feat: block issue closure on unproven expected pre-existing failure (#529)

Delivers #529 acceptance criterion 6: controller issue closure must be
blocked when the closure report calls a non-zero test-suite exit an
"expected pre-existing"/baseline failure without pre-merge proof.

- controller_closure_baseline_proof.py: assess_controller_closure_baseline_proof
  reuses the #533 pre-merge baseline verifier; empty report -> skipped/allowed,
  clean pass -> allowed, proven baseline -> allowed, unproven baseline -> block.
- gitea_close_issue: optional closure_report param; fails closed (no state PATCH)
  when the gate blocks.
- final_report_validator: new controller_close task kind (alias close_issue)
  wired to the pre-merge baseline proof rule so a closure can be pre-checked.
- Tests: tests/test_controller_closure_baseline_proof.py plus two
  gitea_close_issue gate tests.

Scope: criteria 2/3 (non-zero exit not a clean pass; baseline claims need
proof) are already enforced on master via premerge_baseline_proof (#533) and
the reviewer schema rules. Criteria 1/4/5 (post-merge moot canonical wording
and validation:* process-state labels) remain follow-up work.

Validation: full suite 2365 passed, 6 skipped; the 9 remaining failures
(tests/test_config.py TestAuthIntegration, tests/test_credentials.py
TestGetCredentials, test_issue_540 reviewer-role) are baseline-proven —
identical failures on clean prgs/master 6913ac9 (keychain/env dependent),
unrelated to this change.

Refs #529

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

controller_closure_baseline_proof.py

@@ -0,0 +1,63 @@
+"""Controller-closure baseline-proof gate (#529, criterion 6).
+
+A controller (or any session) may close a tracking issue with a closure
+report that summarizes validation. When that report calls a non-zero
+test-suite exit an "expected pre-existing failure" (or baseline / known
+failure) it must carry pre-merge proof; otherwise the closure buries an
+unproven regression as an accepted baseline and weakens controller
+confidence in the durable state.
+
+This module fails closed on exactly that case by reusing the pre-merge
+baseline proof verifier (#533). A closure report is allowed when it is
+empty (no validation claim), a clean pass, or a baseline failure proven on
+the PR pre-merge base commit (or a documented known-failure record that
+predates the PR).
+"""
+
+from __future__ import annotations
+
+from typing import Any
+
+from premerge_baseline_proof import CLEAN_PASS, assess_premerge_baseline_proof
+
+
+def assess_controller_closure_baseline_proof(
+    closure_report: str | None,
+) -> dict[str, Any]:
+    """Assess whether an issue-closure report may proceed.
+
+    Returns a dict with ``block``, ``proven``, ``label``, ``reasons``,
+    ``skipped`` and ``safe_next_action``. Only blocks when the closure
+    report claims a non-zero validation exit is an expected
+    pre-existing/baseline failure without valid pre-merge proof.
+    """
+    text = (closure_report or "").strip()
+    if not text:
+        return {
+            "block": False,
+            "proven": True,
+            "label": CLEAN_PASS,
+            "reasons": [],
+            "skipped": True,
+            "safe_next_action": "",
+        }
+
+    result = assess_premerge_baseline_proof(text)
+    block = bool(result.get("block"))
+    return {
+        "block": block,
+        "proven": not block,
+        "label": result.get("label"),
+        "reasons": list(result.get("reasons") or []),
+        "skipped": bool(result.get("skipped", False)),
+        "safe_next_action": (
+            result.get("safe_next_action")
+            or (
+                "provide pre-merge baseline proof (base commit, tested commit, "
+                "command, exit status, failure signature) before closing on an "
+                "expected pre-existing failure"
+            )
+        )
+        if block
+        else "",
+    }