feat(webui): read-only system-health API (Closes #634)

Adds `GET /api/v1/system/health`, a structured read-only health surface for
automated readiness checks, and keeps `/health` as the cheap liveness probe.

webui/system_health.py composes a DTO from fail-soft dependency probes: the
control-plane database, the local checkout, and — opt-in via `?deep=1` — live
Gitea reachability, each carrying status, reason, and probe latency. Required
probes drive readiness; the optional Gitea probe can only degrade overall
status, because local inventory stays serveable when the remote is
unreachable. A probe that did not run leaves readiness incomplete rather than
silently passing.

Read-only throughout: the control-plane database is opened through a `mode=ro`
URI because `ControlPlaneDB.__init__` creates directories and runs migrations,
which a health check must never do. No restart or reload control is exposed;
those are Phase 2 and #630 forbids process-kill recovery.

No unproven claims: `stale_runtime.mutation_safe` is true only when the
runtime, checkout, and remote commits are all known and equal, and MCP
namespaces always report `unproven` because a web process cannot exercise the
IDE-managed client path (#543). Probe details are redacted at the browser
boundary — URLs lose userinfo and query strings, credential-shaped text is
masked.

`/health` is expanded additively: every MVP key is retained, plus `started_at`,
`uptime_seconds`, and a pointer to the versioned API. The versioned route
returns 503 when not ready so automation can branch on the status code alone.

Verified at master 9eb0f29: focused file 40 passed / 11 subtests; `-k "webui or
health"` 230 passed / 159 subtests; full suite 4358 passed with the 11
pre-existing master-drift failures unchanged from the clean-master baseline.

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

docs/webui-local-dev.md

@@ -48,7 +48,8 @@ that govern when a write path may open (#632, epic #631).
 | Path | Description |
 |------|-------------|
 | `/` | Home / operator overview |
-| `/health` | JSON liveness (`status`, `service`, `mode`, `timestamp`) |
+| `/health` | JSON liveness (`status`, `service`, `mode`, `timestamp`, `uptime_seconds`) |
+| `/api/v1/system/health` | Structured read-only system health (#634) |
 | `/queue` | Live PR and issue queue dashboard (#429) |
 | `/api/queue` | JSON queue export with pagination metadata |
 | `/projects` | Project registry list (#427) |
@@ -72,6 +73,85 @@ Most routes are GET-only. POST/PUT/PATCH/DELETE return `405` with
 `read-only-mvp`, except `/audit` and `/api/audit` which accept POST for
 local validator preview only (no Gitea mutations, no server-side storage).
 
+## System health API (#634)
+
+`GET /api/v1/system/health` is the structured, read-only health surface for
+automated readiness checks. It is the first console API under the `/api/v1`
+prefix; the unversioned MVP exports remain as compatibility aliases.
+
+`/health` is unchanged for existing consumers — every MVP key is still present
+— and now also carries `started_at`, `uptime_seconds`, and a
+`system_health_api` pointer. It stays deliberately cheap and runs no dependency
+probe, because answering readiness costs real work.
+
+**Status codes.** `200` when ready, `503` when a required dependency failed or
+was never probed. Automation can branch on the code without parsing the body.
+
+**Query flags.** The Gitea check is a network call, so it is opt-in:
+`GET /api/v1/system/health?deep=1` runs it and caches the result for
+`WEBUI_HEALTH_PROBE_TTL_SECONDS` (default 15s) so dashboard polling does not
+amplify into remote load. Without the flag that probe reports `skipped`.
+
+**Dependencies.** `control_plane_db` and `repository` are required and drive
+readiness. `gitea` is optional: when it fails the overall `status` degrades but
+`readiness.ready` stays true, because local inventory is still serveable. Each
+entry carries `status`, `detail`, `required`, and `latency_ms`.
+
+Two honesty rules are worth knowing before reading the payload:
+
+* `stale_runtime.mutation_safe` is true only when the runtime, checkout, and
+  remote-tracking commits are all known and equal. An unfetched remote is
+  reported as indeterminate, never as safe.
+* `mcp_namespaces` entries are always `unproven`. A web process runs outside
+  the IDE-managed MCP client and cannot invoke a namespace tool, so per #543
+  only a `client_namespace` probe can prove that path.
+
+Sample response (abridged, healthy):
+
+```json
+{
+  "status": "ok",
+  "service": "mcp-control-plane-webui",
+  "mode": "read-only",
+  "api": "/api/v1/system/health",
+  "timestamp": "2026-07-22T11:04:18.512034+00:00",
+  "readiness": { "ready": true, "complete": true, "reasons": [] },
+  "version": {
+    "git_sha": "620ed6e9a9550b8da2ceb82d9ab8744e8920490f",
+    "git_describe": "v1.1.0-898-g620ed6e",
+    "control_plane_schema_version": 4,
+    "python_version": "3.14.5",
+    "known": true
+  },
+  "process": { "started_at": "2026-07-22T10:58:02.114+00:00", "uptime_seconds": 376.4 },
+  "deep_probes_requested": false,
+  "dependencies": [
+    {
+      "name": "control_plane_db",
+      "kind": "sqlite",
+      "status": "ok",
+      "detail": "schema v4 readable",
+      "required": true,
+      "healthy": true,
+      "latency_ms": 1.482,
+      "metadata": { "schema_version": 4, "active_leases": 3 }
+    },
+    { "name": "repository", "kind": "git", "status": "ok", "required": true, "healthy": true },
+    { "name": "gitea", "kind": "http", "status": "skipped", "required": false, "healthy": false }
+  ],
+  "mcp_namespaces": [
+    { "namespace": "gitea-author", "required_tool": "gitea_whoami", "status": "unproven" }
+  ],
+  "stale_runtime": { "stale": false, "determinable": true, "mutation_safe": true, "reasons": [] },
+  "probe_errors": []
+}
+```
+
+No restart, reload, or process-kill control is exposed here: those are Phase 2
+at the earliest, and #630 forbids process-kill recovery outright. Every probe
+opens its subject read-only — the control-plane database is opened through a
+`mode=ro` URI so a health check can never create or migrate a schema.
+
 ## Report audit (#431)
 
