Connectors: framework, policy, and the PostgreSQL backend

What it is

A connector declares static capabilities (its name, whether it writes, which dialect) and the registry refuses to hold one that does not satisfy the contract. Acquisition goes through the registry, so the framework is the only way a connector is built.

registry = ConnectorRegistry(tracer=tracer, emitter=emitter)
registry.register(PostgresConnector)

async with registry.build("postgres").opened(target=config, context=context) as conn:
    rows = await conn.execute(statement=compiled.text,
                              params=tuple(compiled.parameters.items()))

The decisions that carry weight

ConnectionPolicy extends the adapter-local idiom rather than replacing it. The reliability inventory found timeouts and bounded retry already implemented per adapter, so the policy adds only what was genuinely absent - circuit breaking and half-open recovery - and consults the existing is_retryable() taxonomy, which finally gives that public contract a caller in src/.

Declared capabilities are enforced, not decorative. This connector says writes=False and refuses a statement that is not a read; a declaration nothing acts on is a comment.

The engine is built per open from the resolved target, never from a stored DSN, because a stored DSN is a credential that outlives its rotation. The tenant in the authorized context must match the target's tenant or the connection refuses to open.

Evidence

19 test functions across tests/unit/test_connector_framework.py and tests/integration/test_postgres_connector.py, run with the project gate:

.venv/Scripts/python.exe -m pytest tests/unit/test_connector_framework.py -q
.venv/Scripts/python.exe -m pytest tests/integration/test_postgres_connector.py -q

Parametrized cases expand these functions further; the counts here are functions, which is what the documentation check verifies.

Limits

PostgreSQL only. Snowflake, MongoDB, StarRocks and BigQuery have no module and no export - a connector class in the public surface is a claim that it works, and the absence is asserted by a test rather than promised in a roadmap. The retry budget, worker retry, dead-letter handling, security-context preservation during retries and shutdown drain remain open (§06-reliability-inventory).