feat(author-workflow): enforce exact issue lock before branch/commit/push/PR (Issue #204)

Recreation of the #204 work from closed PR #205 (invalid provenance), rebuilt
cleanly on master under the prgs author identity with no PR #203 content:

- Add gitea_lock_issue MCP tool: locks exactly one issue to its branch name,
  fails closed on branch/issue-number mismatch and on issues already tied to
  an open PR (by head branch or Closes/Fixes reference).
- gitea_create_pr now requires the issue lock: head must match the locked
  branch, title/body must contain Closes/Fixes #<locked issue> exactly, and
  ambiguous references (equivalent / related / same as) are rejected.
- scripts/worktree-start refuses to create an issue-linked worktree unless the
  lock file exists and matches the requested branch.
- assess_controller_handoff rejects handoffs whose selected issue / opened PR
  fields carry multiple numbers or fuzzy equivalence wording.
- Tests: TestIssueLocking (lock + create_pr gates), handoff exact-reference
  tests, worktree-start lock coverage.

Closes #204

Co-Authored-By: Claude Fable 5 <[email protected]>

review_proofs.py

@@ -846,6 +846,35 @@ def assess_controller_handoff(report_text, role=None):
             "reasons": [f"handoff missing required field: {m}"
                         for m in missing],
         }
+
+    # Validate issue/PR references for exact number and no forbidden terms (Issue #194 / #196)
+    fields_dict = {}
+    for line in section:
+        stripped = line.strip().lstrip("-*").strip()
+        if ":" in stripped:
+            k, v = stripped.split(":", 1)
+            fields_dict[k.strip().lower()] = v.strip()
+
+    for alias in ("selected issue", "pr number opened", "pr opened", "pr number", "selected pr"):
+        val = fields_dict.get(alias)
+        if val:
+            numbers = re.findall(r"\d+", val)
+            has_forbidden = any(term in val.lower() for term in ("equivalent", "related", "same", "/"))
+            if len(numbers) != 1 or has_forbidden:
+                field_name = "Selected issue/PR"
+                for name, aliases in list(HANDOFF_BASE_FIELDS) + list(HANDOFF_ROLE_FIELDS.get(role or "", ())):
+                    if alias in aliases:
+                        field_name = name
+                        break
+                return {
+                    "verdict": "incomplete",
+                    "downgraded": True,
+                    "missing_fields": [field_name],
+                    "reasons": [
+                        f"{field_name} must specify exactly one number and no ambiguous references (got: '{val}')"
+                    ],
+                }
+
     return {
         "verdict": "complete",
         "downgraded": False,