 Paste an LLM final report at `/audit` or POST JSON to `/api/audit`. The UI

tests/test_webui_system_health.py

@@ -0,0 +1,499 @@
+"""Tests for the read-only system-health API (#634).
+
+Covers the acceptance criteria directly: a structured payload with readiness
+and a dependency list (AC1), version and uptime when knowable (AC2), stale
+runtime reported without a false mutation-safe claim (AC3), and the healthy /
+degraded-dependency / redaction cases (AC4).
+"""
+import json
+import os
+import sqlite3
+import sys
+import tempfile
+import unittest
+from pathlib import Path
+from unittest import mock
+
+sys.path.insert(0, str(Path(__file__).resolve().parent.parent))
+
+from starlette.testclient import TestClient
+
+import control_plane_db
+from webui.app import create_app
+from webui.deployment_boundary import scan_text_for_client_secrets
+from webui.system_health import (
+    API_PATH,
+    STATUS_DEGRADED,
+    STATUS_DOWN,
+    STATUS_OK,
+    STATUS_SKIPPED,
+    DependencyProbe,
+    StaleRuntime,
+    assess_stale_runtime,
+    clear_probe_cache,
+    load_system_health,
+    namespace_summaries,
+    probe_control_plane_db,
+    probe_gitea,
+    process_uptime,
+    redact,
+    redact_url,
+    snapshot_to_dict,
+)
+
+
+def _probe(name, status, *, required=True, detail="detail", kind="test"):
+    return DependencyProbe(
+        name=name,
+        kind=kind,
+        status=status,
+        detail=detail,
+        required=required,
+        latency_ms=1.5,
+        metadata={},
+    )
+
+
+_ALL_HEALTHY = (
+    _probe("control_plane_db", STATUS_OK, kind="sqlite"),
+    _probe("repository", STATUS_OK, kind="git"),
+    _probe("gitea", STATUS_OK, required=False, kind="http"),
+)
+
+_CLEAN_PARITY = StaleRuntime(
+    daemon_head="abc123",
+    checkout_head="abc123",
+    remote_head="abc123",
+    stale=False,
+    determinable=True,
+    mutation_safe=True,
+    reasons=(),
+)
+
+
+class CleanParityMixin:
+    """Pin parity for tests about aggregation rather than staleness.
+
+    Without this the assertions depend on the real checkout: a worktree whose
+    branch is ahead of its upstream is genuinely stale, which would degrade the
+    overall status and make these cases fail for an unrelated reason.
+    """
+
+    def setUp(self):
+        super().setUp()
+        patcher = mock.patch(
+            "webui.system_health.assess_stale_runtime",
+            return_value=_CLEAN_PARITY,
+        )
+        patcher.start()
+        self.addCleanup(patcher.stop)
+
+
+class TestDependencyAggregation(CleanParityMixin, unittest.TestCase):
+    """AC1 — readiness and dependency list derived from probe results."""
+
+    def test_all_healthy_is_ok_and_ready(self):
+        snapshot = load_system_health(probes=_ALL_HEALTHY, daemon_head="abc123")
+        self.assertEqual(snapshot.status, STATUS_OK)
+        self.assertTrue(snapshot.ready)
+        self.assertTrue(snapshot.readiness_complete)
+        self.assertEqual(snapshot.readiness_reasons, ())
+        self.assertEqual(len(snapshot.dependencies), 3)
+
+    def test_required_dependency_down_blocks_readiness(self):
+        probes = (
+            _probe("control_plane_db", STATUS_DOWN, detail="file missing", kind="sqlite"),
+            _probe("repository", STATUS_OK, kind="git"),
+            _probe("gitea", STATUS_OK, required=False, kind="http"),
+        )
+        snapshot = load_system_health(probes=probes, daemon_head="abc123")
+        self.assertEqual(snapshot.status, STATUS_DOWN)
+        self.assertFalse(snapshot.ready)
+        self.assertTrue(
+            any("control_plane_db" in reason for reason in snapshot.readiness_reasons)
+        )
+
+    def test_optional_dependency_down_degrades_but_stays_ready(self):
+        """A failing optional probe must not claim the process itself is unready."""
+        probes = (
+            _probe("control_plane_db", STATUS_OK, kind="sqlite"),
+            _probe("repository", STATUS_OK, kind="git"),
+            _probe("gitea", STATUS_DOWN, required=False, detail="timeout", kind="http"),
+        )
+        snapshot = load_system_health(probes=probes, daemon_head="abc123")
+        self.assertEqual(snapshot.status, STATUS_DEGRADED)
+        self.assertTrue(snapshot.ready)
+        self.assertTrue(any("gitea" in reason for reason in snapshot.readiness_reasons))
+
+    def test_unrun_required_probe_leaves_readiness_incomplete(self):
+        """Not probed is not the same as passing."""
+        probes = (
+            _probe("control_plane_db", STATUS_OK, kind="sqlite"),
+            _probe("repository", STATUS_SKIPPED, detail="offline", kind="git"),
+        )
+        snapshot = load_system_health(probes=probes, daemon_head="abc123")
+        self.assertFalse(snapshot.ready)
+        self.assertFalse(snapshot.readiness_complete)
+        self.assertEqual(snapshot.status, STATUS_DEGRADED)
+
+    def test_skipped_optional_probe_does_not_block_readiness(self):
+        probes = (
+            _probe("control_plane_db", STATUS_OK, kind="sqlite"),
+            _probe("repository", STATUS_OK, kind="git"),
+            _probe("gitea", STATUS_SKIPPED, required=False, kind="http"),
+        )
+        snapshot = load_system_health(probes=probes, daemon_head="abc123")
+        self.assertTrue(snapshot.ready)
+        self.assertTrue(snapshot.readiness_complete)
+
+
+class TestVersionAndUptime(CleanParityMixin, unittest.TestCase):
+    """AC2 — version and uptime present when knowable."""
+
+    def test_uptime_and_start_time_present(self):
+        snapshot = load_system_health(probes=_ALL_HEALTHY, daemon_head="abc123")
+        self.assertGreaterEqual(snapshot.uptime_seconds, 0.0)
+        self.assertIn("T", snapshot.started_at)
+
+    def test_process_uptime_helper_matches_shape(self):
+        started_at, uptime = process_uptime()
+        self.assertIn("T", started_at)
+        self.assertGreaterEqual(uptime, 0.0)
+
+    def test_version_reports_python_and_schema_version(self):
+        probes = (
+            DependencyProbe(
+                name="control_plane_db",
+                kind="sqlite",
+                status=STATUS_OK,
+                detail="ok",
+                required=True,
+                latency_ms=1.0,
+                metadata={"schema_version": control_plane_db.SCHEMA_VERSION},
+            ),
+            _probe("repository", STATUS_OK, kind="git"),
+        )
+        snapshot = load_system_health(probes=probes, daemon_head="abc123")
+        self.assertEqual(
+            snapshot.version.control_plane_schema_version,
+            control_plane_db.SCHEMA_VERSION,
+        )
+        self.assertTrue(snapshot.version.python_version)
+
+    def test_version_known_flag_false_when_sha_unavailable(self):
+        with mock.patch("webui.system_health._git", return_value=None):
