fix: clarify capability preflight lifetime across safe reads (Closes #470)

Add preflight_contract helpers with explicit re-resolve error messages,
document the read-only tool set and consumption rules, and extend tests
for close_pr sequencing and task replacement.

Validation: ./venv/bin/python -m pytest tests/test_preflight_read_survival.py tests/test_mcp_server.py::TestPreflightVerification -q

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

docs/llm-workflow-runbooks.md

@@ -459,6 +459,25 @@ Root-level matches are listed in `.gitignore` so they never get committed.
 `gitea_get_runtime_context` and `gitea_lock_issue` surface **warnings** (not
 hard blocks) when these artifacts are still present.
 
+## Capability preflight lifetime (#470)
+
+After `gitea_resolve_task_capability(task=…)` proves the mutation is allowed,
+interleaved **read-only** calls preserve that proof until a gated mutation
+consumes it:
+
+- Safe reads: `gitea_whoami`, `gitea_view_pr`, `gitea_view_issue`, `gitea_list_*`,
+  `gitea_get_runtime_context`, `gitea_check_pr_eligibility`, and related
+  read-only inventory/eligibility tools (see `preflight_contract.py`).
+- Each mutation consumes the proof once; call `gitea_resolve_task_capability`
+  again immediately before the next mutation on the same task.
+- Resolving capability for a **different** task replaces the prior task binding.
+- Workspace edits before resolve, profile switches, or a dirty whoami baseline
+  invalidate proof (fail closed).
+
+If a mutation fails with “capability has not been resolved” or “task mismatch”,
+re-run `gitea_resolve_task_capability(task="<mutation>")` immediately before
+retrying — do not guess or skip the resolve step.
+
 Implementation work and review work must use separate branch folders. For
 example, an implementation branch might live under
 `branches/fix-issue-123-example`, while a review branch for the resulting PR