g.
`/workspaces/foo`).

Add `UpdateWorkspaceAgentDirectoryByID` query and call it in the
terraform-managed subagent update path to also persist the directory.

Fixes PLAT-118

<details><summary>Root cause analysis</summary>

Two code paths set the subagent `Directory` field:

1. **Provisioner (build time):** `insertDevcontainerSubagent` in
`provisionerdserver.go`
   stores `dc.GetWorkspaceFolder()` — the **host-side** path from the
   `coder_devcontainer` Terraform resource (e.g. `/home/coder/project`).

2. **Agent injection (runtime):**
`maybeInjectSubAgentIntoContainerLocked` in
`api.go` reads the devcontainer config and gets the correct
**container-internal**
path (e.g. `/workspaces/project`), then calls `client.Create(ctx,
subAgentConfig)`.

For terraform-managed subagents (those with `req.Id != nil`),
`CreateSubAgent`
in `coderd/agentapi/subagent.go` recognized the pre-existing agent and
entered
the update path — but only called `UpdateWorkspaceAgentDisplayAppsByID`,
discarding the `Directory` field from the request. The agent kept the
stale
host-side path, which doesn't exist inside the container, causing
`expandPathToAbs` to fall back to `~`.

</details>

> [!NOTE]
> Generated by Coder Agents

coderd/database/dbauthz/dbauthz.go

@@ -6783,6 +6783,19 @@ func (q *querier) UpdateWorkspaceAgentConnectionByID(ctx context.Context, arg da
 	return q.db.UpdateWorkspaceAgentConnectionByID(ctx, arg)
 }
 
+func (q *querier) UpdateWorkspaceAgentDirectoryByID(ctx context.Context, arg database.UpdateWorkspaceAgentDirectoryByIDParams) error {
+	workspace, err := q.db.GetWorkspaceByAgentID(ctx, arg.ID)
+	if err != nil {
+		return err
+	}
+
+	if err := q.authorizeContext(ctx, policy.ActionUpdateAgent, workspace); err != nil {
+		return err
+	}
+
+	return q.db.UpdateWorkspaceAgentDirectoryByID(ctx, arg)
+}
+
 func (q *querier) UpdateWorkspaceAgentDisplayAppsByID(ctx context.Context, arg database.UpdateWorkspaceAgentDisplayAppsByIDParams) error {
 	workspace, err := q.db.GetWorkspaceByAgentID(ctx, arg.ID)
 	if err != nil {

coderd/database/dbauthz/dbauthz_test.go

@@ -2935,6 +2935,17 @@ func (s *MethodTestSuite) TestWorkspace() {
 		dbm.EXPECT().UpdateWorkspaceAgentStartupByID(gomock.Any(), arg).Return(nil).AnyTimes()
 		check.Args(arg).Asserts(w, policy.ActionUpdate).Returns()
 	}))
+	s.Run("UpdateWorkspaceAgentDirectoryByID", s.Mocked(func(dbm *dbmock.MockStore, faker *gofakeit.Faker, check *expects) {
+		w := testutil.Fake(s.T(), faker, database.Workspace{})
+		agt := testutil.Fake(s.T(), faker, database.WorkspaceAgent{})
+		arg := database.UpdateWorkspaceAgentDirectoryByIDParams{
+			ID:        agt.ID,
+			Directory: "/workspaces/project",
+		}
+		dbm.EXPECT().GetWorkspaceByAgentID(gomock.Any(), agt.ID).Return(w, nil).AnyTimes()
+		dbm.EXPECT().UpdateWorkspaceAgentDirectoryByID(gomock.Any(), arg).Return(nil).AnyTimes()
+		check.Args(arg).Asserts(w, policy.ActionUpdateAgent).Returns()
+	}))
 	s.Run("UpdateWorkspaceAgentDisplayAppsByID", s.Mocked(func(dbm *dbmock.MockStore, faker *gofakeit.Faker, check *expects) {
 		w := testutil.Fake(s.T(), faker, database.Workspace{})
 		agt := testutil.Fake(s.T(), faker, database.WorkspaceAgent{})

coderd/database/dbmetrics/querymetrics.go

@@ -4840,6 +4840,14 @@ func (m queryMetricsStore) UpdateWorkspaceAgentConnectionByID(ctx context.Contex
 	return r0
 }
 
