Fix Cursor ACP dynamic tools

[ymichael]

What was wrong

Cursor ACP applies its project MCP approval gate to client-supplied session MCP servers. ACP has no client permission round trip for that gate, so Cursor rejected the valid bb-bridge stdio config before spawning it. The same config-advertisement path exists before and after #1834, and the #1932 bootstrap fix remains valid; the missing Cursor approval was the separate root cause.

What changed

The ACP bridge now installs the exact bb-owned session MCP fingerprint in the Cursor project approval store before session/new, session/load, or session/fork. It limits the workaround to cursor-agent plus the bb-bridge config, preserves existing approvals, serializes concurrent updates, and removes approvals that bb installed when the session ends.

The MCP child also reports initialize back to the bridge, giving host-side diagnostics for both config construction and successful child startup. No server/host-daemon wire contract changed, so HOST_DAEMON_PROTOCOL_VERSION does not need a bump.

How you verified

Added fingerprint, approval-file preservation/concurrency, session-lifecycle, and MCP initialize diagnostic regressions. These expose the missing approval before the fix and pass afterward.

• pnpm exec turbo run test --filter=bb-plugin-provider-acp --force — 175 passed
• pnpm exec turbo run typecheck --filter=bb-plugin-provider-acp
• Isolated manual run against Cursor CLI 2026.06.19-20-24-33-653a7fb, with approval installed after ACP initialize and before session/new; Cursor spawned and initialized the MCP server

Fixes #2018

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