+            snapshot = load_system_health(probes=_ALL_HEALTHY, daemon_head="abc")
+        self.assertIsNone(snapshot.version.git_sha)
+        self.assertFalse(snapshot.version.known)
+
+
+class TestStaleRuntime(unittest.TestCase):
+    """AC3 — stale runtime reflected without a false mutation-safe claim."""
+
+    def test_matching_commits_are_mutation_safe(self):
+        assessment = assess_stale_runtime(
+            Path("/tmp"),
+            daemon_head="aaa",
+            git_reader=lambda *args: "aaa",
+        )
+        self.assertFalse(assessment.stale)
+        self.assertTrue(assessment.determinable)
+        self.assertTrue(assessment.mutation_safe)
+
+    def test_diverged_commits_are_stale_and_not_mutation_safe(self):
+        reads = {"HEAD": "aaa", "@{upstream}": "bbb"}
+        assessment = assess_stale_runtime(
+            Path("/tmp"),
+            daemon_head="aaa",
+            git_reader=lambda *args: reads.get(args[-1]),
+        )
+        self.assertTrue(assessment.stale)
+        self.assertFalse(assessment.mutation_safe)
+        self.assertTrue(assessment.reasons)
+
+    def test_unknown_remote_is_not_mutation_safe(self):
+        """Indeterminate must never read as safe."""
+        reads = {"HEAD": "aaa", "@{upstream}": None}
+        assessment = assess_stale_runtime(
+            Path("/tmp"),
+            daemon_head="aaa",
+            git_reader=lambda *args: reads.get(args[-1]),
+        )
+        self.assertFalse(assessment.determinable)
+        self.assertFalse(assessment.mutation_safe)
+        self.assertFalse(assessment.stale)
+        self.assertTrue(
+            any("indeterminate" in reason for reason in assessment.reasons)
+        )
+
+    def test_unobservable_daemon_head_is_disclosed(self):
+        assessment = assess_stale_runtime(
+            Path("/tmp"),
+            git_reader=lambda *args: "aaa",
+        )
+        self.assertTrue(
+            any("not observable" in reason for reason in assessment.reasons)
+        )
+
+    def test_stale_runtime_degrades_overall_status(self):
+        reads = {"HEAD": "aaa", "@{upstream}": "bbb"}
+        # Pinned rather than inherited: this path uses the default git reader,
+        # so the assertion must hold whether or not the suite runs offline.
+        with mock.patch.dict(os.environ, {"WEBUI_TEST_OFFLINE": ""}), mock.patch(
+            "webui.system_health._git",
+            side_effect=lambda repo, *args: reads.get(args[-1]),
+        ):
+            snapshot = load_system_health(probes=_ALL_HEALTHY, daemon_head="aaa")
+        self.assertTrue(snapshot.stale_runtime.stale)
+        self.assertFalse(snapshot.stale_runtime.mutation_safe)
+        self.assertEqual(snapshot.status, STATUS_DEGRADED)
+
+
+class TestControlPlaneDbProbe(unittest.TestCase):
+    """The required local dependency, probed read-only."""
+
+    def setUp(self):
+        self.tmp = tempfile.TemporaryDirectory()
+        self.addCleanup(self.tmp.cleanup)
+        self.db_path = str(Path(self.tmp.name) / "control-plane.db")
+
+    def _build_db(self, schema_version):
+        conn = sqlite3.connect(self.db_path)
+        conn.execute("CREATE TABLE schema_meta (key TEXT PRIMARY KEY, value TEXT)")
+        conn.execute("CREATE TABLE leases (lease_id TEXT PRIMARY KEY, status TEXT)")
+        conn.execute(
+            "INSERT INTO schema_meta(key, value) VALUES ('schema_version', ?)",
+            (str(schema_version),),
+        )
+        conn.execute("INSERT INTO leases(lease_id, status) VALUES ('l1', 'active')")
+        conn.commit()
+        conn.close()
+
+    def test_missing_database_is_down(self):
+        probe = probe_control_plane_db(str(Path(self.tmp.name) / "absent.db"))
+        self.assertEqual(probe.status, STATUS_DOWN)
+        self.assertTrue(probe.required)
+        self.assertIsNotNone(probe.latency_ms)
+
+    def test_matching_schema_is_ok(self):
+        self._build_db(control_plane_db.SCHEMA_VERSION)
+        probe = probe_control_plane_db(self.db_path)
+        self.assertEqual(probe.status, STATUS_OK)
+        self.assertEqual(
+            probe.metadata["schema_version"], control_plane_db.SCHEMA_VERSION
+        )
+        self.assertEqual(probe.metadata["active_leases"], 1)
+
+    def test_mismatched_schema_is_degraded(self):
+        self._build_db(control_plane_db.SCHEMA_VERSION + 99)
+        probe = probe_control_plane_db(self.db_path)
+        self.assertEqual(probe.status, STATUS_DEGRADED)
+
+    def test_probe_does_not_create_a_database(self):
+        """A health check must never initialise the substrate it inspects."""
+        absent = str(Path(self.tmp.name) / "never-created.db")
+        probe_control_plane_db(absent)
+        self.assertFalse(Path(absent).exists())
+
+    def test_unreadable_database_is_down_not_raised(self):
+        Path(self.db_path).write_text("this is not a sqlite database")
+        probe = probe_control_plane_db(self.db_path)
+        self.assertEqual(probe.status, STATUS_DOWN)
+
+
+class TestRedaction(unittest.TestCase):
+    """AC4 — redaction. No credential-shaped text crosses the boundary."""
+
+    def test_redacts_token_assignment(self):
+        cleaned = redact("failed with token=ghp_ABCDEFGHIJKLMNOPQRSTUVWXYZ012345")
+        self.assertNotIn("ghp_ABCDEFGHIJKLMNOPQRSTUVWXYZ012345", cleaned)
+        self.assertIn("[redacted]", cleaned)
+
+    def test_redacts_authorization_header_text(self):
+        cleaned = redact("Authorization: Bearer abcdefghijklmnopqrstuvwxyz123456")
+        self.assertNotIn("abcdefghijklmnopqrstuvwxyz123456", cleaned)
+
+    def test_redacts_long_opaque_strings(self):
+        cleaned = redact("value 0123456789abcdef0123456789abcdef here")
+        self.assertNotIn("0123456789abcdef0123456789abcdef", cleaned)
+
+    def test_url_userinfo_and_query_are_stripped(self):
+        cleaned = redact_url("https://user:[email protected]/api/v1?token=xyz")
+        self.assertNotIn("secretpass", cleaned)
+        self.assertNotIn("token=xyz", cleaned)
+        self.assertEqual(cleaned, "https://gitea.example.com/api/v1")
+
+    def test_url_inside_free_text_is_redacted(self):
+        cleaned = redact("GET https://u:[email protected]/x?token=abc failed")
+        self.assertNotIn("u:p@", cleaned)
+        self.assertNotIn("token=abc", cleaned)
+
+    def test_gitea_probe_failure_detail_is_redacted(self):
+        boom = RuntimeError(
+            "connection refused for https://user:[email protected]/api/v1/version"
+        )
+        with mock.patch("webui.system_health.get_auth_header", return_value="token x"), \
+                mock.patch("webui.system_health.api_request", side_effect=boom):
+            probe = probe_gitea("gitea.example.com")
+        self.assertEqual(probe.status, STATUS_DOWN)
+        self.assertNotIn("hunter2", probe.detail)
+        self.assertEqual(scan_text_for_client_secrets(probe.detail), [])
