feat(studio): revamps Studio + improves code quality (#2291)

* feat(studio): glue API coexistence layer for the NLE swap

What: extends 21 glue files so the OLD timeline/canvas engine and the NEW
NLE components type-check side by side: playerStore (multi-select setters,
zoom pin, snap toggle, non-reactive scale scratch), drag-state types gain
optional NLE fields, timelineLayout/timelineAssetDrop/timelineEditingHelpers/
timelineEditing/timelineElementHelpers/studioHelpers/assetHelpers gain the
NLE exports, DomEditOverlay + gestures + AssetContextMenu + Timeline props
gain optional callbacks/params, contexts gain *Optional hooks, and
TimelineEditCallbacks.onMoveElements becomes a bivariant method accepting
both engines' change shapes. patchDocumentRootDuration's test rides along.

Why: this is the keystone that dissolves the old "welded glue" problem —
every symbol the NLE components need is ADDED next to what the old engine
still uses, so the engine components and the swaps can land as separate
reviewable PRs.

How: 15 authored intermediate files (main content + additive symbols; no
behavior changes — new fields optional, new callbacks unused until wired)
plus 6 files whose final content is already purely additive. New exports
without consumers yet carry TEMP(studio-dnd) ignoreExports entries, removed
by the app-shell swap.

Test plan: tsc --noEmit in studio + studio-server (verifies BOTH engines
compile); bunx vitest run (full suite green incl. the 6 new
patchDocumentRootDuration tests); fallow audit clean.

* feat(studio): timeline interaction hooks and lanes component (unwired)

What: the timeline-side wiring layer, unwired: TimelineLanes (the lane
renderer driving drag/resize/marquee), timelineMarquee (+tests),
useTimelineStackingSync, useTimelineGeometry, useTimelineEditPinning,
useTimelineEditingDrops.

Why: everything between the pure drag math and <Timeline> itself; the
timeline-glue swap PR then only rewires Timeline/TimelineCanvas onto these.

How: new files, tsc-clean against the coexistence layer. Unwired components
carry TEMP(studio-dnd) entry registrations, removed at the app-shell swap.

Test plan: bunx vitest run timelineMarquee.test.ts; tsc --noEmit; fallow
audit clean.

* feat(studio): NLE shell assembly (unwired)

What: EditorShell (the full editor layout replacing NLELayout +
StudioPreviewArea), TimelinePane (timeline host with sub-comp rebasing) and
useTimelineEditCallbacks (the callback bag bridging store edits to the
timeline), all unwired.

Why: the shell that App swaps to in the final step; reviewing it standalone
keeps that swap PR small.

How: new files against the coexistence layer; TEMP(studio-dnd) entries
until App mounts EditorShell in the app-shell swap.

Test plan: tsc --noEmit; bunx vitest run (suite unchanged); fallow audit
clean.

* feat(studio): timeline glue swap — Timeline/TimelineCanvas onto the NLE engine

What: flips the timeline glue to its final form (23 files): Timeline and
TimelineCanvas rebuilt on TimelineLanes/TimelineOverlays, useTimelineClipDrag
drives preview/commit through the new drag engine, range selection goes
multi-select, playback loop moves to useTimelinePlayerLoop. Deletes the 9
old-engine files this orphans (group drag, marquee selection, snap targets,
layer gutter, selection overlays + their suites) — each is compile- or
gate-forced by this swap, verified by probe.

Why: second swap step; timeline-only, canvas and App untouched.

How: modified files to final content + forced deletions.
playerStore/timelineEditing/timelineCallbacks stay at their coexistence
form until the app swap (the old App still runs on them).

Test plan: tsc --noEmit; bunx vitest run (full suite); fallow audit clean.

* feat(studio): clip thumbnail modules

What: ImageThumbnail (+tests) and thumbnailUtils (+tests) — frame decode
with SVG/AVIF format fallbacks and rounded-corner clipping — plus
VideoThumbnail updates.

