fix(host): BakedGraphProcessor survives in-place buffers + resets node state on prepare

[shipyard-local]

Two correctness fixes for baked-graph plugins, both found via a downstream
consumer but affecting any Pulp plugin built on BakedGraphProcessor:

1. In-place (aliased) host buffers no longer produce silence. Hosts like
   Logic (AUv2, some AUv3) hand process() input and output views over the
   SAME memory. process_routed() zeroes the main output bus before its
   AudioInput gather reads the input bus, so the zero destroyed the aliased
   input and the plugin emitted total silence. process() now detects any
   input-channel/output-channel overlap and reads the input from a scratch
   copy sized in prepare() — the audio thread does only pointer compares and
   copy_n, no allocation. Handles mono, multi-channel, and differing in/out
   channel counts.

2. prepare() re-inits stateful Custom-node DSP state. bake() captured only
   the opaque process callback, so a re-prepare rebuilt the routing snapshot
   and buffer pool but never re-ran the custom instance's prepare/reset —
   stale state (e.g. a delay line's contents) recirculated into the fresh
   stream, violating the header's documented starts-from-zero contract.
   bake() now also captures per-node CustomNodeLifecycle closures (the
   type's prepare/reset bound to the instance) and prepare() runs them:
   prepare at the host's REAL rate/block (load_baked previously left
   instances prepared at its nominal 48k/512), then reset. Mirrors
   SignalGraph::prepare()'s own instance step.

Both fixes ship with fail-without-fix-verified tests in
test_baked_graph_processor_parity.cpp: aliased mono/stereo blocks must be
the processed signal (not silence, and allocation-free under the RT probe),
and a silent block after re-prepare must carry no residue from a stateful
delay node.

Co-Authored-By: Claude Opus 4.8 (1M context) noreply@anthropic.com
Claude-Session: https://claude.ai/code/session_015tUppDEybTgFDxS5BGKBWV

---

🔎 Provenance

Agent	claude
Machine	m5
Tab	Analyze Pulp for AI plugin builder capabilities
Directory	~/Code/pulp-baked-fix
Session	14ef2f39-9113-4e61-bd8b-8faab97cab00

Resume

claude --resume 14ef2f39-9113-4e61-bd8b-8faab97cab00

Jump to this tab

cmux surface focus BD0A704A-23E0-4F9B-88CC-25BD1ACDAFEA

Relaunch (any agent)

cmux surface resume get --surface BD0A704A-23E0-4F9B-88CC-25BD1ACDAFEA

Restore URL — https://claude.ai/code/session_015tUppDEybTgFDxS5BGKBWV

_{stamped 2026-07-20 20:33 UTC}