fix(observability): merge-gate on deploy, full token input, Plane Done, artifact links

1. BUG 8 (second door): merge webhook no longer fake-completes a task at the
   deploy stage; done is gated by the deployer verdict (check_deploy_status).
   Other stages keep merge->done.
2. Token accounting: parse+persist cache_creation_input_tokens (new
   idempotent agent_runs column). usage_comment / task_summary now show the
   FULL input (input + cache_read + cache_creation) with a cached breakdown.
   cost_usd untouched.
3. deploy->done success now forces the Plane issue to terminal Done state.
4. All agents (architect/developer/reviewer/tester/deployer) attach artifact
   links to their finish comment via gitea_public_url.

Tests added for each fix; pytest 244 passed / 9 failed (off-limits HMAC group).

tests/test_webhooks.py

@@ -433,3 +433,67 @@ def test_ci_failure_development_escalates_at_limit(
     assert "after CI failure" in err_msg
     # Stage untouched.
     assert not mock_update_stage.called
+
+
+# ---------------------------------------------------------------------------
+# BUG 8 (second door): a merged-PR webhook must NOT fake-complete a task that is
+# still in the deploy stage. On `deploy` done is gated by the deployer's verdict
+# (check_deploy_status via advance_stage), not by the merge event. For every
+# other stage the merge->done behaviour is preserved. Pure-logic tests: invoke
+# handle_pr() directly with mocked helpers (no HMAC barrier).
+# ---------------------------------------------------------------------------
+
+def _merged_pr_payload(branch="feature/ET-012-x"):
+    return {
+        "action": "closed",
+        "pull_request": {
+            "merged": True,
+            "number": 7,
+            "head": {"ref": branch},
+        },
+        "repository": {"name": "enduro-trails"},
+    }
+
+
+@patch("src.webhooks.gitea.notify_stage_change")
+@patch("src.webhooks.gitea.update_task_stage")
+@patch("src.webhooks.gitea.get_task_by_repo_branch")
+@patch("src.webhooks.gitea.get_project_by_repo")
+def test_merge_on_deploy_stage_does_not_set_done(
+    mock_proj, mock_task, mock_update_stage, mock_notify,
+):
+    """FIX 1: merge at deploy stage is ignored — done is gated by deployer verdict."""
+    from src.webhooks.gitea import handle_pr
+
+    mock_proj.return_value = {"repo": "enduro-trails"}
+    mock_task.return_value = {
+        "id": 1, "stage": "deploy", "work_item_id": "ET-012",
+    }
+
+    asyncio.run(handle_pr(_merged_pr_payload()))
+
+    # The merge-driven done path must NOT run on deploy.
+    assert not mock_update_stage.called
+    assert not mock_notify.called
+
+
+@patch("src.webhooks.gitea.notify_stage_change")
+@patch("src.webhooks.gitea.update_task_stage")
+@patch("src.webhooks.gitea.get_task_by_repo_branch")
+@patch("src.webhooks.gitea.get_project_by_repo")
+def test_merge_on_non_deploy_stage_sets_done(
+    mock_proj, mock_task, mock_update_stage, mock_notify,
+):
+    """FIX 1: merge behaviour is preserved for non-deploy stages (e.g. review)."""
+    from src.webhooks.gitea import handle_pr
+
+    mock_proj.return_value = {"repo": "enduro-trails"}
+    mock_task.return_value = {
+        "id": 2, "stage": "review", "work_item_id": "ET-013",
+    }
+
+    asyncio.run(handle_pr(_merged_pr_payload(branch="feature/ET-013-x")))
+
+    # Non-deploy stages still get the merge-driven done.
+    mock_update_stage.assert_called_once_with(2, "done")
+    assert mock_notify.called