Crash handler — restore terminal, flush session, offer resume

[aakashrajput]

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Why

A fatal error mid-session currently loses the terminal state and can lose the last bits of session progress. Sessions are precious — crashes should degrade gracefully.

What

Process-level crash handler:

• process.on("uncaughtException") + unhandledRejection: restore the terminal (leave alt-screen, show cursor, disable mouse), flush the current session JSONL to disk, print a short message with the session id and a klaatai chat --resume <id> hint, exit non-zero
• Detect startup crash loops: if the last run crashed during boot (marker file), start with a safe-mode hint (skip plugins/MCP) instead of crashing identically again

Where to start

• src/engine/app.ts / src/engine/terminal.ts — terminal teardown helpers already exist
• Session persistence: session-save path in src/screens/repl.ts
• Marker file under ~/.klaatai/

Acceptance criteria

• Simulated throw inside a running REPL restores the terminal and prints the resume hint
• Session file is intact and resumable afterwards
• typecheck + tests green