+
+    def test_credential_guard_refusal_is_a_status_not_a_crash(self):
+        with mock.patch(
+            "webui.system_health.get_auth_header",
+            side_effect=RuntimeError("daemon guard refused"),
+        ):
+            probe = probe_gitea("gitea.example.com")
+        self.assertEqual(probe.status, STATUS_DEGRADED)
+        self.assertFalse(probe.required)
+
+
+class TestNamespaceSummaries(unittest.TestCase):
+    """A web process cannot prove IDE namespace health, and must not claim to."""
+
+    def test_every_namespace_reports_unproven(self):
+        rows = namespace_summaries()
+        self.assertTrue(rows)
+        for row in rows:
+            with self.subTest(namespace=row["namespace"]):
+                self.assertEqual(row["status"], "unproven")
+                self.assertFalse(row["ide_namespace_proven"])
+                self.assertIn("client_namespace", row["reason"])
+
+
+class TestSystemHealthRoutes(CleanParityMixin, unittest.TestCase):
+    """The HTTP surface: versioned path, status codes, read-only guard."""
+
+    def setUp(self):
+        super().setUp()
+        clear_probe_cache()
+        self.addCleanup(clear_probe_cache)
+        self.client = TestClient(create_app())
+
+    def _patch_snapshot(self, probes, daemon_head="abc123"):
+        snapshot = load_system_health(probes=probes, daemon_head=daemon_head)
+        patcher = mock.patch(
+            "webui.app.load_system_health",
+            return_value=snapshot,
+        )
+        patcher.start()
+        self.addCleanup(patcher.stop)
+        return snapshot
+
+    def test_versioned_route_is_registered(self):
+        self.assertEqual(API_PATH, "/api/v1/system/health")
+        self._patch_snapshot(_ALL_HEALTHY)
+        response = self.client.get(API_PATH)
+        self.assertEqual(response.status_code, 200)
+
+    def test_healthy_payload_shape(self):
+        self._patch_snapshot(_ALL_HEALTHY)
+        data = self.client.get(API_PATH).json()
+        self.assertEqual(data["status"], STATUS_OK)
+        self.assertTrue(data["readiness"]["ready"])
+        self.assertTrue(data["readiness"]["complete"])
+        self.assertEqual(data["api"], API_PATH)
+        self.assertEqual(len(data["dependencies"]), 3)
+        for key in ("version", "process", "stale_runtime", "mcp_namespaces"):
+            self.assertIn(key, data)
+        self.assertIn("uptime_seconds", data["process"])
+        self.assertIn("mutation_safe", data["stale_runtime"])
+
+    def test_degraded_dependency_returns_503(self):
+        probes = (
+            _probe("control_plane_db", STATUS_DOWN, detail="missing", kind="sqlite"),
+            _probe("repository", STATUS_OK, kind="git"),
+        )
+        self._patch_snapshot(probes)
+        response = self.client.get(API_PATH)
+        self.assertEqual(response.status_code, 503)
+        data = response.json()
+        self.assertFalse(data["readiness"]["ready"])
+        self.assertTrue(data["readiness"]["reasons"])
+
+    def test_dependency_entries_expose_status_and_latency(self):
+        self._patch_snapshot(_ALL_HEALTHY)
+        data = self.client.get(API_PATH).json()
+        names = {entry["name"] for entry in data["dependencies"]}
+        self.assertEqual(names, {"control_plane_db", "repository", "gitea"})
+        for entry in data["dependencies"]:
+            with self.subTest(dependency=entry["name"]):
+                self.assertIn("status", entry)
+                self.assertIn("required", entry)
+                self.assertIn("latency_ms", entry)
+
+    def test_response_body_carries_no_client_secrets(self):
+        self._patch_snapshot(_ALL_HEALTHY)
+        body = self.client.get(API_PATH).text
+        self.assertEqual(scan_text_for_client_secrets(body), [])
+
+    def test_deep_flag_is_forwarded(self):
+        snapshot = load_system_health(probes=_ALL_HEALTHY, daemon_head="abc")
+        with mock.patch(
+            "webui.app.load_system_health", return_value=snapshot
+        ) as loader:
+            self.client.get(f"{API_PATH}?deep=1")
+            loader.assert_called_once_with(deep=True)
+
+    def test_shallow_is_the_default(self):
+        snapshot = load_system_health(probes=_ALL_HEALTHY, daemon_head="abc")
+        with mock.patch(
+            "webui.app.load_system_health", return_value=snapshot
+        ) as loader:
+            self.client.get(API_PATH)
+            loader.assert_called_once_with(deep=False)
+
+    def test_route_rejects_mutation_methods(self):
+        for method in ("POST", "PUT", "PATCH", "DELETE"):
+            with self.subTest(method=method):
+                response = self.client.request(method, API_PATH)
+                self.assertEqual(response.status_code, 405)
+                self.assertEqual(response.json()["error"], "read-only-mvp")
+
+    def test_default_shallow_call_skips_the_network_probe(self):
+        """The expensive probe must not run unless it was asked for."""
+        with mock.patch("webui.system_health.probe_gitea") as probe:
+            snapshot = load_system_health(deep=False)
+        probe.assert_not_called()
+        gitea = next(p for p in snapshot.dependencies if p.name == "gitea")
+        self.assertEqual(gitea.status, STATUS_SKIPPED)
+
+
+class TestHealthRouteBackwardCompatibility(unittest.TestCase):
+    """`/health` is expanded additively; MVP consumers must keep working."""
+
+    def setUp(self):
+        self.client = TestClient(create_app())
+
+    def test_mvp_keys_are_unchanged(self):
+        data = self.client.get("/health").json()
+        self.assertEqual(data["status"], "ok")
+        self.assertEqual(data["service"], "mcp-control-plane-webui")
+        self.assertEqual(data["mode"], "read-only-mvp")
+        self.assertIn("timestamp", data)
+        self.assertEqual(data["deployment"]["mode"], "internal-operator-console")
+
+    def test_health_points_at_the_versioned_api(self):
+        data = self.client.get("/health").json()
+        self.assertEqual(data["system_health_api"], API_PATH)
+        self.assertIn("uptime_seconds", data)
+        self.assertIn("started_at", data)
+
+    def test_health_runs_no_dependency_probe(self):
+        """Liveness must stay cheap: no probe, no snapshot assembly."""
+        with mock.patch("webui.app.load_system_health") as loader:
+            response = self.client.get("/health")
+        self.assertEqual(response.status_code, 200)
+        loader.assert_not_called()
+
+
+class TestSnapshotSerialisation(CleanParityMixin, unittest.TestCase):
+    def test_snapshot_dict_is_json_serialisable(self):
+        snapshot = load_system_health(probes=_ALL_HEALTHY, daemon_head="abc123")
+        encoded = json.dumps(snapshot_to_dict(snapshot))
+        self.assertIn("readiness", encoded)
+
+
+if __name__ == "__main__":
+    unittest.main()

