Offline write-queue: coalesce + replay without duplicating (#33)

While gitea is unreachable, propose-approved writes queue instead of being lost;
on reconnect they replay in order. The hard requirement is no duplication.

The mechanism is coalescing by axis. Every write targets one field of one issue
(estimate / priority / assignee / milestone), so `issue:kind` is the axis identity.
Queuing a second write to the same axis supersedes the first (moved to the tail),
so a burst of edits replays as one final write — and replay is idempotent (the
apply path no-ops a change already reflected server-side).

- `enqueueWrite` (coalesce), `pendingWrites`, `coalesceKey`, `affectedIssues`
  (what a post-replay reconcile re-reads), and `replayQueue(queue, apply)` which
  drains through the same guarded write path and returns the writes that still
  failed so they stay queued. Never throws — a failure is data.

Acceptance met: a burst of offline edits + reconnect lands the final state with a
single apply per axis (not one per edit); still-failing writes stay queued. +4
core tests; typecheck green.

Follow-up: persist the queue in main + trigger replay on the reconnect signal
(the offline banner + disabled composer already exist) — the coalesce/replay
core is the tested heart.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

packages/core/src/queue/write-queue-v0.test.ts

@@ -0,0 +1,67 @@
+import { describe, expect, it, vi } from 'vitest'
+
+import type { IssueChange } from '../changes/apply-changes-v0.js'
+import { affectedIssues, coalesceKey, enqueueWrite, pendingWrites, replayQueue, type QueuedWrite } from './write-queue-v0.js'
+
+const reest = (issue: number, estimate: string): IssueChange =>
+  ({ kind: 'reestimate', issue, estimate }) as IssueChange
+const assign = (issue: number, assignee: string | null): IssueChange => ({ kind: 'assign', issue, assignee })
+
+describe('write-queue-v0 (#33)', () => {
+  it('coalesces repeat writes to the same (issue, axis) — replay applies the latest once', () => {
+    let q: QueuedWrite[] = []
+    q = enqueueWrite(q, reest(7, 'est/2d'), '2026-02-10T09:00:00Z')
+    q = enqueueWrite(q, reest(7, 'est/5d'), '2026-02-10T09:05:00Z') // supersedes est/2d
+    q = enqueueWrite(q, assign(7, 'christian'), '2026-02-10T09:06:00Z') // different axis — kept
+
+    expect(q).toHaveLength(2)
+    const pending = pendingWrites(q)
+    expect(pending).toEqual([
+      { kind: 'reestimate', issue: 7, estimate: 'est/5d' },
+      { kind: 'assign', issue: 7, assignee: 'christian' },
+    ])
+    expect(coalesceKey(reest(7, 'est/2d'))).toBe('7:reestimate')
+  })
+
+  it('keeps writes to different issues and axes distinct', () => {
+    let q: QueuedWrite[] = []
+    q = enqueueWrite(q, reest(7, 'est/2d'), 't1')
+    q = enqueueWrite(q, reest(8, 'est/3d'), 't2')
+    q = enqueueWrite(q, assign(8, null), 't3')
+    expect(q).toHaveLength(3)
+    expect(affectedIssues(q)).toEqual([7, 8])
+  })
+
+  it('a burst of edits then reconnect lands the final state without duplicating', async () => {
+    let q: QueuedWrite[] = []
+    // offline: three edits to #7's estimate, one assign
+    q = enqueueWrite(q, reest(7, 'est/1d'), 't1')
+    q = enqueueWrite(q, reest(7, 'est/2d'), 't2')
+    q = enqueueWrite(q, reest(7, 'est/8d'), 't3')
+    q = enqueueWrite(q, assign(7, 'stephen'), 't4')
+
+    const apply = vi.fn(async () => ({ ok: true }))
+    const { drained, remaining } = await replayQueue(q, apply)
+
+    // only the final estimate + the assign are applied — not three estimate writes
+    expect(apply).toHaveBeenCalledTimes(2)
+    expect(apply).toHaveBeenNthCalledWith(1, { kind: 'reestimate', issue: 7, estimate: 'est/8d' })
+    expect(apply).toHaveBeenNthCalledWith(2, { kind: 'assign', issue: 7, assignee: 'stephen' })
+    expect(remaining).toHaveLength(0)
+    expect(drained).toHaveLength(2)
+  })
+
+  it('keeps writes that still fail on reconnect queued (never throws)', async () => {
+    let q: QueuedWrite[] = []
+    q = enqueueWrite(q, reest(7, 'est/2d'), 't1')
+    q = enqueueWrite(q, reest(8, 'est/3d'), 't2')
+    // #7 applies, #8 rejects (still unreachable) — and one apply throws
+    const apply = vi.fn(async (c: IssueChange) => {
+      if (c.issue === 8) throw new Error('offline')
+      return { ok: true }
+    })
+    const { drained, remaining } = await replayQueue(q, apply)
+    expect(drained.map((w) => w.change.issue)).toEqual([7])
+    expect(remaining.map((w) => w.change.issue)).toEqual([8])
+  })
+})