Sync to coordinated core release: principal/subject split, attachment atomicity, guard removal

[cuibonobo]

Summary

Bumps @haverstack/core to the coordinated release (0.9.0) now that its packaging blocker (core#167) has cleared, and does the three-issue sync batch that depended on it in one pass:

• Principal/subject: adopt forSession(); lookupToken().entityId no longer exists and will break silently on upgrade #50 — Adopts forSession() and the principal/subject split everywhere the server resolves identity (auth middleware, every route, token issuance), replacing the removed TokenSession.entityId field. POST /tokens gains onBehalfOf; GET /records gains ?principalId=.
• Upgrade to the coordinated core release: one copy of core, delete superseded route guards, rewrite the tests that assert old behaviour #51 (discharges Core sync: shed route-level policy special cases as core invariants land (core #59, #57, #65, #67) #41) — Deletes the three route-level policy guards (and the unscoped stack.get() pre-fetch backing them) now that ScopedStack enforces them natively, and adds coverage for the invariants that arrive free: _config protection, _app binding rules, reserved content keys, non-owner _attachment@1 create refusal, the version-history write gate, and permission stripping on snapshots. Pins double-open protection and documents the WAL sidecar files.
• POST /attachments must store bytes and create the _attachment@1 record atomically, returning the record #52 (folds in Attachment upload buffers the entire body in memory before the size check #46) — POST /attachments now stores bytes and creates the _attachment@1 record atomically via ScopedStack.putAttachment(), returning the record instead of a bare fileId, and enforces the size limit while streaming the body instead of buffering first.

Also adopts the wire-format's typed error body ({error:{code,message}}) repository-wide via wire-types' serializeError(), since #52 specified it for the new attachment denials and the alternative was a one-off shape that would need redoing once #33 lands anyway.

Test plan

• pnpm typecheck
• pnpm lint
• pnpm build
• pnpm test — 115 tests passing, including new coverage for delegation, _config/_app/reserved-key invariants, version-history write-gating, permission stripping, and double-open protection

Closes #50, #51, #52.

https://claude.ai/code/session_01HSEQ51HctZ9fVqsS8ooNmY

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