v1.21.0 — identifier-form completion URLs route the diff correctly, and a release runbook

Fixed — an identifier-form completion URL no longer routes the diff through a stale claim cache (D309)

taskIdFromCommand read only a numeric id, while the server also resolves /api/tasks/<identifier>/complete. A completion URL such as /api/tasks/W2185/complete therefore resolved no id and the changed_files upload fell back to the claim-derived env cache, which still holds the previous task when the claim response was concealed — so the diff landed on that task with a 2xx and no error. The regex now accepts a numeric id or a G/W/D identifier, still tail-anchored and still returning "" on any other segment, so the numeric path is unchanged. The closed class keeps the captured id safe to interpolate into the PUT path, and the env-cache fallback stays for ids that are not literal in the command.

Added — what this extension is, and is not, exposed to by a hidden API response (W2185, W2187)

ADR-002 gains an addendum, and the README a canon-anchored paragraph, recording the split verdict on the fleet's stdout-preservation curl guard: the diff's content is not exposed, because the snapshot comes from git and the upload is this extension's own fetch(), but its destination was. Since D309 both say the identifier case is closed and name the two shapes that still reach the cache — a shell-expanded id and a literal segment in neither accepted form.

Added — a release runbook for this repository (W2173)

RELEASE.md records how this repository is released, as its own history shows it: which file holds the version, the changelog's shape (and that it has changed over time), that there is no catalog to sync, and the one-line check for whether the changelog's top heading is already tagged. Documentation only.