webui/app.py

@@ -29,6 +29,12 @@ from webui.worktree_scanner import load_hygiene_snapshot, snapshot_to_dict as wo
 from webui.worktree_views import render_worktrees_page
 from webui.runtime_health import load_runtime_snapshot, snapshot_to_dict as runtime_snapshot_to_dict
 from webui.runtime_views import render_runtime_page
+from webui.system_health import (
+    API_PATH as SYSTEM_HEALTH_API_PATH,
+    load_system_health,
+    process_uptime,
+    snapshot_to_dict as system_health_to_dict,
+)
 
 _READ_ONLY_METHODS = frozenset({"GET", "HEAD", "OPTIONS"})
 _AUDIT_MUTATION_PATHS = frozenset({"/audit", "/api/audit"})
@@ -62,16 +68,43 @@ async def home(_request: Request) -> HTMLResponse:
 
 
 async def health(_request: Request) -> JSONResponse:
+    """Liveness only — deliberately cheap, runs no dependency probe (#634).
+
+    Every MVP key is retained so existing pollers keep working; the additions
+    are a pointer to the structured API and the in-memory process uptime.
+    Readiness lives at that API because answering it costs real probes.
+    """
     bind_host = _request.app.state.webui_bind_host
+    started_at, uptime_seconds = process_uptime()
     return JSONResponse({
         "status": "ok",
         "service": "mcp-control-plane-webui",
         "mode": "read-only-mvp",
         "timestamp": datetime.now(timezone.utc).isoformat(),
         "deployment": deployment_snapshot(bind_host=bind_host),
+        "started_at": started_at,
+        "uptime_seconds": uptime_seconds,
+        "system_health_api": SYSTEM_HEALTH_API_PATH,
     })
 
 
+def _truthy_flag(value: str | None) -> bool:
+    return (value or "").strip().lower() in {"1", "true", "yes", "on"}
+
+
+async def api_system_health(request: Request) -> JSONResponse:
+    """Structured read-only system health (#634).
+
+    `?deep=1` opts into the expensive network probe. The response status code
+    reflects readiness so automated checks can branch on it without parsing the
+    body: 200 when ready, 503 when a required dependency failed or never ran.
+    """
+    deep = _truthy_flag(request.query_params.get("deep"))
+    snapshot = load_system_health(deep=deep)
+    payload = system_health_to_dict(snapshot)
+    return JSONResponse(payload, status_code=200 if snapshot.ready else 503)
+
+
 async def queue(_request: Request) -> HTMLResponse:
     snapshot = load_queue_snapshot()
     return HTMLResponse(render_page(title="Queue", body_html=render_queue_page(snapshot)))
@@ -263,6 +296,7 @@ def create_app(*, bind_host: str | None = None) -> Starlette:
         routes=[
             Route("/", home, methods=["GET"]),
             Route("/health", health, methods=["GET"]),
+            Route(SYSTEM_HEALTH_API_PATH, api_system_health, methods=["GET"]),
             Route("/queue", queue, methods=["GET"]),
             Route("/api/queue", api_queue, methods=["GET"]),
             Route("/projects", projects, methods=["GET"]),

