fix(rag): migrate chunks_* tables to in-house vector-store schema

The in-house RAG engine (which replaced piragi) reads/writes a `content`
column and a `created_at` column on every chunks_<index_type> table and
provisions them at runtime via CREATE TABLE IF NOT EXISTS. On databases that
already carried the piragi-era tables (column `text`, no `created_at`) that
DDL is a silent no-op, so the engine never reshapes them and every
ingest/search/list fails with `column "content" ... does not exist`.

Migration 030 ALTERs each existing chunk table in place — renames
text -> content and adds created_at — preserving the non-rebuildable agent
knowledge (journals, decisions, errors, learnings, reviews, conversations)
that a docs reindex cannot regenerate. It guards on actual column presence,
so it is idempotent and safe on piragi-shaped, already-correct, or absent
tables (e.g. chunks_code).

Adds a guard test pinning the migration's table list to the IndexType enum so
a new index type cannot silently escape the schema alignment.

tests/unit/services/optimal_brain/test_chunk_schema_migration.py

@@ -0,0 +1,60 @@
+"""Guard the 030 chunk-schema migration against IndexType drift.
+
+The migration that aligns the ``chunks_<index_type>`` tables with the in-house
+vector store hardcodes the table list (so it stays self-contained and never
+imports evolving app code). This test is the other half of that contract: it
+fails the moment a new ``IndexType`` is added without extending the migration,
+which is exactly the gap that let the piragi-era ``text`` columns survive the
+engine swap and break every ingest/search.
+"""
+
+from __future__ import annotations
+
+import importlib.util
+from pathlib import Path
+from typing import TYPE_CHECKING
+
+import pytest
+from roboco.models.optimal import IndexType
+
+if TYPE_CHECKING:
+    from types import ModuleType
+
+
+def _repo_root() -> Path:
+    for parent in Path(__file__).resolve().parents:
+        if (parent / "alembic" / "versions").is_dir():
+            return parent
+    raise RuntimeError("could not locate alembic/versions from the test file")
+
+
+@pytest.fixture(scope="module")
+def migration() -> ModuleType:
+    path = _repo_root() / "alembic" / "versions" / "030_rag_chunks_content_schema.py"
+    spec = importlib.util.spec_from_file_location("_migration_030", path)
+    assert spec is not None and spec.loader is not None
+    module = importlib.util.module_from_spec(spec)
+    spec.loader.exec_module(module)
+    return module
+
+
+def test_chunk_tables_match_index_type_enum(migration: ModuleType) -> None:
+    expected = {f"chunks_{t.value}" for t in IndexType}
+    assert set(migration.CHUNK_TABLES) == expected, (
+        "CHUNK_TABLES is out of sync with IndexType — a new index type was added "
+        "without extending the 030 chunk-schema migration."
+    )
+
+
+def test_chunk_tables_has_no_duplicates(migration: ModuleType) -> None:
+    assert len(migration.CHUNK_TABLES) == len(set(migration.CHUNK_TABLES))
+
+
+def test_revision_chain_is_wired(migration: ModuleType) -> None:
+    assert migration.revision == "030_rag_chunks_content_schema"
+    assert migration.down_revision == "029_project_quality_command"
+
+
+def test_upgrade_and_downgrade_are_callable(migration: ModuleType) -> None:
+    assert callable(migration.upgrade)
+    assert callable(migration.downgrade)