feat(chat-swarm-runtime): add existing Chrome session control

[James3014]

Summary

Part of #117 Wave 3 / G1. Rebind the existing macOS Chat Swarm runtime to an explicitly authorized existing Chrome session without creating a second worker/task/runtime authority.

This PR:

• adds explicit DEVSPACE_CHAT_SWARM_CDP_MODE=existing-session configuration;
• reads only the selected Chrome user-data-dir DevToolsActivePort endpoint artifact and opens one bounded browser-control WebSocket per lifecycle operation;
• keeps browser target/session IDs ephemeral and preserves exact persisted ChatGPT conversation identity;
• reopens only the saved conversation after target loss and checks exact URL identity before prompt mutation;
• keeps browser-control, signed-out, app-binding, conversation-drift, and peer-identity failures distinct;
• preserves OUTCOME_UNKNOWN != retry permission and does not add automatic transport fallback;
• persists the authenticated MCP peer fingerprint separately from the transport conversation fingerprint after bootstrap;
• keeps legacy managed CDP and optional OpenCLI compatibility paths intact.

Exact Candidate

• base: c40873c1ff37f4fb93b46b88028a5aebe63030c1
• head: 4d1c822e43851b43298386b0ba0a728fd7208a2e
• tree: 881ba9da8eee6831591d7509135e7224a780993e
• changed paths: 3
• deletions: 0
• diff: 992 insertions / 39 deletions

The final Candidate tree is byte-identical to the earlier locally verified Wave 3 Candidate tree; it was rematerialized through the Core-bound Candidate integration path so publication provenance stayed valid.

Verification

Exact-head local evidence:

• src/chat-swarm-runtime.test.ts: 36/36 PASS
• npm run typecheck: PASS
• npm run build: PASS; build identity devspace-1.0.7-4d1c822e
• full npm test: PASS (exit 0)
• git diff --check: PASS
• remote branch readback: exact head 4d1c822e43851b43298386b0ba0a728fd7208a2e

Hostile controls include malformed/missing DevToolsActivePort, endpoint rotation, exact-target isolation, lost target recovery, browser disconnect/ack loss with no resend, cross-session response rejection, conversation URL drift, signed-out classification, UNKNOWN/DISABLED/STALE app binding, durable binding reason retention, and authenticated-peer bootstrap continuity.

Claim boundary

This is G1 source Candidate evidence only. It does not claim installed-build/native Chrome authorization, exact deployed runtime, G2 zero-touch ensure(3), G3 targeted execution, G4 recovery, G5 scaling, G6 cold reconstruction, release, or production acceptance.

Current #117 ceiling remains:
MACOS_ZERO_TOUCH_CHATGPT_WORKER_RUNTIME_NOT_YET_PROVEN.