[6/7] Record task status transitions

[alex-clickhouse]

Stacked on #276 → #275 → #274 → #273 → #272 → main.

The gap

Nerve kept no history of status changes. tasks holds only the current value, memu_audit_log is memU-only, session_events is sessions. The markdown ## Updates list was the closest thing, and it only gains a line when a note is passed or on done/reopen:

Transition	Recorded before?
task_update(note="…")	✅ - 2026-08-05: <note>
task_done / reopen	✅
plain status flip	❌ nothing

So pending → in_progress → deferred → in_progress left no evidence it happened. Even the lines that were written are day-granularity with no actor.

Tolerable while status changes were rare and deliberate. The board makes them a drag — and /move routes through exactly that note-less path, so every drag was an untracked mutation. A board is also what prompts the questions this answers: how long has this been in progress, which cards are aging, how often does work bounce back out of review.

What's here

task_events (task_id, from_status, to_status, actor, created_at), seeded with one origin row per existing task. from_status is NULL for a creation, so aging can distinguish "created here" from "moved here".

Recording happens in the same transaction as the status write, from all three paths that can change one:

• update_task_status
• move_task
• the full-row upsert_task — which is how task_update flips status when it also writes a note, and would otherwise have been a silent gap

The rule that makes it work

A no-op transition records nothing. That single check is what keeps the table meaningful rather than merely large:

• reindex() rewrites every row on startup through that same upsert, with the status it already had. Without the check, history would double on every run.
• A pure reorder within a lane is the most frequent board interaction there is, and changes no status.

The one case where reindex does change a status — resetting an orphaned row to match its directory — is a genuine correction and gets a row. Both directions are pinned in test_task_events.py.

Actor

Session id for agent-driven changes, web for the HTTP API. The task routes now build their tool context with that name instead of the generic "system" sentinel — build_route_tool_context already took the parameter; nothing else keys off the old value.

UI

• Aging badge on board cards after 3 days in a status (amber at 7, red at 14). Coarse on purpose: the signal is "this has stalled", and a badge on every card would be noise.
• History panel in the task detail view — each transition with its dwell time, which is the part that actually explains why something took as long as it did.

Tasks whose last change predates this table report no entry time rather than a guessed one, so the indicator stays silent instead of showing an age that isn't true.

Testing

• pytest tests/ -q — 3095 passed (22 new)
• npm test — 46 passed · tsc -b clean · npm run build clean
• npx eslint . — 148 vs 152 on main

Open questions from the task write-up, deliberately unanswered here

• Retention — unbounded today. Worth wiring into db/retention.py if this grows, though at a few rows per task per week it's a long way off.
• Backfill from the markdown ## Updates lines — not attempted. The dates are day-granularity and the format is loose; a fabricated timeline that looks precise seemed worse than starting clean.
• Scope — status-only. Title/tag/deadline edits aren't recorded; folding them in would want a different shape (field, old, new) and is a bigger conversation.

🤖 Generated with Claude Code

[Copilot]

Pull request overview

Adds first-class, append-only task status transition history to Nerve (task_events) and surfaces it through the API and UI to support “card aging” on the board and a per-task status timeline.

Changes:

• Introduces task_events (migration v044) and records transitions transactionally from upsert_task, update_task_status, and move_task, including an actor.
• Adds backend APIs to fetch task event history and to return status_since in the board payload for aging badges.
• Adds frontend UI for a task status history panel and aging indicators on board cards, plus client/store wiring.

Reviewed changes

Copilot reviewed 16 out of 16 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
web/src/stores/taskStore.ts	Stores/loads statusSince from board API response.
web/src/stores/taskStore.test.ts	Updates board API mocks to include status_since.
web/src/components/Tasks/TaskTimeline.tsx	New timeline component fetching and rendering task status events + dwell time.
web/src/components/Tasks/TaskDetailBody.tsx	Adds toggleable “status history” panel in task detail UI.
web/src/components/Tasks/Board/TaskBoard.tsx	Plumbs statusSince from store into board columns.
web/src/components/Tasks/Board/BoardColumn.tsx	Passes per-task statusSince down to cards.
web/src/components/Tasks/Board/BoardCard.tsx	Adds aging badge based on statusSince thresholds.
web/src/api/client.ts	Adds TaskEvent type, listTaskEvents(), and status_since typing for board response.
tests/test_task_events.py	New unit tests covering transition recording + no-op suppression + entry-time computation.
tests/test_task_board_api.py	Adds HTTP-level tests for /events and status_since presence on board.
nerve/gateway/routes/tasks.py	Adds /api/tasks/{id}/events and includes status_since in board response; sets web actor.
nerve/db/tasks.py	Records status events and computes per-task status entry timestamps for aging.
nerve/db/migrations/v044_task_events.py	Creates task_events table + indexes and seeds origin events for existing tasks.
nerve/agent/tools/handlers/tasks.py	Propagates actor/session id into DB status changes and upserts.
docs/tasks.md	Documents the new status history table and its recording rules.
docs/api.md	Documents new status_since board field and GET /api/tasks/{id}/events.

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