task new waits for a milestone the listing has not caught up with (#243)

[radiusred-cody]

Closes #243
Closes #234

What was done

task new --milestone <n> no longer trusts a single read of the open-milestone listing. When the listing lacks M<n> it:

1. reads the hub's newest issues regardless of label (RecentIssues, in the tracker since milestone new never reuses a milestone number #209) and accepts an open M<n>: issue that carries cc:milestone — confirmed on the issue itself through the existing Task(ref) fetch, since that listing is unfiltered and shows closed issues;
2. failing that, waits 2s and reads both again — three reads in all — before refused[NOT_FOUND], whose detail now says the listing can lag a milestone created seconds ago.

A milestone found by either fallback is printed as a note, so the run's output records that the listing lagged. The sleeper is a package func var (sleep = time.Sleep, the ghVersion pattern) so the tests record the waits instead of taking them. The common case — the number is in the listing — is unchanged at one read.

Tests (internal/cli/task_test.go, fake tracker with successive listing answers): fresh listing → one read, no wait, no note; stale-then-fresh → success after two recorded 2s waits with the note; found among the newest issues → success with no wait, and a closed M<n>: milestone or a plain issue titled M<n>: is not accepted; never found → NOT_FOUND after exactly three reads with the two waits recorded, nothing created.

Docs: roles/coordinator.md (the back-to-back milestones line: a task new right after milestone new may take a moment and retries itself; do not script a pause around it), SPEC.md §6 task new row, docs/introduction.md NOT_FOUND line, CHANGELOG.md under [Unreleased].

Requirements

M12-R2 (milestone #241).

Record

• Decision (fallback order, confirmation through Task, bounded retries, the rejected alternatives): task new waits for a milestone the listing has not caught up with #243 (comment)
• No deviations from the plan.

🤖 Generated with Claude Code

https://claude.ai/code/session_01QsJKZXNhs7rsovhb6jXCRE

[radiusred-checky]

Approved. I reviewed the diff before the PR body, then checked task #243, milestone #241/M12-R2, historical milestone #207 context, and capture #234 including its Correction comment. The implementation matches the requirement: bounded retry/fallback before NOT_FOUND, injectable sleep, no test waits, and fallback validation rejects closed or non-cc:milestone issues. Record and docs are in step: task plan and Decision precede the commits, PR body closes #243 and #234, coordinator/SPEC/introduction/changelog are updated, and the changelog entry is under the new Unreleased heading ending (#243). Verification run with repo-local caches: go test ./..., go vet ./..., gofmt -l ., go build -o ./gh-codecrew ./cmd/codecrew, plus read-only probes of the changed NOT_FOUND path and status.