test(server): pin mutation/command error paths with wire-level tests

[grrowl]

Executes plan 001 from the advisor audit (deep audit @ 8e157ef). Tests only — no src changes.

What

9 wire-level tests in tests/error-paths.test.ts (+ a throwing boom command in the test worker) pinning the previously-untested error paths:

• execute throw mid-transactionSync → rejected, rolled back, no delta leak
• whole-batch rollback when op 2 of a multi-op mutation throws
• authorize failure on op 2 rejects before any write
• unknown mutation type / unknown command (UNKNOWN_COMMAND) rejections
• retried rejected txId replays the rejection (exactly-once in failure)
• retention-floor reconnect: reset followed by fresh snapshot, order asserted
• readSyncSnapshot throws on unknown collection

Review notes

• Adversarially reviewed: done criteria re-run, scope clean, tests audited as falsifiable.
• One documented deviation, verified correct on merit: the floor-reset test needed 3 rows/prune-2 (the plan's 2-row setup lands on the since >= floor-1 catch-up branch by design).

Base for the stacked PRs #—(004) and #—(005).

🤖 Generated with Claude Code

[grrowl]

Superseded by #11, which landed plan-001 on main (adapted for main + published @tanstack/db, validated green) as part of the 0.3.2 bug-fix batch.

Not merging into feat/ssr: feat/ssr will receive this via its rebase onto the new main, so merging here would duplicate/conflict with that. Closing as superseded.

The advisor/* branch is retained (not deleted) until the feat/ssr reconciliation is done — it's the source for restoring any feat/ssr-specific bits (e.g. the readSyncSnapshot test case, the extracted scheduleReconnect method) that main's adapted versions intentionally omit.