Keep hard /^cdp/ fallback + content last-resort covered by regression tests

[Trace824]

Summary

Hard CDP fallback (/^cdp[A-Z]/ → executeCDPToolDirect) in the bridge and the content-script Unknown-tool forwarder are production safety nets for insert_text. They are easy to regress without automated coverage.

Repro

• Context: Unpacked extension with current bridge + messaging patches; MCP calling CDP verbs by wire name.
• Steps:
  1. Force resolve to return null (or simulate missing getToolByNameOrVerb).
  2. Dispatch tool name cdpInsertText (or MCP insert_text that wires that verb).
  3. Confirm path hits executeCDPToolDirect / method: cdp_direct rather than Unknown tool.
• Observed without fallback: hard fail. With fallback (local branch): success.

Code pointers (verified against /workspace/FSB)

• extension/ws/mcp-bridge-client.js — /^cdp[A-Z]/ fallback (~L1908–1924).
• extension/content/messaging.js — last-resort CDP forward (~L1062–1088).
• extension/background.js — executeCDPToolDirect (~L19786+), cdpInsertText (~L20055+).
• tests/ — add focused unit tests under existing patterns (no dedicated CDP-fallback test found yet; likely area: new test beside bridge/dispatcher tests).

Proposed fix

Add regression tests that (1) bridge routes unresolved cdpInsertText to executeCDPToolDirect, and (2) content messaging forwards /^cdp/ instead of returning Unknown tool. Keep the fallbacks; do not remove them as “dead code.”

Acceptance / regression

• CI fails if either fallback is deleted or gated behind a broken resolve-only path.
• Manual: insert_text on x.com compose reports success via CDP path after SW stress.

Owner

extension

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Priority: P1 · Owner: extension

[LakshmanTurlapati]

Fixed in #143: wire-verb routing is now covered by tests/mcp-wire-verb-routing.test.js, which asserts CDP verbs reach the CDP path instead of "Unknown tool".