webui/system_health.py

@@ -0,0 +1,682 @@
+"""Read-only system-health model for the operator console API (#634).
+
+`/health` answers liveness only. Operators automating readiness checks need a
+structured view of *why* the control plane is or is not usable: which
+dependencies answered, how long they took, what version of the code is running,
+and whether the runtime is stale relative to its remote.
+
+Three rules shape this module.
+
+* **Read-only.** Every probe opens its subject read-only. The control-plane
+  database is opened through a ``mode=ro`` URI so a health check can never
+  create or migrate a schema, and no probe writes, restarts, or reloads
+  anything — restart controls are Phase 2, and #630 forbids process-kill
+  recovery outright.
+* **Fail-soft.** A dependency that is unreachable is a *status*, not an
+  exception. Probes catch their own failures and report them as a degraded or
+  down entry carrying a reason.
+* **Never claim more than was proven.** Readiness is derived only from probes
+  that actually ran, ``mutation_safe`` stays false unless the parity commits are
+  known and equal, and an MCP namespace is reported unproven because a web
+  process cannot exercise the IDE-managed client path (#543).
+"""
+
+from __future__ import annotations
+
+import os
+import re
+import sqlite3
+import subprocess
+import time
+from dataclasses import dataclass
+from datetime import datetime, timezone
+from pathlib import Path
+from typing import Any, Callable
+from urllib.parse import urlsplit, urlunsplit
+
+import control_plane_db
+import mcp_namespace_health
+from gitea_auth import api_request, get_auth_header, gitea_url
+
+from webui.project_registry import load_registry
+
+SERVICE_NAME = "mcp-control-plane-webui"
+API_PATH = "/api/v1/system/health"
+
+STATUS_OK = "ok"
+STATUS_DEGRADED = "degraded"
+STATUS_DOWN = "down"
+STATUS_SKIPPED = "skipped"
+STATUS_UNPROVEN = "unproven"
+
+# Statuses that count as a healthy answer from a probe.
+_HEALTHY_STATUSES = frozenset({STATUS_OK})
+# Statuses meaning "this probe did not run", as opposed to "it ran and failed".
+_NOT_RUN_STATUSES = frozenset({STATUS_SKIPPED})
+
+_DEEP_PROBE_TTL_ENV = "WEBUI_HEALTH_PROBE_TTL_SECONDS"
+_DEFAULT_DEEP_PROBE_TTL = 15.0
+_GITEA_PROBE_TIMEOUT_SECONDS = 5.0
+
+_OFFLINE_ENV = "WEBUI_TEST_OFFLINE"
+
+# Credential-shaped material that must never reach the browser, mirroring the
+# forbidden client patterns in webui/deployment_boundary.py.
+_SECRET_RE = re.compile(
+    r"(?i)\b(token|password|passwd|secret|authorization|bearer)\b\s*[:=]?\s*\S+"
+)
+_LONG_OPAQUE_RE = re.compile(r"\b[A-Za-z0-9_\-]{32,}\b")
+
+# Captured once at import so uptime measures this process, not the request.
+_STARTED_AT = datetime.now(timezone.utc)
+_STARTED_MONOTONIC = time.monotonic()
+
+# TTL cache for the expensive (network) probe only.
+_deep_cache: dict[str, tuple[float, "DependencyProbe"]] = {}
+
+
+@dataclass(frozen=True)
+class DependencyProbe:
+    """One dependency check, fail-soft, with its own latency."""
+
+    name: str
+    kind: str
+    status: str
+    detail: str
+    required: bool
+    latency_ms: float | None = None
+    metadata: dict[str, Any] | None = None
+
+    @property
+    def healthy(self) -> bool:
+        return self.status in _HEALTHY_STATUSES
+
+    @property
+    def ran(self) -> bool:
+        return self.status not in _NOT_RUN_STATUSES
+
+
+@dataclass(frozen=True)
+class VersionInfo:
+    git_sha: str | None
+    git_describe: str | None
+    control_plane_schema_version: int | None
+    python_version: str
+    known: bool
+
+
+@dataclass(frozen=True)
+class StaleRuntime:
+    """Parity between the running code, the checkout, and the remote.
+
+    ``mutation_safe`` is deliberately conservative: unknown is not safe.
+    """
+
+    daemon_head: str | None
+    checkout_head: str | None
+    remote_head: str | None
+    stale: bool
+    determinable: bool
+    mutation_safe: bool
+    reasons: tuple[str, ...]
+
+
+@dataclass(frozen=True)
+class SystemHealthSnapshot:
+    status: str
+    ready: bool
+    readiness_complete: bool
+    readiness_reasons: tuple[str, ...]
+    service: str
+    mode: str
+    version: VersionInfo
+    started_at: str
+    uptime_seconds: float
+    timestamp: str
+    deep_probes_requested: bool
+    dependencies: tuple[DependencyProbe, ...]
+    mcp_namespaces: tuple[dict[str, Any], ...]
+    stale_runtime: StaleRuntime
+    probe_errors: tuple[str, ...] = ()
+
+
+def process_uptime() -> tuple[str, float]:
+    """Process start timestamp and uptime — in-memory, safe for `/health`."""
+    return _STARTED_AT.isoformat(), round(time.monotonic() - _STARTED_MONOTONIC, 3)
+
+
+def _offline() -> bool:
+    return (os.environ.get(_OFFLINE_ENV) or "").strip().lower() in {"1", "true", "yes"}
+
+
+def _repo_root() -> Path:
+    override = (os.environ.get("WEBUI_REPO_ROOT") or "").strip()
+    if override:
+        return Path(override).resolve()
+    return Path(__file__).resolve().parent.parent
+
+
+def _deep_probe_ttl() -> float:
+    raw = (os.environ.get(_DEEP_PROBE_TTL_ENV) or "").strip()
+    if not raw:
+        return _DEFAULT_DEEP_PROBE_TTL
+    try:
+        value = float(raw)
+    except ValueError:
+        return _DEFAULT_DEEP_PROBE_TTL
+    return value if value >= 0 else _DEFAULT_DEEP_PROBE_TTL
+
+
+def redact(text: str) -> str:
+    """Strip credential-shaped material from operator-visible probe text.
+
+    Probe details carry exception strings, and an exception raised by an HTTP
+    client can quote the request that failed. Redaction happens here, at the
+    boundary where those strings become part of a browser-bound payload.
+    """
+    if not text:
+        return ""
+    cleaned = _redact_urls(text)
+    cleaned = _SECRET_RE.sub(lambda m: f"{m.group(1)}=[redacted]", cleaned)
+    return _LONG_OPAQUE_RE.sub("[redacted]", cleaned)
+
+
+def _redact_urls(text: str) -> str:
+    return re.sub(r"https?://\S+", lambda m: redact_url(m.group(0)), text)
+
+
+def redact_url(url: str) -> str:
+    """Reduce a URL to scheme://host/path — no userinfo, no query, no fragment."""
+    try:
+        parts = urlsplit(url)
+    except ValueError:
+        return "[redacted-url]"
+    if not parts.scheme or not parts.hostname:
+        return "[redacted-url]"
+    netloc = parts.hostname
+    if parts.port:
+        netloc = f"{netloc}:{parts.port}"
+    return urlunsplit((parts.scheme, netloc, parts.path, "", ""))
+
+
+def _git(repo: Path, *args: str) -> str | None:
+    try:
+        completed = subprocess.run(
+            ["git", "-C", str(repo), *args],
+            capture_output=True,
+            text=True,
+            check=False,
+            timeout=10,
+        )
+    except (OSError, subprocess.SubprocessError):
+        return None
+    if completed.returncode != 0:
+        return None
+    return (completed.stdout or "").strip() or None
+
+
+def _load_version(repo: Path, *, schema_version: int | None) -> VersionInfo:
+    import platform
+
+    git_sha = None if _offline() else _git(repo, "rev-parse", "HEAD")
+    describe = None if _offline() else _git(repo, "describe", "--tags", "--always")
+    return VersionInfo(
+        git_sha=git_sha,
+        git_describe=describe,
+        control_plane_schema_version=schema_version,
+        python_version=platform.python_version(),
+        known=bool(git_sha),
+    )
+
+
+# ---------------------------------------------------------------------------
+# Dependency probes
+# ---------------------------------------------------------------------------
+
+
+def _elapsed_ms(started: float) -> float:
+    return round((time.monotonic() - started) * 1000, 3)
+
+
+def probe_control_plane_db(db_path: str | None = None) -> DependencyProbe:
+    """Read-only reachability check for the control-plane SQLite substrate.
+
+    Opened through a ``mode=ro`` URI on purpose: ``ControlPlaneDB.__init__``
+    creates directories and runs schema migrations, which a health check must
+    never do.
+    """
+    path = (db_path or control_plane_db.default_db_path()).strip()
+    started = time.monotonic()
