feat(mcp): expose selected environment preferences

[juliusmarminge]

Part 10/16 of the shared-core and MCP stack. Based on #10559. Next: #10561.

Expose server identity and selected preferences, and update that allowlist through ServerSettingsService so ordinary persistence and client notifications are reused.

Updates require a live full-access/default caller under the existing ThreadCommandExecutor. Provider configuration, secrets and admin controls are not exposed. No new settings store or lock service.

MCP-only rebuild of #8726, #8728, preserving attribution to Julius Marminge's original work. Original branches remain available for separate service follow-ups.

Validation: The composed stack passes 94 tests across 12 focused files, including shared core MCP and real MCP/V2 integration, attachment intake, project RPC/service contracts, and client model command selection. Server/contracts/shared/client-runtime typechecks and targeted format/lint/diff checks pass. New behavior coverage lives with the shared operation; no per-tool mock suite was added. Current-head CI is shown below.

Layer size: 7 files, +185/-1. No domain-service production implementation or documentation files change in this MCP layer.

Prepared with Codex in the OpenAI agent runtime.

[github-actions]

Thread transfer impact

⚠️ The latest CI run did not produce a thread transfer result for d971e17.

This comment will update automatically after the next completed run.

[macroscopeapp]

Approvability

Verdict: Not approved

Macroscope's review found this PR not approvable — This PR adds and registers production MCP tools, including a write operation that persists environment-wide preferences and notifies connected clients, affecting subsequent server behavior. The capability is bounded and tested, but its new cross-component workflow and externally observable settings mutation warrant human review.

No code changes detected at d971e17. Prior analysis still applies.

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