fix(author): unify the bootstrap and lock_issue issue-lock contract (Closes #953)

gitea_bootstrap_author_issue_worktree wrote a lock no downstream author
operation accepts, then directed the author straight to implementation. Once
the branch carried commits, heartbeat, re-lock, exact-owner renewal, and the
#447 create-PR guard all refused simultaneously and no sanctioned recovery
path remained eligible.

Each of those gates is individually correct. The defect was that two writers
disagreed about what a lock is.

- Add author_lock_contract as the single canonical definition: claimant,
  work_lease, lock_provenance, generation, and an explicit expiration state.
  Both gitea_lock_issue and bootstrap now build through it.
- Promote issue_lock_store.lock_claimant to the one shared claimant reader and
  use it in the ownership check, so a claimant recorded at the lock top level
  is read rather than refused. The values are still compared against
  server-resolved identity and profile, so no legacy placement grants anything
  the canonical placement would not.
- Represent missing expiration explicitly. An absent expires_at previously read
  as "not yet expired", leaving a malformed lock permanently non-expiring and
  permanently ineligible for #760 renewal.
- Bootstrap reads its lock back and verifies it structurally before reporting
  success. A partial lock fails closed while the worktree is still
  base-equivalent, names the missing fields, and never reports
  implementation_allowed. Its exact_next_action now matches the state returned.
- Add gitea_recover_incomplete_bootstrap_lock for locks already written by the
  old bootstrap, including those whose branches carry pushed commits. It never
  moves, resets, or rewinds a branch, never requires base-equivalence, never
  pushes or opens a PR, and touches only the target lock. It proves repository,
  issue, claimant username and profile, branch, worktree, registration, and
  head before writing, refuses healthy foreign-owned locks, and mints
  provenance and authorization server-side.
- Add gitea_inspect_issue_lock_contract, a strictly read-only surface.
- Document the required ordering and the recovery path.

The #447 provenance guard is unchanged and the sanctioned source set was not
widened: bootstrap now satisfies the guard rather than the guard being relaxed
to admit bootstrap.

Tests: 61 new cases covering the canonical schema, immediate heartbeat,
renewal before and after commits, the create_pr guard, executable next actions,
partial and malformed and missing-expiration and expired and same-owner and
foreign-owner and legacy locks, recovery isolation, read-only inspection, and
the full bootstrap-implement-commit-push-create_pr regression against isolated
fixtures.

Full suite at head: 28 failed, 5753 passed, 6 skipped, 1042 subtests.
Full suite at base 82d71b77: 28 failed, 5692 passed, 6 skipped, 1042 subtests.
Failing test-ID sets are identical, so there are zero regressions; the +61
passes are this issue's new suite.

Issue #949 was preserved and not recovered: its branch remains at
92615f474b and its worktree, lock, and PR state
were not touched. The #949-shaped regression uses isolated fixtures only.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