Why: the decode layer for timeline clip thumbnails, ahead of the visual
refresh that renders them.

How: new modules + one modified file; purely presentational.

Test plan: bunx vitest run on both test files; tsc --noEmit; fallow audit
clean.

* feat(studio): assets/blocks panel behaviors + preview helpers

What: blocks tab install flow, right-panel and global drag-overlay polish,
music beat analysis and clip-content rendering hooks, and the
preview-helper utilities backing asset preview.

Why: completes the studio NLE stack on top of the visual refresh.

How: modified files only (kept as one PR: splitting further would produce
sub-150-LOC fragments of interdependent panel glue).

Test plan: bunx vitest run studioPreviewHelpers/studioUrlState suites; tsc
--noEmit; fallow audit clean.

* fix(studio): restore timeline playback loop

* fix(studio): restore missing GSAP helpers module

* refactor(studio): split timeline GSAP helpers

* style(studio): keep timeline helper under size limit

* fix(studio): restore timeline overlays module

* fix(studio): remove stale GSAP import

* fix(studio): restore canonical timeline dependencies

* style(studio): format restored timeline helpers

* style(studio): satisfy helper line limit

* fix(studio): repair rebuilt timeline integration

* feat(studio): complete rebuilt NLE cutover

* fix(studio): guard project and timeline race boundaries

* fix(studio): preserve graded resize and crop geometry

* fix(studio): log resize/rotate commit failures, move anchor accumulator to resize-local

* fix(studio): treat duration-0 tweens as static holds and settle resize position before persist

Instant holds (to()/fromTo() with duration 0) were classified as animated
tweens by every commit route, so resizing or rotating them converted the
hold into a corrupt duration-0 keyframes tween (new value at 0%, old at
100%) that GSAP drops; panel edits appended a losing set. A shared
isInstantHold() now routes them through the static replace-in-place path,
and percentage math guards zero-duration windows.

Separately, anchored-corner resizes painted 3-5 frames at the new size but
old position while the offset persist round-tripped the server. The commit
path now applies the corrected GSAP position synchronously before awaiting
the offset persist, mirroring the scale route's settle.

* feat(studio): gesture-transaction seam with commit observability

Introduce runGestureTransaction — one owner for a gesture commit's
settle -> persist -> record lifecycle. It settles the live DOM
synchronously before any async persist, folds every mutation into one
undo entry via a per-transaction coalesceKey, restores pre-gesture state
exactly once on failure, and asserts (dev console) + reports (PostHog:
commit_transaction / commit_invariant_violation / commit_transaction_failed)
that a persist never changes pixels. The box-size resize path is migrated
onto it; the ad hoc per-route coalesceKey/reload handling is removed.

Extract the resize draft-rect math into resizeDraft.ts to keep the
gesture-handler file under the size cap.

Also: keep url_hash telemetry to the route slug only (drop the query
string, which carried the user's selected element id/selector), and gate
the [hf-resize] diagnostics behind localStorage hf-resize-debug so they
ship as opt-in tracing rather than console noise.

* fix(studio): transaction owns the undo label

The coalesced history entry took the last sub-mutation's label, so a
resize surfaced as "Move layer" (the offset persist) in undo/redo. The
seam now stamps tx.label on every wrapped mutation, so the folded entry
reads as the gesture.

* fix(studio): atomic static size/position commits (no data loss)

Static resize/position holds updated an existing set via delete+add — two
undo entries, and a delete that succeeded before a failed add lost the
hold on disk. Use one in-place update-properties mutation when a set
exists (one undo entry, no partial-failure window). The keyframed-hold
heal that can't be expressed as a property update now adds before it
deletes, so any single failure leaves a recoverable duplicate, never a
lost hold. Transaction-owned commits are tracked via a WeakSet so the
heal path never double-wraps an already-wrapped gesture.

