Close Rust maintenance plan with sustainable guardrails

[beiwei30]

What changes

Close the bounded Rust maintenance plan with a reproducible before/after report and narrow, non-pedantic guardrails for internal permission strings, raw nested options, and production tokio::spawn owners.

Also replace two load-sensitive fixed-time assumptions in WebSocket and MCP stdio tests with deterministic readiness/event synchronization. Production Rust behavior, public APIs, wire formats, fixtures, snapshots, and goldens are unchanged.

Verification

$ scripts/check.sh
✓ All checks passed. (PTY e2e run separately: scripts/check.sh --pty-e2e)
$ cargo clippy --workspace --all-targets -- -D warnings
Finished `dev` profile successfully
$ python3 scripts/audit-rust-maintenance.py --self-test
Ran 4 tests
OK
$ scripts/audit-rust-maintenance.py
✓ string-typed permission_mode boundaries: 6 reviewed occurrence(s)
✓ raw nested-option boundaries: 11 reviewed occurrence(s)
✓ production tokio::spawn owners: 55 spawn(s) across 35 reviewed owner anchor(s)
$ cargo test -p orbcode-tools skills::loader_tests::bounded_mcp_skill_discovery_timeout_does_not_cancel_stdio_request -- --exact
Passed in 10 consecutive runs
$ scripts/rust-maintenance-report.py # run twice
SHA-256 da48915927bcbed49f19d122de9fb65db4f38171051abf0f80ff10d31376e3fa for both byte-identical outputs

Compatibility

• No golden fixture under compat-fixtures/fixtures/ or tui/testdata/ changed.
• No TypeScript-CLI compatibility name was renamed; scripts/audit-brand.sh passes.
• The public API surface is unchanged; scripts/audit-public-surface.sh passes.
• The test-only readiness and synchronization changes are covered by their affected crate tests.

Notes for the reviewer

The checked-in allow-list records complete, bounded best-effort, or named deferred lifecycle dispositions for every current production spawn owner. Remaining numeric, mechanical, error-source, API, and representation findings are explicitly deferred in the closeout report; this PR does not claim pedantic zero.

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