Routing v0.4: stale reference cleanup and typed/legacy parity matrix

[sigilabcodex]

Summary

This PR advances the v0.4 routing consolidation work in two compatibility-first phases:

1. Adds a confirmed cleanup flow for stale routing references.
2. Adds an executable typed/legacy routing compatibility matrix.

The PR intentionally does not migrate routing ownership, remove legacy routing, change the patch schema, or make Patch.routes the sole runtime authority.

Phase 3 — confirmed stale routing cleanup

Adds a user-confirmed cleanup action for routing references whose module or bus endpoint no longer exists.

Covered representations:

• legacy triggerSource
• legacy target-owned modulations
• legacy audio connections
• typed Patch.routes

Safety constraints:

• opening the routing inspector remains read-only;
• cleanup requires explicit confirmation;
• cancellation causes no mutation;
• valid references are preserved;
• cleanup is deterministic and idempotent;
• unrelated validation warnings are not automatically removed;
• legacy routing support and schema version remain unchanged.

Phase 4 — typed/legacy parity characterization

Adds docs/routing-compatibility-matrix.md and executable characterization tests covering:

• legacy, typed, and hybrid event routing;
• partial typed adoption;
• multiple event sources targeting one sound;
• legacy, typed, and hybrid modulation routing;
• legacy, typed, and hybrid audio routing;
• missing and unsupported bus endpoints;
• compiler, inspector, scheduler, modulation-runtime, and audio-runtime divergence.

Important documented findings:

• compileRoutingGraph() is still a normalizer/read model rather than the sole runtime authority;
• scheduler event resolution uses compiled routes first, then legacy triggerSource fallback;
• typed modulation is visible in the graph, but runtime modulation still reads legacy target-owned modulations;
• typed audio is compiled into connection-like records and then validated through the legacy connection validator;
• the inspector follows compiled graph state and may differ from scheduler-effective fallback behavior.

Validation

• npm run typecheck — passed
• npm test — passed, 164 tests
• npm run build — passed

Scope

This PR is intentionally limited to safe cleanup, characterization tests, and documentation. The next recommended step is an event-domain read resolver that can report both compiler-canonical and scheduler-effective sources before any ownership or runtime behavior is changed.