Seperating the sequencer into multiple widgets.

docs/ROADMAP.md

@@ -3656,6 +3656,55 @@ and inspection of the actual [audio envelope capture](../screenshots/audio-veloc
 
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+## Phase 111 — Sequencer Master and Child Widgets
+
+### Goal
+
+Split the sequencer GUI into focused components. Keep `SequencerWidget` as the
+master with real nested FLTK track, header, clip, velocity and ruler widgets,
+preserving current editing behavior, the C domain boundary and saved projects.
+
+### Tasks and acceptance criteria
+
+- [x] Make the master own ruler and track groups; each track owns its header,
+      instrument selector, clip widgets and velocity lane through FLTK ownership.
+- [x] Move child drawing and local input into dedicated track/header, clip,
+      velocity and ruler implementation files. Keep shared coordinates, selection,
+      scrolling and cross-track gesture completion in the master.
+- [x] Extract editing commands/dialogs, instrument support and waveform caching
+      into separate source files and register them explicitly in CMake.
+- [x] Reconcile views by stable C IDs, preserving surviving track identity through
+      reorder/undo and moving clip views into the destination track hierarchy.
+- [x] Cancel gestures on project replacement and defer removed widget deletion
+      until event handlers can return; preserve instrument focus and shortcuts.
+- [x] Exercise real parent/child membership, cross-track movement, velocity edits,
+      undo/redo, removal and project replacement through GUI integration tests,
+      including FLTK window-level event dispatch.
+- [x] Update the architecture/component map, GUI guide, build guidance, README
+      and integration-test documentation.
+
+### Implementation status
+
+Implemented on 2026-11-06. The master now delegates track/header, clip, velocity
+and ruler drawing/input to child classes; commands and support code are separate
+translation units. See [the ownership and source map](ARCHITECTURE.md#sequencer-widget-ownership).
+FLTK owns the hierarchy; indexes and captured-gesture pointers are borrowed.
+Child views hold copied C metadata rather than pointers into project snapshots.
+Removed children are detached/hidden and deleted through FLTK's deferred queue.
+The master remains the single selection and edit/publication coordinator.
+
+No dependency, core API, persistence or intended visual/workflow change is
+introduced. Existing screenshots continue to describe the same interface.
+Validation: the warning-enabled CMake build succeeds, all 55 existing CTests
+pass, and the added `gui-sequencer` hierarchy/dispatched-gesture check passes.
+The final build's main GUI and focused hierarchy tests were also rerun successfully.
+The focused hierarchy/lifetime test passes Clang ASan/UBSan with leak detection
+disabled for the unsanitized system FLTK library. Both audio-envelope captures
+remain pixel-identical to the existing gallery. Physical hardware qualification
+is unaffected.
+
+---
+
 ## Recommended Execution Order
 
 Reorder the phases when the audit reveals a blocking dependency. Do not mark a