* fix(core): restore timed-clip visibility after a forced timeline rebind

__hfForceTimelineRebind force-rendered the re-registered timeline but never
re-ran the per-[data-start] visibility pass, so after undo or soft reload
every clip rendered regardless of its time window until a full page reload.
Extract the visibility loop into syncTimedElementVisibility and call it from
both syncMediaForCurrentState (unchanged) and the rebind.

* fix(studio): atomic z-order/keyframe/split commits, one undo entry each

Three edit-commit paths hardened onto the one-transaction invariant:

- Z-order reorder (useElementLifecycleOps): N per-element writes now fold
  into one undo entry (coalesceMs Infinity) and, on a failed persist,
  restore already-written files to disk so no partial reorder survives.
- Enable-keyframes (useEnableKeyframes/useGsapKeyframeOps): the intermediate
  convert phase no longer full-reloads the preview (skipReload), killing the
  black-flash remount; convert + edit share one coalesce key = one undo entry.
- Razor split-all (useRazorSplit): snapshot before the batch and restore on
  any failure, so a mid-batch error never leaves un-revertable partial splits.

Shared file-history helpers (RecordEditInput, DomEditCommitBaseParams,
readProjectFileContent, restoreFilesToOriginal) dedupe the rollback/commit
logic across these paths. Commit options thread as one partial object rather
than field-by-field. Test setup extracted into colocated helpers.

* fix(studio): fold multi-step edits into one undo entry; guard text revert

- Gesture recording (useGestureCommit): the per-property-group commits now
  share one coalesce key and only the last reloads, so a recording is one
  undo entry and one preview reload instead of up to four.
- Delete selected keyframes (deleteSelectedKeyframes, split out of
  timelineEditingHelpers): N removals fold into one coalesced undo entry
  with a single reload.
- Text-field commit (useDomEditTextCommits): commitDomTextFields now uses
  the same version-guarded revert as handleDomTextCommit, so a stale failed
  commit can no longer stomp a newer successful one.

* feat(studio): batch a gesture's mutations into one atomic server write

A transaction that emits N mutations previously did N sequential POSTs,
each rewriting the file and soft-reloading — the root of the multi-phase
persist window. Add a gsap-mutations-batch endpoint that validates every
mutation up front, applies them in one in-memory rewrite chain, and writes
the file once (all-or-nothing: an invalid entry rejects the whole batch,
no partial write). The seam buffers a transaction's commits and, when more
than one targets the same file, dispatches a single batch — one write, one
history entry, one reload. The batch capability rides on the existing
commit-function reference; no option fields are threaded through callers.

* fix(studio): soften off-canvas indicator outline to 30% opacity

The dashed off-canvas selection outline at 60% was noisy with many
protruding elements on screen; drop the resting opacity to 30% (hover
still restores full opacity so it stays discoverable).

* fix(studio): drop off-canvas indicator outline to 10% opacity

Follow-up to the 30% softening — 10% resting opacity reads much calmer
with many protruding elements; hover still restores full opacity.

* fix(studio): gate [hf-commit] console traces to dev only

The start/settled/persisted/restore lifecycle traces logged on every
gesture commit in all environments — console noise for end users. Route
them through a dev-only traceCommit helper (matching the pixel-violation
error's existing DEV gate). The commit_* PostHog events stay always on;
they are the production observability, the console lines are a dev aid.

* fix(studio): count actual reloads, not softReload requests, in commit telemetry

A resize's size and offset persists both request softReload; the seam
counted each request, so a batched gesture reported reload_count 2 even
though the batch is one write and one reload. Compute the count from what
dispatchBufferedCommits actually did — one for a batch, the request count
for the sequential fallback.

