[P1] Adapter.get_schema() Protocol method + schema fingerprinting + drift quarantine

[se-jo-ma]

Problem

Adapter Protocol (nautilus/adapters/base.py:127-172) defines only connect / execute / close. No get_schema() method, no schema fingerprinting infrastructure, no drift quarantine policy.

Per design §4.6 (Weakness 6 v1 mitigation): if a source's schema changes (columns added, renamed, removed), routing rules / scope constraints / transformation rules that reference those columns break silently.

Design references

• design-docs/05-ecosystem-roadmap.md:233-285 — full spec including source_schema CLIPS template + quarantine-drifted-source rule example
• design-docs/05-ecosystem-roadmap.md:411-412 — v1 roadmap items: "Adapter get_schema() method and schema fingerprinting" + "Schema drift detection and source quarantine policy rules"

Code locations to modify

• nautilus/adapters/base.py:127 — add get_schema() -> SourceSchema to Adapter Protocol
• nautilus/core/models.py — add SourceSchema model (columns, types, hash)
• Each adapter — implement get_schema() querying upstream system metadata
• nautilus/core/broker.py — schedule periodic schema check (configurable interval, default hourly), assert source_schema fact into CLIPS
• nautilus/rules/ — ship quarantine-drifted-source policy rule
• nautilus.yaml schema — add schema_check_interval per source

Acceptance

• Each adapter exposes get_schema() returning canonical column list + types.
• Schema hash stored as CLIPS fact; recomputed on configured interval.
• Hash change asserts schema_drift fact; quarantine rule fires; source excluded from routing until operator ack.
• Admin UI / CLI surfaces quarantined sources (admin UI work is v2).
• Integration test: mutate test Postgres schema, assert source quarantined within one check cycle.

Priority

P1 — listed as v1 mitigation in design doc but Protocol surface entirely missing.

[se-jo-ma]

Audit vs merged #41: fully implemented — ready to close.

• nautilus/adapters/base.py:177-189 — get_schema() on Protocol; all 8 adapters implement (information_schema / db.labels() / _mapping / SHOW MEASUREMENTS / sys_dictionary / static)
• nautilus/adapters/schema.py — AdapterSchema.fingerprint() (AC-21.a/b), classify_drift() (AC-21.d), SchemaFingerprintStore + ack (AC-21.g)
• nautilus/core/broker.py:1140-1456 — startup fingerprint check, major-drift quarantine + schema_drift_detected audit entry, request-time quarantine block
• CLI: nautilus adapters list --status / schema / schema-fingerprint / schema-diff / schema-ack