Implement linear task chains and recurring maintenance buckets

Backend, web timeline, and Android widget wiring for the last two
unimplemented items from doot-future-task-scheduling-ideas.

Chains: task_chains table + chain_id/chain_position/chain_unlocked on
native_tasks (migration 026), WIP-limit-1 advancement hooked into
CompleteNativeTask, locked tasks excluded from all date-based queries,
5 new /api/widget/chains* endpoints, an N/M position badge on web and
Android widget rows.

Buckets: maintenance_buckets table + bucket_id/bucket_state/
bucket_last_active_at on native_tasks (migration 027),
staleness-then-priority selection scoring, a new RunBucketCycleCheck
scheduler loop, 5 new endpoints including the distinct Defer action, a
Defer button on web and Android widget rows.

Also corrected stale "not yet approved" status headers on the two
already-shipped specs this work depended on (labels/projects, budgets/
availability) -- their headers were never updated after implementation.

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

1 files changed, 22 insertions, 0 deletions

diff --git a/internal/handlers/timeline_logic.go b/internal/handlers/timeline_logic.go
index b90b61e..e3da760 100644
--- a/internal/handlers/timeline_logic.go
+++ b/internal/handlers/timeline_logic.go
@@ -12,6 +12,22 @@ import (
 	"task-dashboard/internal/store"
 )
 
+// setChainBadge populates item.ChainPosition/ChainTotal (1-indexed) when
+// task belongs to a chain. Only the currently-unlocked task in a chain ever
+// reaches BuildTimeline (locked tasks are excluded at the store layer), so
+// this runs at most once per chain per call -- no memoization needed.
+func setChainBadge(s *store.Store, item *models.TimelineItem, task models.Task) {
+	if task.ChainID == "" {
+		return
+	}
+	tasks, err := s.GetChainTasks(task.ChainID)
+	if err != nil {
+		return
+	}
+	item.ChainPosition = task.ChainPosition + 1
+	item.ChainTotal = len(tasks)
+}
+
 // BuildTimeline aggregates and normalizes data into a timeline structure
 func BuildTimeline(ctx context.Context, s *store.Store, start, end time.Time) ([]models.TimelineItem, error) {
 	var items []models.TimelineItem
@@ -159,6 +175,8 @@ func BuildTimeline(ctx context.Context, s *store.Store, start, end time.Time) ([
 				Source:       "doot",
 				ProjectColor: projectColors[task.ProjectID],
 			}
+			setChainBadge(s, &item, task)
+			item.BucketState = task.BucketState
 			item.ComputeDaySection(now)
 			items = append(items, item)
 		}
@@ -183,6 +201,8 @@ func BuildTimeline(ctx context.Context, s *store.Store, start, end time.Time) ([
 				Source:       "doot",
 				ProjectColor: projectColors[task.ProjectID],
 			}
+			setChainBadge(s, &item, task)
+			item.BucketState = task.BucketState
 			item.ComputeDaySection(now)
 			items = append(items, item)
 		}
@@ -205,6 +225,8 @@ func BuildTimeline(ctx context.Context, s *store.Store, start, end time.Time) ([
 				IsAllDay:     true,
 				ProjectColor: projectColors[task.ProjectID],
 			}
+			setChainBadge(s, &item, task)
+			item.BucketState = task.BucketState
 			item.ComputeDaySection(now)
 			items = append(items, item)
 		}