+    metadata: dict[str, Any] = {"path": path}
+
+    def _result(status: str, detail: str) -> DependencyProbe:
+        return DependencyProbe(
+            name="control_plane_db",
+            kind="sqlite",
+            status=status,
+            detail=detail,
+            required=True,
+            latency_ms=_elapsed_ms(started),
+            metadata=metadata,
+        )
+
+    if not path or not os.path.exists(path):
+        return _result(STATUS_DOWN, "control-plane database file does not exist yet")
+    try:
+        conn = sqlite3.connect(f"file:{path}?mode=ro", uri=True, timeout=5)
+        try:
+            row = conn.execute(
+                "SELECT value FROM schema_meta WHERE key = 'schema_version'"
+            ).fetchone()
+            leases = conn.execute(
+                "SELECT COUNT(*) FROM leases WHERE status = 'active'"
+            ).fetchone()
+        finally:
+            conn.close()
+    except sqlite3.Error as exc:
+        return _result(STATUS_DOWN, redact(f"control-plane database unreadable: {exc}"))
+
+    schema_version = int(row[0]) if row and str(row[0]).isdigit() else None
+    metadata["schema_version"] = schema_version
+    metadata["active_leases"] = int(leases[0]) if leases else None
+    if schema_version is None:
+        return _result(
+            STATUS_DEGRADED, "control-plane database has no recorded schema version"
+        )
+    if schema_version != control_plane_db.SCHEMA_VERSION:
+        return _result(
+            STATUS_DEGRADED,
+            f"control-plane schema version {schema_version} does not match the "
+            f"version this code expects ({control_plane_db.SCHEMA_VERSION})",
+        )
+    return _result(STATUS_OK, f"schema v{schema_version} readable")
+
+
+def probe_repository(repo: Path) -> DependencyProbe:
+    """Local checkout reachability — required, cheap, no network."""
+    started = time.monotonic()
+    metadata: dict[str, Any] = {"repo_root": str(repo)}
+    if _offline():
+        return DependencyProbe(
+            name="repository",
+            kind="git",
+            status=STATUS_SKIPPED,
+            detail=f"{_OFFLINE_ENV} is set; git probe skipped",
+            required=True,
+            latency_ms=_elapsed_ms(started),
+            metadata=metadata,
+        )
+    head = _git(repo, "rev-parse", "HEAD")
+    if not head:
+        return DependencyProbe(
+            name="repository",
+            kind="git",
+            status=STATUS_DOWN,
+            detail=f"HEAD could not be read at {repo}",
+            required=True,
+            latency_ms=_elapsed_ms(started),
+            metadata=metadata,
+        )
+    branch = _git(repo, "rev-parse", "--abbrev-ref", "HEAD")
+    metadata["head"] = head
+    metadata["branch"] = branch
+    return DependencyProbe(
+        name="repository",
+        kind="git",
+        status=STATUS_OK,
+        detail=f"checkout readable at {branch or 'detached HEAD'}",
+        required=True,
+        latency_ms=_elapsed_ms(started),
+        metadata=metadata,
+    )
+
+
+def probe_gitea(host: str) -> DependencyProbe:
+    """Live Gitea reachability. Expensive (network), so opt-in via ``deep``.
+
+    Optional by design: the console stays useful for local inventory when the
+    remote is unreachable, so a failure here degrades status without claiming
+    the process itself is unready.
+    """
+    started = time.monotonic()
+    metadata: dict[str, Any] = {"host": host}
+
+    def _failure(status: str, detail: str) -> DependencyProbe:
+        return DependencyProbe(
+            name="gitea",
+            kind="http",
+            status=status,
+            detail=detail,
+            required=False,
+            latency_ms=_elapsed_ms(started),
+            metadata=metadata,
+        )
+
+    if not host:
+        return _failure(STATUS_DEGRADED, "no Gitea host is configured in the registry")
+    try:
+        auth = get_auth_header(host)
+    except Exception as exc:  # noqa: BLE001 — credential guards are a status here
+        return _failure(STATUS_DEGRADED, redact(f"credential lookup refused: {exc}"))
+    if not auth:
+        return _failure(STATUS_DEGRADED, f"no credentials available for {host}")
+
+    url = gitea_url(host, "/api/v1/version")
+    metadata["endpoint"] = redact_url(url)
+    try:
+        data = api_request("GET", url, auth, timeout=_GITEA_PROBE_TIMEOUT_SECONDS)
+    except Exception as exc:  # noqa: BLE001 — a down dependency is a status
+        return _failure(STATUS_DOWN, redact(f"Gitea probe failed: {exc}"))
+
+    if isinstance(data, dict) and data.get("version"):
+        metadata["gitea_version"] = str(data["version"])
+    return DependencyProbe(
+        name="gitea",
+        kind="http",
+        status=STATUS_OK,
+        detail=f"{host} reachable",
+        required=False,
+        latency_ms=_elapsed_ms(started),
+        metadata=metadata,
+    )
+
+
+def _skipped_gitea(host: str) -> DependencyProbe:
+    return DependencyProbe(
+        name="gitea",
+        kind="http",
+        status=STATUS_SKIPPED,
+        detail="network probe not requested; call with ?deep=1 to run it",
+        required=False,
+        latency_ms=None,
+        metadata={"host": host},
+    )
+
+
+def namespace_summaries() -> tuple[dict[str, Any], ...]:
+    """Declared MCP namespaces, each honestly reported as unproven.
+
+    The web process runs outside the IDE-managed MCP client, so it cannot
+    invoke a namespace tool. Per #543 only a ``client_namespace`` probe proves
+    that path, and inventing a healthy verdict here is exactly the false claim
+    the mutation gates exist to prevent.
+    """
+    rows: list[dict[str, Any]] = []
+    for namespace, required_tool in sorted(
+        mcp_namespace_health.REQUIRED_NAMESPACE_TOOLS.items()
+    ):
+        classification = mcp_namespace_health.classify_namespace_probe(
+            namespace,
+            required_tool=required_tool,
+            probe_result=None,
+            probe_source=mcp_namespace_health.PROBE_SOURCE_UNKNOWN,
+        )
+        rows.append(
+            {
+                "namespace": namespace,
+                "required_tool": required_tool,
+                "status": STATUS_UNPROVEN,
+                "ide_namespace_proven": bool(classification.get("ide_namespace_proven")),
+                "reason": (
+                    "the web console cannot invoke the IDE-managed MCP client; "
+                    "namespace health must be proven with a client_namespace "
+                    "probe (#543)"
+                ),
+                "error_type": classification.get("error_type"),
+            }
+        )
+    return tuple(rows)
+
+
+def assess_stale_runtime(
+    repo: Path,
+    *,
+    daemon_head: str | None = None,
+    git_reader: Callable[..., str | None] | None = None,
+) -> StaleRuntime:
+    """Three-way parity view: running code, local checkout, remote-tracking ref.
+
+    ``mutation_safe`` requires all three to be known and equal. Anything less —
+    including "the remote ref was never fetched" — is reported as not safe with
+    a reason, so an operator never reads an unproven green.
+    """
+    reader = git_reader or (lambda *args: _git(repo, *args))
+    reasons: list[str] = []
+    # The offline switch suppresses real subprocess calls; an explicitly
+    # injected reader is already a substitute for them and is always used.
+    offline = _offline() and git_reader is None
+
+    checkout_head = None if offline else reader("rev-parse", "HEAD")
+    remote_head = None if offline else reader("rev-parse", "@{upstream}")
+    if offline:
+        reasons.append(f"{_OFFLINE_ENV} is set; parity commits were not read")
+    else:
+        if checkout_head is None:
+            reasons.append("local checkout HEAD could not be read")
+        if remote_head is None:
+            reasons.append(
+                "no remote-tracking commit is known for the current branch; "
+                "remote staleness is indeterminate (no fetch is performed here)"
+            )
+
+    effective_daemon = daemon_head if daemon_head is not None else checkout_head
