feat: lifecycle role/hazard labels and canonical state mapping (#603)

Add orthogonal role:* (single-active owner) and hazard:* (additive warning)
lifecycle labels plus status:changes-requested, folding the #603 state:*
vocabulary into the canonical status:* set rather than a conflicting parallel
prefix.

- issue_workflow_labels.py: ROLE_/HAZARD_ specs + frozensets; role/hazard
  transition maps and helpers (transition_role_labels, add/clear_hazard_label,
  canonical_role_label, canonical_hazard_label, is_discussion,
  is_implementation_candidate, requires_blocking_reason); state:* -> status:*
  synonym transitions; assess_issue_labels surfaces role/hazard dims and flags
  multiple active role labels
- docs/label-taxonomy.md: role, hazard, state->canonical migration, and
  allocator cross-check sections
- tests: role/hazard/discussion/blocking-reason/state-synonym coverage
- manage_labels.py seeds the new labels automatically via CANONICAL_LABEL_SPECS

Labels remain advisory; control-plane leases (#601) and live PR state stay the
source of truth for mutations (#603 AC2).

Closes #603

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

docs/label-taxonomy.md

@@ -39,6 +39,7 @@ one.
 | `status:blocked` | Issue is blocked |
 | `status:needs-review` | Issue work needs review |
 | `status:pr-open` | A linked PR is open |
+| `status:changes-requested` | Reviewer requested changes on the linked PR |
 | `status:approved` | Linked PR is approved |
 | `status:merged` | Linked PR is merged |
 | `status:reconcile` | Issue needs reconciliation |
@@ -46,6 +47,72 @@ one.
 | `status:duplicate` | Issue is a duplicate |
 | `status:wontfix` | Issue will not be fixed |
 
+## Role Ownership Labels (#603)
+
+A single `role:*` label shows which workflow role currently owns the item. It is
+advisory visibility only — the control-plane lease (#601) is the source of truth
+for mutation authority. Only one `role:*` label is active at a time; tooling
+replaces it on handoff via `transition_role_labels`.
+
+| Label | Use |
+| --- | --- |
+| `role:author` | Author currently owns the item |
+| `role:reviewer` | Reviewer currently owns the item |
+| `role:merger` | Merger currently owns the item |
+
+## Hazard Labels (#603)
+
+Hazard labels are orthogonal warning flags. Unlike `status:*` and `role:*`,
+**more than one hazard may be active at once**, and a hazard never substitutes
+for a live lease / PR-state check. Add/remove with `add_hazard_label` /
+`clear_hazard_label`.
+
+| Label | Use |
+| --- | --- |
+| `hazard:stale-lease` | A stale or expired lease references this item |
+| `hazard:workflow-contaminated` | Session/workflow state is contaminated; do not mutate |
+| `hazard:conflicted` | Linked PR has merge conflicts |
+| `hazard:root-mutation` | Work was mutated in the project root checkout |
+| `hazard:manual-state` | Session or lease state was edited manually |
+| `hazard:terminal-blocker` | A terminal review/merge lock blocks progress (#332/#602) |
+
+Any item that carries `status:blocked` or any `hazard:*` flag must also have a
+blocking-reason / next-action comment (`requires_blocking_reason`).
+
+## `state:*` → canonical mapping (#603 migration)
+
+Issue #603 proposed a parallel `state:*` vocabulary. To avoid a conflicting
+second lifecycle prefix, those requested states are folded into the existing
+canonical labels rather than introduced as `state:*`. `state:*` is **not** a
+supported prefix; use the canonical label on the right.
+
+| Requested `state:*` | Canonical label |
+| --- | --- |
+| `state:needs-triage` | `status:triage` |
+| `state:claimed` | `status:claimed` |
+| `state:authoring` | `status:in-progress` |
+| `state:needs-review` | `status:needs-review` |
+| `state:reviewing` | `status:needs-review` |
+| `state:changes-requested` | `status:changes-requested` |
+| `state:approved` | `status:approved` |
+| `state:merge-ready` | `status:approved` |
+| `state:merged` | `status:merged` |
+| `state:blocked` | `status:blocked` |
+| `state:terminal-blocker` | `hazard:terminal-blocker` |
+| `state:abandoned` | `status:wontfix` |
+
+The transition helpers accept these names as synonyms (e.g.
+`canonical_status_label("authoring")` → `status:in-progress`), so callers may use
+the #603 wording while a single canonical status stays active.
+
+## Allocator Cross-Check (#603)
+
+Labels are advisory queue hints. The work allocator (#600/#613) uses labels as
+one signal but **cross-checks live leases and PR state** and never trusts labels
+alone. Discussion issues (`type:discussion`) are excluded from implementation
+queues (`is_implementation_candidate`) unless a controller explicitly selects
+them.
+
 ## Transition Rules
 
 Suggested lifecycle: