usrcp-extension

Chrome browser extension (MV3) that captures claude.ai conversations into the encrypted USRCP ledger and injects ledger context via a /usrcp <query> slash command in the composer.

v0 scope: Chrome only, claude.ai only, manual "Load Unpacked" install.

Architecture

claude.ai tab
  └── injected fetch patch  (MAIN world, bundled into service-worker.js)
        window.fetch patch → tee SSE → parse content_block_delta
        → window.postMessage → content-claude.js

  └── content-claude.js     (isolated world)
        receives turn from page hook → chrome.runtime.sendMessage → SW
        intercepts /usrcp <query> keydown → chrome.runtime.sendMessage → SW
        receives search results from SW → sets composer text

service-worker.js
  owns chrome.runtime.connectNative("com.usrcp.bridge")
  20s heartbeat to keep SW alive
  routes ledger.append + memory.search to native host

native-host/usrcp-bridge.cjs   (Node.js, stdio framing)
  reads/writes Chrome NM 4-byte LE length-prefixed JSON frames
  imports usrcp-local directly, calls Ledger.appendEvent / Ledger.searchTimeline
  no MCP server in the middle for v0

Prerequisites

• Chrome (any recent version with MV3 support — Chrome 88+)
• Node.js ≥ 20 (for the native host)
• A configured USRCP ledger: usrcp setup

Install

1. Build the extension

cd packages/usrcp-extension
npm install
npm run build

This produces dist/ containing:

• manifest.json
• service-worker.js
• content-claude.js
• setup.js + config.js (wizard modules)

2. Run the wizard

usrcp setup --adapter=extension

The wizard will:

1. Verify native-host/usrcp-bridge.cjs exists.
2. Tell you to open Chrome → chrome://extensions → Developer Mode → Load Unpacked → select packages/usrcp-extension/dist/.
3. Prompt you to paste the extension ID shown in chrome://extensions.
4. Write a pinned-Node native host launcher under ~/.usrcp/native-host/.
5. Write the Chrome Native Messaging manifest at: ~/Library/Application Support/Google/Chrome/NativeMessagingHosts/com.usrcp.bridge.json
6. Write ~/.usrcp/extension-config.json (mode 0600).

3. Reload the extension

After the wizard completes, click the reload icon on the USRCP extension card in chrome://extensions to pick up the newly installed NM manifest.

Usage

Capture (automatic)

Once the extension is loaded and the native host is installed, every claude.ai conversation is automatically captured into your USRCP ledger. The capture happens at the network layer (fetch patch) — no DOM scraping.

Slash command (inject context)

In any claude.ai composer, type:

/usrcp <your query>

Press Enter. The extension:

1. Prevents the line from being sent as a prompt.
2. Searches your ledger for relevant context.
3. Replaces the composer content with:

   Context from my USRCP ledger:
   > [2026-04-20] We discussed the USRCP architecture...
   > [2026-04-18] Implemented the Discord adapter...
   

4. You review, edit if needed, and send the augmented prompt yourself.

The augmentation is always visible and editable — no silent prompt rewriting.

Verification

After loading the extension and running setup:

1. Open claude.ai and send a test message.
2. Check that a turn was captured:

   usrcp status

3. Type /usrcp test in the composer and press Enter. You should see context snippets appear (or "no results" if the ledger is empty).

Environment variable

If your ledger uses a passphrase, set USRCP_PASSPHRASE in your shell environment before Chrome starts (macOS: add to ~/.zshrc / ~/.bash_profile, then restart Chrome). The native host inherits the environment from the shell that launched Chrome.

export USRCP_PASSPHRASE="your-passphrase"

Troubleshooting

Extension shows "Could not establish connection" in the console:

• The native host is not installed or the extension ID in the NM manifest is wrong.
• Re-run usrcp setup --adapter=extension and paste the correct extension ID.

/usrcp slash command does nothing:

• The composer selector may have changed. Check the browser console for errors.
• File an issue with the DOM structure of the composer at your claude.ai version.

Captures not appearing in usrcp status:

• Check for errors in the extension's service worker console (chrome://extensions → USRCP → "Service Worker" link → Console).
• Verify USRCP_PASSPHRASE is set if you use passphrase mode.

NM host fails to start:

• Ensure native-host/usrcp-bridge.cjs is executable: chmod +x native-host/usrcp-bridge.cjs
• Ensure node is on your PATH (the shebang uses /usr/bin/env node).

Deferred to v0.1

• Firefox support — ~30-line manifest variant; requires browser_specific_settings and the Firefox NM manifest path.
• Stable extension ID — unpacked loads get a random ID based on source path. A published key field in manifest.json makes it stable; requires Chrome Web Store coordination.

Deferred to v0.5

• Sidebar / ledger browser UI.
• ChatGPT support (/backend-api/conversation).

Deferred (open question)

• Reproducible build pipeline + Web Store publication. Trust budget for AI-chat-reading extensions is thin; source-verifiable builds are important. Tracked in the PR as an open question.

Permissions

Requested: nativeMessaging, storage, scripting Host permissions: https://claude.ai/* only

NOT requested: <all_urls>, cookies, webRequest, tabs (broad form), history, downloads.