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, 13 insertions, 0 deletions

diff --git a/internal/handlers/handlers.go b/internal/handlers/handlers.go
index 343d0b1..54c6a70 100644
--- a/internal/handlers/handlers.go
+++ b/internal/handlers/handlers.go
@@ -3,6 +3,7 @@ package handlers
 import (
 	"context"
 	"crypto/rand"
+	"errors"
 	"fmt"
 	"html/template"
 	"log"
@@ -46,6 +47,7 @@ func New(s *store.Store, trello api.TrelloAPI, planToEat api.PlanToEatAPI, googl
 	// Template functions
 	funcMap := template.FuncMap{
 		"subtract": func(a, b int) int { return a - b },
+		"add":      func(a, b int) int { return a + b },
 		// multiDayLabel returns the "(starts/ends HH:MM)" suffix for a
 		// multi-day calendar event's row on the day it's rendered, or ""
 		// for a normal item or a "spans" (pass-through) day, which shows
@@ -580,6 +582,10 @@ func (h *Handler) handleAtomToggle(w http.ResponseWriter, r *http.Request, compl
 	}
 
 	if err != nil {
+		if errors.Is(err, store.ErrChainTaskLocked) {
+			JSONError(w, http.StatusBadRequest, "Task is locked in its chain", err)
+			return
+		}
 		action := "complete"
 		if !complete {
 			action = "reopen"
@@ -858,6 +864,11 @@ func (h *Handler) HandleTabTasks(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	chainSummaries, err := BuildChainSummaries(h.store)
+	if err != nil {
+		log.Printf("Warning: failed to build chain summaries: %v", err)
+	}
+
 	SortAtomsByUrgency(atoms)
 	currentAtoms, futureAtoms := PartitionAtomsByTime(atoms)
 
@@ -865,11 +876,13 @@ func (h *Handler) HandleTabTasks(w http.ResponseWriter, r *http.Request) {
 		Atoms       []models.Atom
 		FutureAtoms []models.Atom
 		Boards      []models.Board
+		Chains      []models.ChainSummary
 		Today       string
 	}{
 		Atoms:       currentAtoms,
 		FutureAtoms: futureAtoms,
 		Boards:      boards,
+		Chains:      chainSummaries,
 		Today:       config.Now().Format("2006-01-02"),
 	}