Phase 3 / M6: Classify patch changes and plan symbolic state migration

Objective

Diff patch generations and select safe no-op, in-place, hard-swap, or crossfade transition plans while preserving compatible symbolic state.

Add compatibility fingerprints distinct from full fingerprints.
Classify no-change, control-state, control-schema-compatible, DSP-compatible, and DSP-incompatible changes.
Implement transition plans and validate explicit strategy/crossfade overrides.
Elide identical updates and use in-place updates only where state layout is proven compatible.
Plan control, automation, and bus migration by instrument/parameter ID and scope—not binding index.
Handle range/scope changes, removed parameters, invalid automation, and diagnostics according to policy.
Keep the last known-good engine/state if preparation or migration fails.
Add classifier, planner, migration, unsafe-override, and failure tests/fuzzing.

Fixtures classify every change class deterministically.
Identical patches are elided and compatible updates preserve valid controls/mappings.
Incompatible changes select crossfade by default; failed plans do not corrupt the registry or running engine.

Spec: phase-3.md §§16–17, 19, 30, 32, 35, 40 (Milestone 6), 42.