fix(multishot): expose fatal tool errors

[drewstone]

Summary

• add MultishotFatalToolError to the multishot public API
• rethrow fatal tool executor errors instead of feeding them back as recoverable tool messages
• bump package versions to 0.96.4

Verification

• pnpm vitest run tests/multishot/multishot.test.ts
• pnpm typecheck
• python3 -m py_compile clients/python/src/agent_eval_rpc/init.py
• NODE_OPTIONS=--max-old-space-size=8192 pnpm build
• pnpm verify:package
• pnpm test
• git diff --check
• git merge-tree --write-tree origin/main HEAD

[tangletools]

✅ Auto-approved PR — 725b0ac8

Blanket team auto-approval is enabled for this reviewer service.
The full PR reviewer audit still runs separately and will publish findings if it detects issues.

_{tangletools · auto-approval · reason: blanket_auto_approve · 2026-06-22T18:18:30Z}