[glennfaison]

Closes #69

What changed

• claim and renew (lib.sh) now go through _write_lease: if this account already wrote a lease comment for the same step on the item, it is edited in place (PATCH); otherwise one is posted. Three claims of a step leave one lease comment. Each step keeps its own comment. A comment from another account is never edited, and if the edit fails a new comment is posted, so the fallback is only noisier.
• Because a comment's position in the thread no longer says which lease is newest, lease_live (lib.sh) and leaseState (helpers.mjs) now take the lease written last (updated_at, else created_at, else thread order). Without this, re-claiming an earlier step's comment while a later step's comment sat after it would read the wrong expiry.
• The expiry is still the expires= inside the marker. The comment's edit time only orders leases and is never read as an expiry (the check the issue asked for), and a unit test covers a lease edited a minute ago whose marker expired an hour ago.
• New ownLeaseComment and an own-lease CLI command in helpers.mjs, so the shell and a no-shell runner share one implementation. NO_SHELL_OPS and the protocol's Leases and Markers sections are updated.
• Changeset added.

Tests

• tests/lib.test.sh: stub gh now supports PATCH of a comment, comment ids and timestamps. New cases for one comment after three claims, the newest expiry, a separate comment per step, renew editing in place, another account's comment untouched, the failed-edit fallback, and last write beats thread order. The existing expiry and trust tests pass unchanged.
• Shared fixtures (markers.json) gain two ordering cases that both the shell and Node suites run. helpers.test.mjs covers ownLeaseComment, the CLI and the edit-time-is-not-expiry case.
• Checked that the new shell tests fail against the previous lib.sh (5 failures) and pass with this change.
• Locally: bash tests/lib.test.sh 168 passed, node --test 376 passed, npm run validate, lint, sync:check and check-plugin-version all clean.

Notes

• Existing items keep the lease comments older runs posted; the next claim edits the last one for that step, so threads stop growing from then on. Old comments are not deleted.
• The scenario checker models a claim as a comment effect with the agent:lease marker. That is unchanged here, since scenario worlds start without lease comments.