* fix(studio): rotate hover + off-canvas overlays with the element; flicker-free crop

- Hover overlay applied the element's rotation only to the selection chrome,
  not the hover box; it now rotates about center like the selection, via a
  shared orientedGroupAwareOverlayRect router (one owner for rotation-aware
  overlay geometry across hover/selection/off-canvas).
- Off-canvas indicator was axis-aligned; it now rotates with the element and
  inverse-rotates the canvas-exclusion clip into the element's local frame,
  so the protruding-sliver clip stays correct for rotated elements.
- Crop commit re-lifted the element only in the commit's .then(), so one
  frame painted the cropped state (the flicker). Re-lift synchronously right
  after onStyleCommit (which applies the clip before its first await), so the
  cropped state never paints; the persisted file value is unchanged.

* fix(studio): address code-review findings across the commit-hardening campaign

Correctness (would ship green, bite under latency):
- Enable-keyframes phase 2 now carries coalesceMs: Infinity, so the convert
  folds into one undo entry instead of splitting past the 300ms default.
- The SDK keyframe persist path forwards coalesceMs (CutoverOptions gains the
  field); multi-keyframe delete and convert coalesce correctly when SDK-routed.
- Razor split-all's rollback is guarded so a failing restore can't swallow the
  error toast that tells the user the split failed.

Simplification (single source of truth / no dead flexibility):
- Decompose resolveResizeDraftRect (drops a fallow-ignore suppression).
- Delegate the third readProjectFileContent copy to the shared helper.
- Inline setPatchFromUpdateProperties (its only caller passes one mutation).
- One toSdkPersistOptions translates gesture overrides to SDK options.
- Bundle the reorder-rollback deps into one object (was 7-9 positional args).
- Dedupe the 'last group reloads' ternary; type gesture options as
  CommitMutationOptions; drop a Map+array wrapper around a single write.

* feat(studio): atomic z-order reorder via batch patch-element endpoint

Z-order reorder issued N per-element inline-style patches (one server
write each), so a mid-chain failure could leave a partial reorder on disk.
Add a patch-elements-batch endpoint that validates every patch, folds them
over the file in one in-memory rewrite, and writes once (all-or-nothing;
unsafe input rejects with no write). The reorder now sends one batch per
source file and records one undo entry. Because a failed atomic write
persists nothing, the interim disk-write-back rollback (restoreReorderedFile
/ restoreFulfilledReorderFiles / ReorderRollbackDeps) is deleted — failure
rolls back only live DOM/store state. Closes the last disk-atomicity gap.

* fix(studio): razor-split undo no longer silently no-ops

The split clone was written to disk without a data-hf-id, so the split
endpoint recorded that unstamped HTML as the undo entry's afterHash. The
next reloadPreview() ran the preview route's ensureHfIds write-back, which
minted a fresh id and persisted DIFFERENT bytes — so at undo time the disk
hash no longer matched afterHash and editHistory's content-mismatch guard
silently refused the undo (no write, no network, no error). Stamp the split
output via ensureHfIds in splitElementInHtml before it is written/returned,
so the preview write-back is a no-op and the recorded afterHash always
equals the final on-disk bytes. Fixes at the source rather than relaxing the
mismatch guard. Corrects the stale comment that credited forceReloadSdkSession.

* feat(studio): closed-hand grab cursor on the rotate handle

The rotate handle used the default arrow cursor; show a grabbing
(closed-hand) cursor on hover to signal it's grabbed and dragged to rotate.

* fix(studio): dropping a dragged element over another no longer selects it

A moved drag's release fired the box click, which re-selected whatever now
sat under the pointer via the hover cache — so dropping an element over a
higher-z one selected the drop target instead of keeping the dragged
element selected. The drag-move branch now suppresses the next box click,
mirroring the resize branch.

* fix(studio): group drag is one undo entry, not one per element

Dragging a multi-selected group committed each member's position write as
its own undo entry, so reverting took N Cmd+Z presses. Force a shared
coalesceKey (infinite window) across every member's commit so they fold
into a single undo entry, like the other multi-step commit paths.

