[astrobyte-dev]

P4 makes Studio a place to safely explore a groove: enter Jam, keep Bass and Kick, vary the remaining rhythms, compare ideas, shape the sound with semantic macros, and promote favorite clips into a Drop scene. All authored changes use the existing canonical project, revision, retry, Undo and storage contracts.

This draft is intentionally stacked on feat/p3.5b-capture-sampling at 63d99d0f61fc62f1430db8abebb60f540f90b164. Do not merge lower drafts or retarget this PR to main. P5 was not started.

• Adds seeded, source-aware variations/Chaos and authored Fill; persistent track/rhythm/sound/FX/motion and parameter constraints; seven semantic verbs with changed/kept summaries.
• Adds bounded Original/variation/favorite snapshots, canonical A/B/return/branch, scene clip promotion, quick starts, instrument bench pins and optional deterministic suggestions.
• Adds project macros and simple software assignment using stable Sound Lab semantic identities. Native offsets remain separate from base/automation/modulation. Locks preserve the macro contribution already being heard; free targets remain adjustable.
• Adds a bounded performance event notebook and structured MCP operations, plus persistence/recovery and real browser/MCP synchronization coverage.

Available validation on Ubuntu 24.04.4, Node 24.14.0 / npm 11.9.0: 374 passed, 3 Windows-only skips, 377 discovered (73 new P4 tests); production build and both typechecks passed. All eight browser journeys and the Linux runtime/lifecycle harness passed. Reviewed and refined screenshots at 1280/1440/1920; no horizontal overflow or browser errors. Existing tests remain preserved.

Deliberate limits: macros commit on gesture release and synth offsets affect new notes; scenes copy clips/clip automation while instruments, FX and macros remain shared; the runtime idea trail requires normal project Save for disk retention. The performance notebook preserves acknowledged order and scheduled scene cycles, with no automatic replay or arrangement conversion. Temporary browser-timed moment/stutter/drop events were not added.

Implementation complete does not mean native acceptance complete. P2.6 Windows desktop/audio; P3 native audio/timing and Windows; P3.5A native audio/timing/CPU and Windows; P3.5B native microphone/audio and Windows all remain pending. P4 also requires native audible/musical-quality, macro/timing/CPU and Windows acceptance. Ubuntu remains Level B — Runtime Safe. No audio/kernel/system packages changed.

Full architecture, tests, review fixes, limitations, screenshots and exact exit matrix: P4 completion report, validation JSON, task.