fix(rpc): bump practice writer protocol to runtime-rpc v2 (#328 P2)

[Ancienttwo]

After #348 replaced the runtime RPC checkpoint method with practiceCheckpoint, both peers still advertised archcontext.runtime-rpc/v1. A new client could therefore treat an old daemon as compatible and miss the upgrade diagnosis. This independent follow-up closes the post-#348 RPC P2; refs #328.

The active protocol is now archcontext.runtime-rpc/v2, aligned across the current product manifest, schema, valid fixture, and fast hook. Header and body mismatches return HTTP 426 with the existing exact error string, expected/received versions, and archctx daemon upgrade. The hook keeps its existing fail-open contract and reports the version mismatch in its message. Connection format version: 1 and package/product release versions remain unchanged.

Regression coverage:

• v1 → v2 header and header-less body rejection, and v2 → frozen-v1 peer rejection with the CLI reporting rpc-version-mismatch and received=v1.
• Discovery leaves connection/lock bytes unchanged. A live frozen-v1 transport peer is replaced by PID/SIGTERM through the real CLI upgrade flow, producing a healthy v2 connection without a legacy RPC shutdown call.
• Rejected prepare and practiceCheckpoint calls leave the real practice baseline, every SQLite table, database/WAL bytes, and session rows unchanged; openSession and baseline/session writes remain at zero.
• Normal v2 health and explicit practice writer calls succeed; legacy RPC checkpoint remains rejected without dispatch.

Validation: focused pre-change tests fail on the v1 constant/400 response; final related suites pass with 515 pass, 1 existing platform-conditional skip, 0 fail across 12 files. bun run typecheck, node scripts/package-boundary-audit.mjs, git diff --check, and node scripts/packaged-cli-smoke.mjs pass. File-backed plan received Claude read-only approval before implementation.

Scope: RPC P2 only; no U4/#349 main.ts or scanner changes, D5–D7, release, aliases, historical evidence, or prior PR/comment rewrites. Keep Draft; no merge/deploy.

[chatgpt-codex-connector]

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-14T10:07:43.215848Z	401d2b3	Draft marked ready

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