fix(mcp): stop notification tasks during manager shutdown

[BunsDev]

Summary

Stop MCP notification tasks when their manager is dropped or explicitly shut down, including quiet streams and resource delivery blocked by a full channel.

Context

• User request: recover the focused shutdown correction from the saved command/runtime worktree.
• Scope: MCP notification lifecycle only. The broader CLI/plugin/scheduler draft is archived separately.

Changes

• Add a sticky, idempotent shutdown signal that wakes idle polling and cancels blocked delivery.
• Retain the subscription registry during delivery without retaining the manager across an await, so manager destruction can signal shutdown.
• Add regression tests for idle-manager drop, explicit shutdown, and backpressure cancellation.
• The public subscription registry is now Arc<DashMap<...>>; existing in-repository call sites remain compatible. The protected engine CLI/environment/stream contract is unchanged.

Validation

All Cargo commands used the stable toolchain with CARGO_INCREMENTAL=0.

• git diff --check
• cargo fmt --all
• cargo test -p claurst-mcp: 55 passed
• cargo check --workspace (no warnings)
• cargo clippy --workspace --all-targets -- -D warnings
• cargo test --workspace: clean workspace-package rebuild, 2,132 passed, 7 ignored. An earlier shared-target run reused unrelated API/core test binaries and was discarded; workspace check, Clippy, and the full suite were rerun after cleaning all 12 local packages while preserving external dependencies.
• Idle-manager-drop regression timed out on the original implementation, then passed after the fix.
• Independent spec and quality review passed.
• Manual TUI checks: N/A, no TUI behavior or layout changes.

PR Readiness

• Diff is limited to one intended file.
• Generated files were not edited by hand.
• Lifecycle documentation is included with the new shutdown API.
• No secrets, credentials, local paths, or unrelated logs are included.
• Public Rust field ownership change is described above; no broader runtime changes are included.

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Project	Deployment	Actions	Updated
docs	Ready	Preview	Oct 13, 2026 1:31pm UTC