docs/author-issue-lock-contract.md

@@ -0,0 +1,148 @@
+# The canonical author issue-lock contract (#953)
+
+Every author issue lock has exactly one shape. Both writers —
+`gitea_bootstrap_author_issue_worktree` and `gitea_lock_issue` — build it
+through `author_lock_contract.build_canonical_issue_lock`, and every reader
+consumes that same shape.
+
+Before #953 the two writers disagreed. `gitea_lock_issue` wrote the canonical
+record; bootstrap wrote a thinner one with the claimant at the lock top level,
+`lease_id: null`, and no `work_lease`, `lock_provenance`, or expiry. Because
+every reader was written against the canonical shape, a lock that bootstrap
+reported as successfully created could not be heartbeated, renewed, re-locked,
+or accepted by `gitea_create_pr`. Each of those gates was individually correct;
+the defect was that two writers disagreed about what a lock *is*.
+
+## Required ordering
+
+**Finalize the lock before writing any implementation bytes.** This ordering is
+what keeps recovery cheap: while the worktree is still base-equivalent, a lock
+problem can be fixed by simply calling `gitea_lock_issue` again. Once the branch
+carries commits, base-equivalence is gone and the ordinary re-lock path is no
+longer available.
+
+1. `gitea_whoami` — resolve identity and profile.
+2. `gitea_resolve_task_capability(task='work_issue')`.
+3. `gitea_bootstrap_author_issue_worktree` — creates the branch, the registered
+   worktree under `branches/`, and a **canonical** lock. It reads the lock back
+   and verifies it structurally before reporting success; a partial lock fails
+   closed here, with the missing fields named, and never reports
+   `implementation_allowed: true`.
+4. `gitea_heartbeat_issue_lock` — prove the lock is usable, using the
+   `task_session_id` bootstrap returned.
+5. Implement, commit, push.
+6. `gitea_create_pr`.
+
+If bootstrap returns `success: false` with
+`reason_code: incomplete_issue_lock_contract`, **do not implement**. Its
+`exact_next_action` names the executable recovery step. Bootstrap's reported
+next action always matches the state it actually returned.
+
+## The contract
+
+A canonical lock carries every field in
+`author_lock_contract.REQUIRED_LOCK_FIELDS`:
+
+| Field | Meaning |
+| --- | --- |
+| `remote`, `org`, `repo`, `issue_number` | repository and issue identity |
+| `branch_name`, `worktree_path` | the binding this claim owns |
+| `work_lease` | the canonical lease block, below |
+| `lock_provenance` | sanctioned source, minted server-side |
+| `lock_generation` | monotonic; every write advances it |
+
+`work_lease` carries every field in
+`author_lock_contract.REQUIRED_WORK_LEASE_FIELDS`, notably:
+
+| Field | Meaning |
+| --- | --- |
+| `claimant.{username,profile}` | **canonical** claimant placement |
+| `expires_at` | sliding TTL from `lease_policy` |
+| `last_heartbeat_at`, `heartbeat_count` | liveness evidence |
+| `task_session_id` | the ownership fencing token — never null |
+| `lifecycle_version` | `heartbeat-v1`; its absence is what makes a lock legacy |
+
+### Claimant placement and legacy compatibility
+
+`work_lease.claimant` is canonical. A top-level `claimant` is the legacy
+placement written by pre-#953 bootstrap and is still **read** — through the one
+shared reader, `issue_lock_store.lock_claimant` — so an existing lock is not
+refused for "not recording a claimant" when it plainly records one.
+
+Tolerating the placement is not a widening. Every caller still compares the
+values against server-resolved identity and profile, so a legacy placement
+grants nothing the canonical placement would not. When both are present, the
+`work_lease` copy wins: after an upgrade, a stale top-level copy must never
+decide ownership.
+
+### Expiration is explicit
+
+A lock with no recorded expiry is **not** "not yet expired". `is_lease_expired`
+returns `False` for it, which used to make such a lock permanently non-expiring
+*and* permanently ineligible for #760 exact-owner renewal, which only ever
+assesses an expired lease. `author_lock_contract.expiration_state` names the
+real fact: `recorded`, `missing`, or `unparseable`. A `missing` expiry makes the
+lock eligible for the recovery path below rather than stranding it.
+
+## Recovering an existing incomplete bootstrap lock
+
+For locks already written by the old bootstrap — including those whose branches
+already carry legitimate committed and pushed work — use:
+
+```text
+gitea_inspect_issue_lock_contract(issue_number, branch_name, worktree_path, remote=...)
+gitea_recover_incomplete_bootstrap_lock(issue_number, branch_name, worktree_path, expected_head, remote=...)
+```
+
+`gitea_inspect_issue_lock_contract` is strictly read-only: it performs no lock,
+lease, branch, worktree, issue, or pull-request mutation. Use it first to see
+which fields are missing and what the recommended action is; pass `dry_run=True`
+to the recovery tool to preview the decision without writing.
+
+`gitea_recover_incomplete_bootstrap_lock` upgrades that one lock to the
+canonical contract. Before writing anything it verifies:
+
+* repository (`remote`, `org`, `repo`) and issue number
+* claimant username **and** profile against the server-resolved values — a
+  matching username alone is never accepted
+* branch, worktree path, worktree existence, and worktree registration
+* the worktree is on the recorded branch
+* the observed head equals the caller's `expected_head`
+* the existing lock's generation and provenance state
+* the absence of healthy foreign ownership
+
+What it deliberately does **not** do:
+
+* it never moves, resets, or rewinds the branch, and never requires
+  base-equivalence — preserving the committed work is the entire point;
+* it never pushes and never creates a pull request;
+* it touches only the single lock file for that exact remote/org/repo/issue;
+* it accepts no caller-supplied provenance and no caller-supplied authorization
+  flag — both are minted server-side.
+
+A recovered lock records a `bootstrap_lock_recovery` block holding both sides of
+the transition — prior contract, prior missing fields, prior generation, prior
+owning session, the replacement `task_session_id`, and the preserved head — so a
+recovered claim never reads as an original one.
+
+### Refusals
+
+| `refusal_code` | Meaning |
+| --- | --- |
+| `no_durable_lock` | nothing to recover |
+| `already_canonical` | lock is fine; rewriting would invalidate a live heartbeat token |
+| `foreign_claimant` | recorded claimant is not the active identity/profile pair |
+| `healthy_foreign_lock` | a live foreign-owned lock; takeover is not a recovery path |
+| `identity_unresolved` | identity or profile could not be resolved |
+| `binding_mismatch` | repository, issue, branch, or worktree does not match |
+| `worktree_invalid` | worktree missing, unregistered, or on another branch |
+| `head_mismatch` | the worktree moved under the caller |
+
+## The #447 create-PR provenance guard is unchanged
+
+`issue_lock_provenance.assess_lock_file_for_create_pr` still requires both a
+sanctioned `lock_provenance` and a `work_lease`, and the sanctioned source set
+was **not** widened. Bootstrap writes through
+`issue_lock_provenance.SOURCE_LOCK_ISSUE` — the lock it produces *is* a
+canonical lock, not a second dialect with its own exemption. Bootstrap now
+satisfies the guard rather than the guard being relaxed to admit bootstrap.