feat(cua): attach the managed Cua Driver to every provider session

[juliusmarminge]

With the driver running (previous layer), every provider now gets it as a stdio MCP server named cua-driver:

Provider	How
Claude	SDK mcpServers; the query reopens when the set changes
Codex	thread mcp_servers, unless the user's merged Codex config already defines cua-driver (read once per directory with config/read); theirs wins
Cursor	SDK mcpServers
Grok, Antigravity, Devin, ACP registry	ACP mcpServers, in both stdio and MCP-over-ACP lists
OpenCode 1.x	mcp.add; the prompt mentions it only if the add succeeded
OpenCode 2	per-thread, per-directory registration with permission rules, like its t3-code server
Pi	Pi has no MCP client, so T3's Pi extension bridges the stdio server and passes screenshots through as images

Sessions with the driver get a short <computer_use> block: keep input in the background, escalate to foreground only when a background action did not land, and leave the desktop as found.

#15006 skipped Codex, OpenCode 2, and Pi. #10899 only attached Codex. This covers all of them.

#15006 also ran a per-thread proxy so T3 could end Cua's session at every turn end. This stack drops it: Stop still ends the provider's turn, and Cua's own idle timeout hides the agent cursor.

Verification

• Focused tests: Claude and Codex attachment, user-config precedence in Codex, the <computer_use> block, and the existing Claude, Codex, Cursor, ACP, Grok, OpenCode, OpenCode 2, Pi, and session-manager suites (687 tests).
• Checked by hand: Pi's stdio bridge against the real 0.34 driver lists 58 tools, calls list_apps, and reconnects after the driver exits.

Built with Claude Opus 5.5 in T3 Code, through the Claude Code harness.

🤖 Generated with Claude Code

[github-actions]

Thread transfer impact

✅ Thread transfer remains within every enforced ceiling.

ℹ️ No successful main baseline artifact is available yet. This run establishes the initial measurement.

Provider	Metric	Main baseline	This PR	Impact	PR ceiling
Codex	Total thread wire	—	5.0 KiB	—	6.8 KiB	✅
Codex	Thread snapshot wire	—	3.8 KiB	—	4.9 KiB	✅
Codex	Live turn WebSocket wire	—	1.2 KiB	—	2.0 KiB	✅
Codex	Live turn WebSocket decoded	—	20.9 KiB	—	29.3 KiB	✅
Codex	Live turn messages	—	2	—	8	✅
Claude	Total thread wire	—	5.0 KiB	—	6.8 KiB	✅
Claude	Thread snapshot wire	—	3.8 KiB	—	4.9 KiB	✅
Claude	Live turn WebSocket wire	—	1.2 KiB	—	2.0 KiB	✅
Claude	Live turn WebSocket decoded	—	21.2 KiB	—	29.3 KiB	✅
Claude	Live turn messages	—	2	—	8	✅

Baseline: unavailable · PR result: 79285b2 · Source CI: success

Scenario and decoded snapshot size

10 historical turns, 5 command tools per turn, 878.9 KiB retained MCP result per historical turn, and a 1.05 MiB retained result in the measured turn.

• Codex decoded thread snapshot: 108.5 KiB
• Claude decoded thread snapshot: 108.8 KiB

Updated in place by a trusted workflow. PR artifacts are strictly validated and never executed.