+func (m queryMetricsStore) UpdateWorkspaceAgentDirectoryByID(ctx context.Context, arg database.UpdateWorkspaceAgentDirectoryByIDParams) error {
+	start := time.Now()
+	r0 := m.s.UpdateWorkspaceAgentDirectoryByID(ctx, arg)
+	m.queryLatencies.WithLabelValues("UpdateWorkspaceAgentDirectoryByID").Observe(time.Since(start).Seconds())
+	m.queryCounts.WithLabelValues(httpmw.ExtractHTTPRoute(ctx), httpmw.ExtractHTTPMethod(ctx), "UpdateWorkspaceAgentDirectoryByID").Inc()
+	return r0
+}
+
 func (m queryMetricsStore) UpdateWorkspaceAgentDisplayAppsByID(ctx context.Context, arg database.UpdateWorkspaceAgentDisplayAppsByIDParams) error {
 	start := time.Now()
 	r0 := m.s.UpdateWorkspaceAgentDisplayAppsByID(ctx, arg)

coderd/database/dbmock/dbmock.go

@@ -9120,6 +9120,20 @@ func (mr *MockStoreMockRecorder) UpdateWorkspaceAgentConnectionByID(ctx, arg any
 	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "UpdateWorkspaceAgentConnectionByID", reflect.TypeOf((*MockStore)(nil).UpdateWorkspaceAgentConnectionByID), ctx, arg)
 }
 
+// UpdateWorkspaceAgentDirectoryByID mocks base method.
+func (m *MockStore) UpdateWorkspaceAgentDirectoryByID(ctx context.Context, arg database.UpdateWorkspaceAgentDirectoryByIDParams) error {
+	m.ctrl.T.Helper()
+	ret := m.ctrl.Call(m, "UpdateWorkspaceAgentDirectoryByID", ctx, arg)
+	ret0, _ := ret[0].(error)
+	return ret0
+}
+
+// UpdateWorkspaceAgentDirectoryByID indicates an expected call of UpdateWorkspaceAgentDirectoryByID.
+func (mr *MockStoreMockRecorder) UpdateWorkspaceAgentDirectoryByID(ctx, arg any) *gomock.Call {
+	mr.mock.ctrl.T.Helper()
+	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "UpdateWorkspaceAgentDirectoryByID", reflect.TypeOf((*MockStore)(nil).UpdateWorkspaceAgentDirectoryByID), ctx, arg)
+}
+
 // UpdateWorkspaceAgentDisplayAppsByID mocks base method.
 func (m *MockStore) UpdateWorkspaceAgentDisplayAppsByID(ctx context.Context, arg database.UpdateWorkspaceAgentDisplayAppsByIDParams) error {
 	m.ctrl.T.Helper()

coderd/database/querier.go

@@ -1011,6 +1011,7 @@ type sqlcQuerier interface {
 	UpdateWorkspace(ctx context.Context, arg UpdateWorkspaceParams) (WorkspaceTable, error)
 	UpdateWorkspaceACLByID(ctx context.Context, arg UpdateWorkspaceACLByIDParams) error
 	UpdateWorkspaceAgentConnectionByID(ctx context.Context, arg UpdateWorkspaceAgentConnectionByIDParams) error
+	UpdateWorkspaceAgentDirectoryByID(ctx context.Context, arg UpdateWorkspaceAgentDirectoryByIDParams) error
 	UpdateWorkspaceAgentDisplayAppsByID(ctx context.Context, arg UpdateWorkspaceAgentDisplayAppsByIDParams) error
 	UpdateWorkspaceAgentLifecycleStateByID(ctx context.Context, arg UpdateWorkspaceAgentLifecycleStateByIDParams) error
 	UpdateWorkspaceAgentLogOverflowByID(ctx context.Context, arg UpdateWorkspaceAgentLogOverflowByIDParams) error

coderd/database/queries.sql.go

@@ -26816,6 +26816,26 @@ func (q *sqlQuerier) UpdateWorkspaceAgentConnectionByID(ctx context.Context, arg
 	return err
 }
 
+const updateWorkspaceAgentDirectoryByID = `-- name: UpdateWorkspaceAgentDirectoryByID :exec
+UPDATE
+	workspace_agents
+SET
+	directory = $2, updated_at = $3
+WHERE
+	id = $1
+`
+
+type UpdateWorkspaceAgentDirectoryByIDParams struct {
+	ID        uuid.UUID `db:"id" json:"id"`
+	Directory string    `db:"directory" json:"directory"`
+	UpdatedAt time.Time `db:"updated_at" json:"updated_at"`
+}
+
+func (q *sqlQuerier) UpdateWorkspaceAgentDirectoryByID(ctx context.Context, arg UpdateWorkspaceAgentDirectoryByIDParams) error {
+	_, err := q.db.ExecContext(ctx, updateWorkspaceAgentDirectoryByID, arg.ID, arg.Directory, arg.UpdatedAt)
+	return err
+}
+
 const updateWorkspaceAgentDisplayAppsByID = `-- name: UpdateWorkspaceAgentDisplayAppsByID :exec
 UPDATE
 	workspace_agents

coderd/database/queries/workspaceagents.sql

@@ -190,6 +190,14 @@ SET
 WHERE
 	id = $1;
 
+-- name: UpdateWorkspaceAgentDirectoryByID :exec
+UPDATE
+	workspace_agents
+SET
+	directory = $2, updated_at = $3
+WHERE
+	id = $1;
+
 -- name: GetWorkspaceAgentLogsAfter :many
 SELECT
 	*