#9549 fix(sandbox): initialize workbench history before honoring a stop during creation

Summary

• A chat workbench created while the caller stopped (e.g. Stop pressed during the first run_code) keeps existing for the next call to reuse, but ensureSessionSandbox checked the abort before initializing the machine's input history
• The next call then reuses a machine with no history, the history script records it as unknown, and every later code/shell result in that chat is withheld ("Tool execution settled, but its result could not be returned safely") until the machine is discarded — even when the code succeeded
• Initialize the history for a newly created machine before honoring the abort. A machine this call just created has received no input, so empty history is exact; nothing changes on the non-abort path
• Existing machines latched before this ships are discarded by the paused-session sweep shortly after their last use, so no cleanup is needed

Type of Change

• Bug fix

Testing

• Added a case to session-input-certification.integration.ts (real Redis history script, code + shell): the caller stops while the provider is creating the machine, then the next call reuses it and must return its result with clean history
• Red on the pre-fix code with Workbench output withheld because its secret provenance is unavailable, green with the fix; existing certification cases unchanged
• session-file-provenance.integration.ts and all lib/execution/remote-sandbox unit tests pass (574)
• Lint, type-check, audits, and full suites run in CI

Checklist

• Code follows project style guidelines
• Self-reviewed my changes
• Tests added/updated and passing (new tests pass the test-audit authoring gate)
• No new warnings introduced
• I confirm that I have read and agree to the terms outlined in the Contributor License Agreement (CLA)