G0: cell substrate — invariants made executable

Strand G0 complete and VERIFIED against real Postgres, not asserted.

  - FastAPI plane, fail-closed provider seams, repair-pointer error taxonomy
  - migration 001: all 10 tables incl. repo_type NOT NULL and model_cards (I-7)
  - 17 invariant tests, ruff clean, vocabulary audit clean

Two bugs found by RUNNING it that review would not have caught:

  1. SQLAlchemy Enum persists .name, not .value — so RepoState.deleted_soft
     and CreatedVia.imported would have written labels migration 001 never
     declared, failing at runtime rather than at review. Pinned via
     values_callable.
  2. op.create_table asks each Enum to emit its own CREATE TYPE with no
     checkfirst, so the second reference raised DuplicateObject and the
     migration died halfway. Types are now created once, referenced with
     create_type=False.

Proven live, with the hostile env var set:
  - I-12: COMMIT_SHA=deadbeef... in the environment, /version reports real HEAD.
    That env pin is the documented root cause of nine sibling services
    misreporting their commit; here it is structurally ignored.
  - I-8: three unconfigured providers -> status degraded, HTTP 503, each saying
    'refusing to report healthy'. No mock, no false green.
  - G0.4: upgrade -> downgrade -> upgrade round-trip clean (10 -> 0 -> 10).

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

api/app/providers/registry.py

@@ -0,0 +1,128 @@
+"""Concrete providers: Gitea, R2, Eternitas, Postgres, tunnel.
+
+Each is a real probe against the real dependency (I-8). None of them has a mock
+mode. If you find yourself adding one, add it behind `configured` returning False
+instead — an unconfigured provider is honest; a mock provider is a liar with a
+green light.
+"""
+
+from __future__ import annotations
+
+import httpx
+from sqlalchemy import text
+from sqlalchemy.ext.asyncio import AsyncEngine
+
+from api.app.config import Settings
+from api.app.providers.base import ProbeResult, Provider
+
+_TIMEOUT = httpx.Timeout(5.0, connect=3.0)
+
+
+class GiteaProvider(Provider):
+    """Gitea is a COMPONENT behind an API membrane, never a merged tree (I-1)."""
+
+    name = "gitea"
+
+    def __init__(self, settings: Settings) -> None:
+        self._s = settings
+
+    @property
+    def configured(self) -> bool:
+        return self._s.gitea_configured
+
+    async def probe(self) -> ProbeResult:
+        async with httpx.AsyncClient(timeout=_TIMEOUT) as client:
+            r = await client.get(
+                f"{self._s.gitea_base_url}/api/v1/version",
+                headers={"Authorization": f"token {self._s.gitea_admin_token}"},
+            )
+        if r.status_code != 200:
+            return ProbeResult(False, f"gitea /api/v1/version -> {r.status_code}", True)
+        return ProbeResult(True, f"gitea {r.json().get('version', '?')}", True)
+
+
+class R2Provider(Provider):
+    """I-3: LFS, releases, artifacts, archives. NEVER git object stores."""
+
+    name = "r2"
+
+    def __init__(self, settings: Settings) -> None:
+        self._s = settings
+
+    @property
+    def configured(self) -> bool:
+        return self._s.r2_configured
+
+    async def probe(self) -> ProbeResult:
+        # HEAD the bucket via the S3 endpoint. boto3 is sync, so we keep the
+        # probe to a plain reachability check here and let G4 wire the signed
+        # client; a 400/403 still proves the endpoint is real and answering.
+        async with httpx.AsyncClient(timeout=_TIMEOUT) as client:
+            r = await client.head(f"{self._s.r2_endpoint_url}/{self._s.r2_bucket_lfs}")
+        reachable = r.status_code < 500
+        return ProbeResult(
+            ok=r.status_code in (200, 400, 403),
+            detail=f"r2 endpoint -> {r.status_code}",
+            reachable=reachable,
+        )
+
+
+class EternitasProvider(Provider):
+    """The one issuer. Every agent identity in the ecosystem terminates here."""
+
+    name = "eternitas"
+
+    def __init__(self, settings: Settings) -> None:
+        self._s = settings
+
+    @property
+    def configured(self) -> bool:
+        return self._s.eternitas_configured
+
+    async def probe(self) -> ProbeResult:
+        async with httpx.AsyncClient(timeout=_TIMEOUT) as client:
+            r = await client.get(f"{self._s.eternitas_base_url}/health")
+        return ProbeResult(r.status_code == 200, f"eternitas /health -> {r.status_code}", True)
+
+
+class DatabaseProvider(Provider):
+    """Postgres is truth. Gitea's own DB is a component's private state."""
+
+    name = "db"
+
+    def __init__(self, engine: AsyncEngine | None) -> None:
+        self._engine = engine
+
+    @property
+    def configured(self) -> bool:
+        return self._engine is not None
+
+    async def probe(self) -> ProbeResult:
+        assert self._engine is not None
+        async with self._engine.connect() as conn:
+            await conn.execute(text("SELECT 1"))
+        return ProbeResult(True, "postgres reachable", True)
+
+
+class TunnelProvider(Provider):
+    """cloudflared is the only ingress. No inbound port is ever opened (G1.2)."""
+
+    name = "tunnel"
+
+    def __init__(self, settings: Settings) -> None:
+        self._s = settings
+
+    @property
+    def configured(self) -> bool:
+        # The tunnel is a host-level concern, not a credential we hold, so there
+        # is nothing to "configure" here. The probe alone decides health, and in
+        # dev it will honestly say cloudflared is not running (I-8).
+        return True
+
+    async def probe(self) -> ProbeResult:
+        async with httpx.AsyncClient(timeout=_TIMEOUT) as client:
+            try:
+                r = await client.get("http://localhost:2000/metrics")
+            except httpx.RequestError as exc:
+                return ProbeResult(False, f"cloudflared metrics unreachable: {exc}")
+        return ProbeResult(r.status_code == 200, f"cloudflared metrics -> {r.status_code}", True)