feat(mcp): resolve room-scoped servers for Copilot connections

[bandzalkin]

Rebased onto main d7ab3429cbdb (2026-10-15)

Rebased onto current main (after #709, #804, #789/#775, #796 and #802) as one commit; head 975b266822599f7d4938ace864597b8e4c31665b. #762 is closed (superseded by #709), so this is reimplemented directly on #709's retained ACP room: no parallel retirement/shutdown machinery. A setup abandoned by its last waiter is recorded on the room, so a callback that swallows cancellation cannot publish a session or hand its late result to the next turn; a turn that keeps waiting reuses the session its shared setup published. docs/acp.md documents resolve_mcp_servers in its own section, leaving the shared configuration paragraph untouched.

CHANGELOG.md edits are dropped: Release Please generates it.

Verified at the new head (macOS, Python 3.13): uv sync --all-packages --locked --extra dev, all pre-commit hooks, and the full pytest -q: 8613 passed, 738 skipped. Verification notes further down refer to the previous head.

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Summary

Resolve room-scoped external MCP servers for Copilot through the shared ACP initializer, preserving one owned snapshot and its cleanup boundary. Related: #709.

Changes

• Resolve a fresh MCP snapshot per initializer and preserve Band's endpoint, precedence and structurally redacted launch settings. The shared path also covers Cursor.
• Retain setup and runtime-close ownership through cancellation/teardown; refuse turns on a runtime held only for failed-close retry.
• Keep resolver documentation independent of native OMP migration.
• Update ACP configuration documentation and user-facing Unreleased entries.

Stack and merge order

No prerequisite; based on upstream d7ab3429cbdb5381b9ca572cf7eac210a8196052. Exact range: d7ab3429cbdb5381b9ca572cf7eac210a8196052..975b266822599f7d4938ace864597b8e4c31665b.

CI portability correction

The eager-host teardown regression now uses the existing conftest requires_eager_tasks/eager_tasks helpers. Python 3.11 explicitly skips that scheduling mode; 3.12/3.13 execute it. Product code and timeouts are unchanged. Test-only changelog entries were removed.

Testing

Prepared head differs from approved/tested b6d41cb8 only in CHANGELOG.md. At the tested head, managed Python 3.11/3.12/3.13 ACP resolver module: 50 passed / 1 eager-host skip; 51 passed; 51 passed. Fresh non-privileged Linux Python 3.11: 50 passed / 1 eager-host skip. All five static hooks passed freshly at the prepared head.
Historical pre-correction ACP/converter/shared-backend/conformance/Strands scope: 1843 passed, 69 skipped, 11 warnings at 626b87f1; not a new-head full-suite claim. Current source/index-delta stable patch ID: 4a909ddba317d3d3701f1cfba08bf2930e33ecfe, excluding only changelog/fork metadata. No new fork graph is claimed.
Local regressions are not native Copilot/Cursor or live-room receipts. Remote matrix and staged-package validation remain separate gates.

[bandzalkin]

Rebased onto current main (d7ab3429) at 975b26682259; the description's new first section lists the conflict resolutions and the verification at this head.