Rework Tasks tab: Chains section, checklist modal, project visibility

The flat Tasks-tab atom list was silently dumping every chain step
(locked and unlocked) and dormant bucket-pool items in as ordinary
undated cards, with no chain/project context and no protection against
completing a locked step out of order.

- CompleteNativeTask now rejects completing a locked chain task
  (ErrChainTaskLocked), mapped to 400 in both the widget and web
  complete-atom handlers.
- Chain tasks and dormant bucket items are excluded from the flat atom
  list; a new "Chains" section shows one card per active/paused chain
  with the current step and N/M progress.
- New chain checklist modal (GET /chains/{id}) lists every position in
  order with pause/resume/abandon -- the web view originally deferred
  as Android-only.
- Fixed a real bug this surfaced: resuming a paused chain only flipped
  the status flag, never unlocking the deferred successor, so a chain
  paused right after a completion stayed stuck forever. SetChainStatus
  now catches up the deferred advancement on resume, idempotently.
- Atom cards gained a project-name chip for general visibility.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EZ7ikw2ukGJFTHE3bJS7zL

1 files changed, 67 insertions, 1 deletions

diff --git a/internal/store/chains_test.go b/internal/store/chains_test.go
index 1d16508..6359d11 100644
--- a/internal/store/chains_test.go
+++ b/internal/store/chains_test.go
@@ -132,10 +132,19 @@ func TestCompleteNativeTask_PausedChain_DoesNotAdvance(t *testing.T) {
 		t.Error("position 1 should still be locked while chain is paused")
 	}
 
-	// Resuming re-enables advancement on the *next* completion.
+	// Resuming performs the deferred unlock itself -- position 1 becomes
+	// completable immediately, not only after some future completion.
 	if err := s.SetChainStatus(chain.ID, "active"); err != nil {
 		t.Fatal(err)
 	}
+	resumed, err := s.GetChainTasks(chain.ID)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !resumed[1].ChainUnlocked {
+		t.Fatal("expected resume to unlock position 1 immediately (deferred advancement catch-up)")
+	}
+
 	if err := s.CompleteNativeTask(tasks[1].ID); err != nil {
 		t.Fatalf("CompleteNativeTask after resume: %v", err)
 	}
@@ -148,6 +157,63 @@ func TestCompleteNativeTask_PausedChain_DoesNotAdvance(t *testing.T) {
 	}
 }
 
+func TestCompleteNativeTask_LockedChainTask_ReturnsErrChainTaskLocked(t *testing.T) {
+	s := newNativeTasksTestStore(t)
+
+	chain, err := s.CreateChain("Track", chainTasks("Step 1", "Step 2"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	tasks, err := s.GetChainTasks(chain.ID)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if err := s.CompleteNativeTask(tasks[1].ID); err != ErrChainTaskLocked {
+		t.Errorf("err = %v, want ErrChainTaskLocked", err)
+	}
+
+	// Confirm nothing was mutated -- still locked, still not completed.
+	after, err := s.GetChainTasks(chain.ID)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if after[1].Completed || after[1].ChainUnlocked {
+		t.Errorf("locked task should be untouched by the rejected completion attempt: %+v", after[1])
+	}
+}
+
+func TestSetChainStatus_ResumeWithNothingStuck_DoesNotResetDueDate(t *testing.T) {
+	s := newNativeTasksTestStore(t)
+
+	chain, err := s.CreateChain("Track", chainTasks("Step 1", "Step 2"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	tasks, err := s.GetChainTasks(chain.ID)
+	if err != nil {
+		t.Fatal(err)
+	}
+	originalDueDate := *tasks[0].DueDate
+
+	// Pause and resume with nothing completed yet -- position 0 is already
+	// unlocked and should be left untouched by the resume catch-up.
+	if err := s.SetChainStatus(chain.ID, "paused"); err != nil {
+		t.Fatal(err)
+	}
+	if err := s.SetChainStatus(chain.ID, "active"); err != nil {
+		t.Fatal(err)
+	}
+
+	after, err := s.GetChainTasks(chain.ID)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !after[0].DueDate.Equal(originalDueDate) {
+		t.Errorf("DueDate = %v, want unchanged %v (resume catch-up should be a no-op when nothing was stuck)", after[0].DueDate, originalDueDate)
+	}
+}
+
 func TestGetUndatedNativeTasks_ExcludesLockedChainTasks(t *testing.T) {
 	s := newNativeTasksTestStore(t)