Add the E2B extension for Pi (@e2b/pi)

[tomasvarga]

Adds @e2b/pi, the E2B extension for Pi. With pi --e2b, Pi stays on your machine and its tools run in an E2B sandbox that belongs to the Pi session.

What it does

• Tools in the sandbox. bash, read, write, edit and ! commands run in the sandbox through Pi's pluggable tool operations. grep, find and ls are off in E2B mode. If there is no sandbox, tools fail and never run on the host.
• Lazy start. Pi opens at once. The sandbox starts with the first prompt and gets the git working tree (tracked and new files, with uncommitted changes). Ignored files such as .env stay local.
• Pull. /e2b pull diffs the sandbox against an upload baseline and runs git apply locally. /e2b pull --branch commits to pi/<session> instead.
• Resume and fork. pi --e2b -c reconnects to the same sandbox (paused with memory). A forked session gets its own copy via Sandbox.fork.
• Preview. preview_url gives a public link for a port.
• Cleanup. Sandboxes that no Pi session refers to are killed on the next start (same machine, Pi's own session folder only). --no-session offers a pull, then kills on exit.
• No credentials in the sandbox. No clone, no push, no host env forwarded.

Layout

index.ts          flags, session lifecycle, /e2b command, cleanup
src/tools.ts      sandbox-backed bash, read, write and edit; preview_url
src/workspace.ts  upload the working tree, diff and pull changes back

Tests

• npm run check: typecheck, oxlint (anti-slop rules, curly), oxfmt, offline smoke test
• npm run test:live: real sandbox, 10/10 steps pass (tools, background processes, abort, pause and resume, upload and pull, lazy start, fork)

Linear: INT-149