+    if daemon_head is None:
+        reasons.append(
+            "the running MCP daemon's startup commit is not observable from the "
+            "web process; the checkout commit is reported in its place"
+        )
+
+    determinable = bool(checkout_head and remote_head and effective_daemon)
+    stale = bool(
+        determinable and len({checkout_head, remote_head, effective_daemon}) > 1
+    )
+    if stale:
+        reasons.append(
+            "runtime, checkout, and remote commits disagree; restart the MCP "
+            "server after updating the checkout before trusting capability gates"
+        )
+
+    return StaleRuntime(
+        daemon_head=effective_daemon,
+        checkout_head=checkout_head,
+        remote_head=remote_head,
+        stale=stale,
+        determinable=determinable,
+        mutation_safe=bool(determinable and not stale),
+        reasons=tuple(reasons),
+    )
+
+
+# ---------------------------------------------------------------------------
+# Snapshot assembly
+# ---------------------------------------------------------------------------
+
+
+def _default_host() -> str:
+    registry = load_registry()
+    if not registry.projects:
+        return ""
+    raw = registry.projects[0].remote_host
+    parts = urlsplit(raw.strip())
+    return parts.netloc or raw.strip().rstrip("/")
+
+
+def _aggregate(
+    probes: tuple[DependencyProbe, ...],
+) -> tuple[str, bool, bool, tuple[str, ...]]:
+    """Fold probe results into overall status and readiness.
+
+    Required probes drive readiness; optional probes can only degrade status.
+    A probe that did not run leaves readiness incomplete rather than passing.
+    """
+    reasons: list[str] = []
+    required = [probe for probe in probes if probe.required]
+    unrun_required = [probe for probe in required if not probe.ran]
+    failed_required = [probe for probe in required if probe.ran and not probe.healthy]
+    failed_optional = [
+        probe
+        for probe in probes
+        if not probe.required and probe.ran and not probe.healthy
+    ]
+
+    for probe in unrun_required:
+        reasons.append(
+            f"required dependency '{probe.name}' was not probed: {probe.detail}"
+        )
+    for probe in failed_required:
+        reasons.append(
+            f"required dependency '{probe.name}' is {probe.status}: {probe.detail}"
+        )
+    for probe in failed_optional:
+        reasons.append(
+            f"optional dependency '{probe.name}' is {probe.status}: {probe.detail}"
+        )
+
+    readiness_complete = not unrun_required
+    ready = readiness_complete and not failed_required
+
+    if any(probe.status == STATUS_DOWN for probe in failed_required):
+        status = STATUS_DOWN
+    elif failed_required or failed_optional or unrun_required:
+        status = STATUS_DEGRADED
+    else:
+        status = STATUS_OK
+    return status, ready, readiness_complete, tuple(reasons)
+
+
+def load_system_health(
+    *,
+    deep: bool = False,
+    host: str | None = None,
+    probes: tuple[DependencyProbe, ...] | None = None,
+    daemon_head: str | None = None,
+    use_cache: bool = True,
+) -> SystemHealthSnapshot:
+    """Assemble the read-only system-health snapshot.
+
+    ``deep=True`` adds the network probe against Gitea; its result is cached for
+    a short TTL so repeated dashboard polls do not amplify into remote load.
+    """
+    repo = _repo_root()
+    probe_errors: list[str] = []
+
+    if probes is None:
+        collected: list[DependencyProbe] = []
+        for probe_fn in (
+            lambda: probe_control_plane_db(),
+            lambda: probe_repository(repo),
+        ):
+            try:
+                collected.append(probe_fn())
+            except Exception as exc:  # noqa: BLE001 — a probe must not 500 the API
+                probe_errors.append(redact(f"probe raised: {exc}"))
+        resolved_host = host if host is not None else _default_host()
+        if deep and not _offline():
+            collected.append(_cached_gitea_probe(resolved_host, use_cache=use_cache))
+        else:
+            collected.append(_skipped_gitea(resolved_host))
+        probes = tuple(collected)
+
+    status, ready, readiness_complete, reasons = _aggregate(probes)
+    stale = assess_stale_runtime(repo, daemon_head=daemon_head)
+    if stale.stale:
+        if status == STATUS_OK:
+            status = STATUS_DEGRADED
+        reasons = reasons + (
+            "runtime is stale relative to its remote-tracking commit",
+        )
+
+    db_probe = next((p for p in probes if p.name == "control_plane_db"), None)
+    schema_version = None
+    if db_probe and db_probe.metadata:
+        schema_version = db_probe.metadata.get("schema_version")
+
+    return SystemHealthSnapshot(
+        status=status,
+        ready=ready,
+        readiness_complete=readiness_complete,
+        readiness_reasons=reasons,
+        service=SERVICE_NAME,
+        mode="read-only",
+        version=_load_version(repo, schema_version=schema_version),
+        started_at=_STARTED_AT.isoformat(),
+        uptime_seconds=round(time.monotonic() - _STARTED_MONOTONIC, 3),
+        timestamp=datetime.now(timezone.utc).isoformat(),
+        deep_probes_requested=deep,
+        dependencies=probes,
+        mcp_namespaces=namespace_summaries(),
+        stale_runtime=stale,
+        probe_errors=tuple(probe_errors),
+    )
+
+
+def _cached_gitea_probe(host: str, *, use_cache: bool = True) -> DependencyProbe:
+    ttl = _deep_probe_ttl()
+    now = time.monotonic()
+    if use_cache and ttl > 0:
+        cached = _deep_cache.get(host)
+        if cached and (now - cached[0]) < ttl:
+            return cached[1]
+    probe = probe_gitea(host)
+    if use_cache and ttl > 0:
+        _deep_cache[host] = (now, probe)
+    return probe
+
+
+def clear_probe_cache() -> None:
+    """Drop cached deep-probe results (tests and operator-forced refresh)."""
+    _deep_cache.clear()
+
+
+def probe_to_dict(probe: DependencyProbe) -> dict[str, Any]:
+    return {
+        "name": probe.name,
+        "kind": probe.kind,
+        "status": probe.status,
+        "detail": probe.detail,
+        "required": probe.required,
+        "healthy": probe.healthy,
+        "latency_ms": probe.latency_ms,
+        "metadata": dict(probe.metadata or {}),
+    }
+
+
+def snapshot_to_dict(snapshot: SystemHealthSnapshot) -> dict[str, Any]:
+    return {
+        "status": snapshot.status,
+        "service": snapshot.service,
+        "mode": snapshot.mode,
+        "api": API_PATH,
+        "timestamp": snapshot.timestamp,
+        "readiness": {
+            "ready": snapshot.ready,
+            "complete": snapshot.readiness_complete,
+            "reasons": list(snapshot.readiness_reasons),
+        },
+        "version": {
+            "git_sha": snapshot.version.git_sha,
+            "git_describe": snapshot.version.git_describe,
+            "control_plane_schema_version": (
+                snapshot.version.control_plane_schema_version
+            ),
+            "python_version": snapshot.version.python_version,
+            "known": snapshot.version.known,
+        },
+        "process": {
+            "started_at": snapshot.started_at,
+            "uptime_seconds": snapshot.uptime_seconds,
+        },
+        "deep_probes_requested": snapshot.deep_probes_requested,
+        "dependencies": [probe_to_dict(probe) for probe in snapshot.dependencies],
+        "mcp_namespaces": [dict(row) for row in snapshot.mcp_namespaces],
+        "stale_runtime": {
+            "daemon_head": snapshot.stale_runtime.daemon_head,
+            "checkout_head": snapshot.stale_runtime.checkout_head,
+            "remote_head": snapshot.stale_runtime.remote_head,
+            "stale": snapshot.stale_runtime.stale,
+            "determinable": snapshot.stale_runtime.determinable,
+            "mutation_safe": snapshot.stale_runtime.mutation_safe,
+            "reasons": list(snapshot.stale_runtime.reasons),
+        },
+        "probe_errors": list(snapshot.probe_errors),
+    }