fix: surface skipped tracker cleanup on merge read-back failure (#98)

gitea_merge_pr ran cleanup_in_progress_for_pr inside the same try as the
post-merge read-back GET; a read-back failure silently skipped tracker
cleanup, leaving only merge_commit=null and no cleanup_status at all, so
status:in-progress could stay stuck while the merge read as full success.

Split the block: read-back failure now returns an explicit
cleanup_status='skipped (merge read-back failed)', and an unexpected
cleanup exception returns 'skipped (cleanup error: <redacted>)' instead of
masking merge_commit. Cleanup still never blocks a performed merge, the
happy-path API call sequence is unchanged, and _redact keeps credentials
out of surfaced errors.

Add regression tests: read-back failure => merge still performed, explicit
skip status, no tracker DELETE traffic; cleanup exception => surfaced and
redacted.

Fixes #98.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

mcp_server.py

@@ -1098,16 +1098,30 @@ def gitea_merge_pr(
             payload["MergeMessageField"] = message
         api_request("POST", merge_url, auth, payload)
         # Best-effort read-back of the merge commit SHA (redacted on error).
+        merged = None
         try:
             merged = api_request(
                 "GET", f"{repo_api_url(h, o, r)}/pulls/{pr_number}", auth
             )
             result["merge_commit"] = (merged or {}).get("merged_commit_sha")
-
-            cleanup = cleanup_in_progress_for_pr(merged or {}, remote, host, org, repo)
-            result["cleanup_status"] = cleanup.get("cleanup_status")
         except Exception:
             result["merge_commit"] = None
+
+        # Tracker cleanup (#98): never blocks the merge, and always surfaces an
+        # explicit cleanup_status once the merge mutation has happened. Cleanup
+        # needs the PR title/body/branch, which only the read-back payload
+        # carries here — so a failed read-back is an explicit skip, not a
+        # silent one.
+        if merged is None:
+            result["cleanup_status"] = "skipped (merge read-back failed)"
+        else:
+            try:
+                cleanup = cleanup_in_progress_for_pr(merged, remote, host, org, repo)
+                result["cleanup_status"] = cleanup.get("cleanup_status")
+            except Exception as cleanup_exc:  # noqa: BLE001 — redact before surfacing
+                result["cleanup_status"] = (
+                    f"skipped (cleanup error: {_redact(str(cleanup_exc))})"
+                )
     except Exception as exc:  # noqa: BLE001 — redact before surfacing
         reasons.append(f"merge failed: {_redact(str(exc))}")
         return result