[Juliusolsson05]

Summary

• Documents issue Audit and harden behavior with multiple Agent Code instances open #147 investigation and chooses a single-primary-process policy.
• Adds a shared-state advisory process lock under ~/.config/agent-code to catch dev/prod or app-identity splits that bypass Electron's single-instance lock.
• Hardens setup.json and worktree-activity-index.json writes with unique temp+rename paths, and adds a focused process-lock test.

Tests

• npm run test:process-lock
• npm run test:worktree-activity
• npm run test:review-fixes

Checks that did not pass

• npx tsc --noEmit -p tsconfig.node.json still fails on existing package alias/type issues around agent-voice-dictation, claude-code-headless, codex-headless, and pidusage.
• npm run build fails before app compilation because packages/claude-code-headless/src/proxy/mitmAddon.py is missing in this checkout; the existing Vite resource-copy plugin expects that file.

Notes

This PR intentionally does not attempt true multi-instance storage support. The current architecture stores whole workspace snapshots and process-local main registries, so the smallest defensible policy is one primary process. Future multi-window support should add windows to the primary process rather than launching multiple mains.

Closes #147