feat(chrome): hand snapshots to context mode

pi-chrome/CONTRIBUTING.md

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+# Contributing to pi-chrome
+
+Thanks for considering a contribution. pi-chrome aims to be the **de-facto browser-control toolkit for Pi agents** — that means a few non-negotiables.
+
+## Non-negotiables
+
+1. **No re-login.** Every change must keep working against the user's already-signed-in Chrome profile. Anything that requires a fresh profile or extra auth steps is out of scope.
+2. **Verifiable action results.** Input tools must return structured details and support `includeSnapshot` where verification matters. Agents need enough evidence to avoid blind retries.
+3. **Chrome real input.** Interactive controls use Chrome's input layer through `chrome.debugger`; do not re-expose synthetic/untrusted input as public UX.
+4. **Benchmarks gate features.** Add a page in `test-suite/` that fails before your change and passes after. We accept PRs faster when there's a green/red verdict to point at.
+
+## Local dev
+
+```bash
+# Link from a checkout
+pi install ./pi-chrome
+
+# Run the benchmark dashboard
+cd test-suite
+python3 -m http.server 8765
+# open http://127.0.0.1:8765/ in the Chrome window pi-chrome controls
+```
+
+## Adding a new tool
+
+1. Register in `extensions/chrome-profile-bridge/index.ts` (the `register*Tool` calls near line 840+).
+2. Implement the handler in `extensions/chrome-profile-bridge/browser-extension/service_worker.js`.
+3. Return structured details and support `includeSnapshot` for user-visible state changes when relevant.
+4. Add a benchmark page under `test-suite/challenges/` and a manifest entry.
+5. Update `README.md` "What an agent gets" table.
+6. Add a `CHANGELOG.md` entry.
+
+## Filing a bug
+
+Include:
+
+- `/chrome doctor` output
+- `pi-chrome` version + extension version (the `doctor` output prints both)
+- The exact tool call + the result envelope you got
+- Page URL or a minimal repro page in `test-suite/`
+
+## Releasing
+
+- Bump `package.json` version.
+- Move `CHANGELOG.md` notes from the working section to the new version header.
+- `npm publish --access public`.
+
+## Code of conduct
+
+Be kind, be precise, ship things. PRs that break the "no re-login" promise will be closed with a note explaining which non-negotiable they hit.