R0-2 — extract one deep HostedPlugin lifecycle/state seam

[masarray]

Parent: #56

Blocked by: #63 R0-1 — completed / GO; merged main bcddeb78e0b666d8ba2b4ae6d9ce355142181d5d

Purpose

Extract the proven helper-side one-VST3 lifecycle/state/process behavior into one deep protocol-neutral HostedPlugin seam while preserving Single Host behavior and keeping Single transport/orchestration outside the extracted object.

Fixed-point base for this thread: bcddeb78e0b666d8ba2b4ae6d9ce355142181d5d.

Vertical proof

One helper-side object owning one VST3 can be exercised independently of Single transport semantics while Single Host remains behaviorally equivalent.

Test first / characterization

Characterize and keep green:

• open/close lifecycle;
• protocol-neutral process behavior via the accepted ProcessBlockView seam;
• latency;
• component/controller state round-trip;
• supported restart/lifecycle behavior;
• helper-owned editor accessor ownership.

Reuse deterministic existing seams where already covered; add the smallest missing characterization needed to prove the extraction itself.

Implementation

• converge proven Vst3Engine responsibilities into a deep HostedPlugin seam;
• transport adapter remains outside;
• Single helper orchestration stays equivalent;
• no OBS-side state/recovery moves into HostedPlugin;
• keep Single protocol layout/version unchanged;
• do not change scanner, OBS Properties, installer or state-file naming for Rack needs.

Acceptance

• all mandatory Single lifecycle/state/latency/parameter/process-context/recovery/protocol regressions green;
• deterministic engine/process characterization remains green;
• Windows helper/module + scanner smoke green;
• supported OBS compatibility/package gates green on the exact final source head;
• representative real-machine Single smoke required by ADR-0004 remains green before merge;
• fixed-point Standards + Spec review has no unresolved findings.

Non-goals

• no Rack protocol/helper;
• no multi-plugin runtime;
• no R1-1 work;
• no generic plugin-format abstraction;
• no MIDI/graph ports;
• no scanner redesign;
• no graphical Rack implementation;
• no Single protocol redesign.

Thread rule

Stop after R0-2 acceptance/evidence. R1-1 must start in a fresh thread.

[masarray]

R0-2 pre-mutation fixed point

Exact main / R0-2 base is bcddeb78e0b666d8ba2b4ae6d9ce355142181d5d (tree 956e8b3a5720e8242ea2993263521a2bca7d9c51). Branch r0-2-hosted-plugin was created directly from that commit.

Repository authority read in mandatory order. R0-2 scope is only the deep one-VST3 extraction required by issue #66 / VST3_RACK_TICKETS.md:

• extract proven lifecycle/state/process ownership into protocol-neutral HostedPlugin;
• keep Single AudioSlot transport adapter outside HostedPlugin;
• preserve Single helper orchestration/observable behavior;
• keep protocol layout/version unchanged;
• no Rack protocol/helper, no multi-plugin runtime, no R1-1.

Implementation direction before mutation: retain Vst3Engine as a thin Single compatibility adapter around/in front of the extracted HostedPlugin, so the existing helper call graph remains equivalent. HostedPlugin must not include or depend on Single AudioSlot layout. Generic host bounds currently co-located in common/protocol.hpp will be split without changing their values or the serialized protocol layout.

Mandatory final gates remain: deterministic deep-object characterization + all named Single regressions, Windows helper/module/scanner smoke, supported OBS compatibility/package gate, Standards + Spec review, and representative real-machine Single smoke on the unchanged final candidate before merge.

[masarray]

R0-2 frozen exact-candidate checkpoint — automated gates PASS

Fixed-point base / current main: bcddeb78e0b666d8ba2b4ae6d9ce355142181d5d

Frozen R0-2 source candidate: 14ac1de41346c9fe1ace30f96bf1670c839da1f9
PR: #68

Exact-head automated evidence:

• R0-2 HostedPlugin Characterization S1: Full VST3 component/controller state persistence #9 — run 33177236012 — SUCCESS
• R0-1 Process Seam Characterization Prepare v0.4.1-rc.1 scanner/editor trial #20 — run 33177236019 — SUCCESS
• CI #385 — run 33177236014 — SUCCESS
• Compatibility Test Build #167 — run 33177236085 — SUCCESS

Compatibility artifact:

• ID 9688622098
• name OBS-Safe-VST3-Host-v0.4.1-stabilize-test5-windows-x64
• exact head 14ac1de41346c9fe1ace30f96bf1670c839da1f9
• outer SHA256 74f39d0f65bf53ccb2733f551c61b0aa1f73a25f35d6bd36f04830365fb4a99b
• Setup EXE SHA256 0b408bbbcb9b87b38ce75f5f798829bb5b888ead0d10506ea209aec836984f2b
• Portable ZIP SHA256 1717fe1aa15424f6e7d92244cc359fd281069ecc81e966c91ca538ccbeb6c3dd
• helper EXE SHA256 ae83ae9bdad8c5916a380afdc6dfd9cc27552fab991dd47320fbadce80605ee6
• module DLL SHA256 f70a327f89c33e312c731ec7c8e3e74453a2e1c42cdf26cd976ec9d57896e2ad
• scanner EXE SHA256 c6d89d34f5e2779256712651448a2ab7ba76ef83983921a343b18f8e3a9b283a

Standards + Spec review: PASS, no unresolved findings. HostedPlugin owns one-effect lifecycle/state/process through the qualified implementation core and exposes no Single/Rack shared-memory layout; its public process seam is ProcessBlockView only. No Rack protocol/helper, multi-plugin runtime, or R1-1 work is present. PR has no review threads and main has not drifted.

Remaining fail-closed gate before merge: representative real-machine Single smoke on this exact artifact:
A normal audio; B vendor editor open/hide/reopen; C exact state continuity through helper recreation; D dry fail-open during helper recovery.

Do not merge/close until all four are explicitly PASS on this exact candidate.