[nycomp]

Part of #970 — phase 2 (yapper↔auth cycle), single commit, base weekly.

Change

campus.yapper is now self-contained: it imports no campus package at all. The lazy from campus.auth import resources calls (the yapper↔auth cycle) are gone at the source, replaced by dependency injection at the DB-URI seam.

create() resolves the event database URI in priority order:

1. db_uri argument
2. db_uri_provider() callable — the injection point
3. YAPPERDB_URI environment variable
4. remote campus vault "campus.yapper" via campus_python (unchanged default for api's bare create() in production)

Client identity (CLIENT_ID/CLIENT_SECRET) stays env-driven, unchanged.

Callers

• campus.auth — get_yapper() now injects a provider backed by its own in-process vault (vault["campus.yapper"]["YAPPERDB_URI"]), replacing the DEPLOY=campus.auth env special-case (branch deleted; yapper no longer consults DEPLOY). The ~40 get_yapper().emit(...) call sites are untouched, and contract tests patch get_yapper by name — unaffected.
• campus.api — the three bare campus.yapper.create() route calls are untouched: production still resolves via the remote vault; in test mode the fixture exports the seeded URI as YAPPERDB_URI env.
• Test fixtures (tests/fixtures/yapper.py) — still seed the vault secret (the vault-delivery contract and its integration test are unchanged) and additionally set the env var, with a comment explaining the split.

Safety properties

• Test mode never touches the network: STORAGE_MODE=1 with no resolvable URI raises ValueError instead of falling through to the remote vault (guards issue fix(integration): yapper backend tries to connect to external service in test mode #319's class of bug).
• Boundary contract hardened (test_package_boundaries.py): yapper moves out of SERVICE_LAYERS into SHARED_ALLOWED with zero allowed campus deps — emitters may import yapper; it must never grow campus dependencies back. Statically enforced.
• New tests/unit/yapper/test_factory.py covers the resolution order and asserts at runtime (subprocess) that create() never loads campus.auth.

Verification

import campus.yapper loads only campus.yapper; bare create() under test mode runs with campus.auth unimported. Unit, contract, integration, and ruff check . all green.

Note for reviewers: this is the injection fix from the phase-2 discussion on #970. The yapper-into-campus.audit placement idea was assessed and set aside (audit never imports yapper; the move would drag audit's init into every emitter and widen the cycle into auth⇄audit).