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>

Dockerfile

@@ -0,0 +1,29 @@
+FROM python:3.12-slim
+
+# I-12: the sha is baked HERE, at build time, from the artifact's own stamp.
+# A runtime COMMIT_SHA env var is ignored by api/app/buildinfo.py. This is the
+# structural fix for nine sibling services that cannot name their own commit.
+ARG COMMIT_SHA=""
+ARG BUILT_AT=""
+
+WORKDIR /app
+RUN apt-get update && apt-get install -y --no-install-recommends git curl \
+    && rm -rf /var/lib/apt/lists/*
+
+COPY pyproject.toml ./
+RUN pip install --no-cache-dir -e .
+
+COPY api ./api
+COPY alembic ./alembic
+COPY alembic.ini scripts ./
+COPY scripts ./scripts
+
+RUN sed -i "s|^BAKED_COMMIT_SHA: str = \"\"|BAKED_COMMIT_SHA: str = \"${COMMIT_SHA}\"|" api/app/buildinfo.py \
+ && sed -i "s|^BAKED_BUILT_AT: str = \"\"|BAKED_BUILT_AT: str = \"${BUILT_AT}\"|" api/app/buildinfo.py \
+ && grep -q "BAKED_COMMIT_SHA: str = \"${COMMIT_SHA}\"" api/app/buildinfo.py
+
+EXPOSE 8600
+HEALTHCHECK --interval=30s --timeout=5s --start-period=10s \
+  CMD curl -fsS http://localhost:8600/health || exit 1
+
+CMD ["uvicorn", "api.app.main:app", "--host", "0.0.0.0", "--port", "8600"]