fix(update): detach in-place update from the HTTP request lifetime

The in-place update ran entirely inside c.Request.Context(). Browsers and
reverse proxies commonly abort long-idle requests (axios global timeout
30s, nginx proxy_read_timeout 60s by default), which canceled the request
context mid-download and killed every slow update with
'download failed: context canceled' while the version stayed unchanged.
Users behind slow GitHub links saw the update button fail at a wall-clock
ceiling (~60s) on every attempt (#4504).

- Run PerformUpdate and RollbackToVersion on a context detached from the
  request (context.WithoutCancel) and bounded by a 15-minute deadline so
  the 10-minute GitHub download client owns its own timeout. A client
  disconnect no longer aborts the binary swap; retries then hit the
  system operation lock or report 'Already up to date'.
- Raise the frontend timeout for the update/rollback calls from the
  global 30s axios default to 15 minutes so the browser can actually
  wait for the result.

Fixes #4504

backend/internal/handler/admin/system_handler_test.go

@@ -18,18 +18,22 @@ import (
 )
 
 type systemHandlerUpdateServiceStub struct {
-	performErr           error
-	updateInfo           *service.UpdateInfo
-	checkErr             error
-	checkForces          []bool
-	performCall          int
-	rollbackCall         int
-	rollbackToCall       int
-	rollbackToVersions   []string
-	rollbackToErr        error
-	rollbackVersions     []service.RollbackVersion
-	rollbackVersionsErr  error
-	rollbackVersionsCall int
+	performErr            error
+	updateInfo            *service.UpdateInfo
+	checkErr              error
+	checkForces           []bool
+	performCall           int
+	performCtxErr         error
+	performHasDeadline    bool
+	rollbackCall          int
+	rollbackToCall        int
+	rollbackToCtxErr      error
+	rollbackToHasDeadline bool
+	rollbackToVersions    []string
+	rollbackToErr         error
+	rollbackVersions      []service.RollbackVersion
+	rollbackVersionsErr   error
+	rollbackVersionsCall  int
 }
 
 func (s *systemHandlerUpdateServiceStub) CheckUpdate(_ context.Context, force bool) (*service.UpdateInfo, error) {
@@ -37,8 +41,10 @@ func (s *systemHandlerUpdateServiceStub) CheckUpdate(_ context.Context, force bo
 	return s.updateInfo, s.checkErr
 }
 
-func (s *systemHandlerUpdateServiceStub) PerformUpdate(context.Context) error {
+func (s *systemHandlerUpdateServiceStub) PerformUpdate(ctx context.Context) error {
 	s.performCall++
+	s.performCtxErr = ctx.Err()
+	_, s.performHasDeadline = ctx.Deadline()
 	return s.performErr
 }
 
@@ -52,8 +58,10 @@ func (s *systemHandlerUpdateServiceStub) ListRollbackVersions(context.Context) (
 	return s.rollbackVersions, s.rollbackVersionsErr
 }
 
-func (s *systemHandlerUpdateServiceStub) RollbackToVersion(_ context.Context, version string) error {
+func (s *systemHandlerUpdateServiceStub) RollbackToVersion(ctx context.Context, version string) error {
 	s.rollbackToCall++
+	s.rollbackToCtxErr = ctx.Err()
+	_, s.rollbackToHasDeadline = ctx.Deadline()
 	s.rollbackToVersions = append(s.rollbackToVersions, version)
 	return s.rollbackToErr
 }
@@ -165,6 +173,55 @@ func TestSystemHandlerPerformUpdateFailureStillReturnsInternalError(t *testing.T
 	require.Equal(t, "internal error", body.Message)
 }
 
+// TestSystemHandlerPerformUpdateSurvivesClientDisconnect reproduces #4504:
+// the browser or a reverse proxy (axios 30s default, nginx proxy_read_timeout
+// 60s) aborts the long-running update request and cancels the request
+// context. The download must keep running on a detached, bounded context
+// instead of dying with "download failed: context canceled".
+func TestSystemHandlerPerformUpdateSurvivesClientDisconnect(t *testing.T) {
+	updateSvc := &systemHandlerUpdateServiceStub{}
+	repo := newMemoryIdempotencyRepoStub()
+	router := newSystemHandlerTestRouter(t, updateSvc, repo)
+
+	rec := httptest.NewRecorder()
+	req := httptest.NewRequest(http.MethodPost, "/api/v1/admin/system/update", nil)
+	canceledCtx, cancel := context.WithCancel(context.Background())
+	cancel()
+	req = req.WithContext(canceledCtx)
+	req.Header.Set("Idempotency-Key", "disconnected-update")
+	router.ServeHTTP(rec, req)
+
+	require.Equal(t, 1, updateSvc.performCall)
+	require.NoError(t, updateSvc.performCtxErr,
+		"update must not observe the canceled request context")
+	require.True(t, updateSvc.performHasDeadline,
+		"detached update context must still be bounded by a deadline")
+	requireSystemLockStatus(t, repo, service.IdempotencyStatusSucceeded)
+}
+
+func TestSystemHandlerRollbackToVersionSurvivesClientDisconnect(t *testing.T) {
+	updateSvc := &systemHandlerUpdateServiceStub{}
+	repo := newMemoryIdempotencyRepoStub()
+	router := newSystemHandlerTestRouter(t, updateSvc, repo)
+
+	rec := httptest.NewRecorder()
+	req := httptest.NewRequest(http.MethodPost, "/api/v1/admin/system/rollback",
+		strings.NewReader(`{"version":"0.1.146"}`))
+	req.Header.Set("Content-Type", "application/json")
+	canceledCtx, cancel := context.WithCancel(context.Background())
+	cancel()
+	req = req.WithContext(canceledCtx)
+	req.Header.Set("Idempotency-Key", "disconnected-rollback")
+	router.ServeHTTP(rec, req)
+
+	require.Equal(t, 1, updateSvc.rollbackToCall)
+	require.NoError(t, updateSvc.rollbackToCtxErr,
+		"versioned rollback must not observe the canceled request context")
+	require.True(t, updateSvc.rollbackToHasDeadline,
+		"detached rollback context must still be bounded by a deadline")
+	requireSystemLockStatus(t, repo, service.IdempotencyStatusSucceeded)
+}
+
 func TestSystemHandlerRollbackWithoutBodyUsesLegacyBackup(t *testing.T) {
 	updateSvc := &systemHandlerUpdateServiceStub{}
 	repo := newMemoryIdempotencyRepoStub()