[cursor]

Problem

PATCH /v1/todos/:id (and batch PATCH) accept a non-terminal status (pending / in_progress), which is the HTTP reopen path. update_todo auto-stamped completed_at when moving to completed or canceled, but left the stamp in place on reopen.

Storage and docs say completed_at = 0 until terminal. A completed-then-reopened row kept a non-zero timestamp, so list/get JSON, UIs that treat completed_at > 0 as done, and any client filtering on that column were wrong. Subject/description edits on a still-terminal row were already correct (leave the stamp).

Writ /todo start only resolves against open rows, so this was HTTP-only — but PATCH is the supported reopen API.

Fix

When status is set and the caller did not pass completed_at:

• terminal → stamp now() (unchanged)
• non-terminal → write completed_at = 0

An explicit completed_at argument still overrides. Header, concept, and PATCH docs match the store.

Tests

unit_todos — reopen from completed→pending and canceled→in_progress clears the stamp; explicit override on reopen is honored; subject edit after completed does not clear. Suite 10/10 locally (+ ASan, 154 assertions). arbiter compiles.

Independently mergeable against main (0456350). merge-tree vs #321–#347: code auto-merges (update_todo / test_todos are disjoint from those hunks); only CHANGELOG [Unreleased] sibling-conflicts after the first of those merges.

  

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Note

Low Risk
Localized todo persistence and API contract fix with new unit tests; no auth or cross-tenant behavior changes.

Overview
Reopened todos now reset completed_at. TenantStore::update_todo (single and batch PATCH /v1/todos) used to stamp completed_at on completed/canceled but left the old timestamp when status moved back to pending or in_progress. That broke the documented rule that completed_at stays 0 until a terminal status.

When status is present and completed_at is omitted, non-terminal statuses now write completed_at = 0; terminal statuses still auto-stamp now(). An explicit completed_at in the request still wins. Subject/description-only updates on a terminal row do not touch the stamp.

Docs (PATCH API, todos concept) and CHANGELOG match the store. unit_todos adds reopen, override, and non-clearing edit cases.

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