* fix(studio): undo of a split no longer leaves a ghost clip in the timeline

The file and the composition iframe revert correctly on undo, but the
timeline panel kept a ghost node for the split clone. The element-merge
that repopulates the timeline preserves elements the fresh scan dropped —
intended for enriched sub-composition children a bare DOM re-scan misses,
but it also preserved a genuinely-removed TOP-LEVEL element (the split
clone after undo), leaving a phantom clip. Restrict the preserve to
elements with a compositionSrc (the enriched sub-comp children); a
top-level element missing from the fresh scan was truly removed.

---------

Co-authored-by: ukimsanov <ular.kimsanov@heygen.com>

packages/studio/src/player/components/timelineDragDrop.ts

@@ -1,23 +1,50 @@
 import { useCallback, useState, type RefObject } from "react";
 import { TIMELINE_ASSET_MIME, TIMELINE_BLOCK_MIME } from "../../utils/timelineAssetDrop";
+import { usePlayerStore } from "../store/playerStore";
 import { TRACK_H, resolveTimelineAssetDrop } from "./timelineLayout";
 import type { TimelineDropCallbacks } from "./timelineCallbacks";
-import type { StackingTimelineLayer, TimelineLayerId } from "./timelineTrackOrder";
 
 interface UseTimelineAssetDropOptions extends TimelineDropCallbacks {
   scrollRef: RefObject<HTMLDivElement | null>;
   ppsRef: RefObject<number>;
   durationRef: RefObject<number>;
-  trackOrderRef: RefObject<TimelineLayerId[]>;
-  timelineLayersRef: RefObject<StackingTimelineLayer[]>;
+  trackOrderRef: RefObject<number[]>;
 }
 
+type TimelinePlacement = { start: number; track: number };
+
+/**
+ * Parse a JSON drag payload and, if it yields a value, forward it to the drop
+ * callback. Malformed payloads are ignored. Shared by the asset + block paths so
+ * the parse/guard/dispatch shape lives in one place.
+ */
+function applyJsonDropPayload(
+  raw: string,
+  pick: (parsed: Record<string, string | undefined>) => string | undefined,
+  apply: (value: string, placement: TimelinePlacement) => void,
+  placement: TimelinePlacement,
+): void {
+  try {
+    const value = pick(JSON.parse(raw) as Record<string, string | undefined>);
+    if (value) apply(value, placement);
+  } catch {
+    /* ignore malformed drag payloads */
+  }
+}
+
+/**
+ * Dropping an asset/file/block onto the timeline places it at the PLAYHEAD —
+ * start is the current playhead time, only the track comes from the drop y.
+ * Deliberate product choice (user preference, 2026-07-09): every add lands at
+ * the playhead regardless of drop x, like CapCut's add-to-timeline. External
+ * OS file drops and internal asset drops share this same placement path, so
+ * both land identically.
+ */
 export function useTimelineAssetDrop({
   scrollRef,
   ppsRef,
   durationRef,
   trackOrderRef,
-  timelineLayersRef,
   onFileDrop,
   onAssetDrop,
   onBlockDrop,
@@ -25,83 +52,65 @@ export function useTimelineAssetDrop({
   const [isDragOver, setIsDragOver] = useState(false);
 
   const handleAssetDragOver = useCallback((e: React.DragEvent) => {
-    const hasFiles = e.dataTransfer.files.length > 0;
     const types = Array.from(e.dataTransfer.types);
+    const hasFiles = types.includes("Files");
     const hasAsset = types.includes(TIMELINE_ASSET_MIME);
     const hasBlock = types.includes(TIMELINE_BLOCK_MIME);
     if (!hasFiles && !hasAsset && !hasBlock) return;
     e.preventDefault();
-    if (hasAsset || hasBlock) e.dataTransfer.dropEffect = "copy";
+    e.dataTransfer.dropEffect = "copy";
     setIsDragOver(true);
   }, []);
 
+  const clearDropPreview = useCallback(() => setIsDragOver(false), []);
+
+  const resolveDropPlacement = useCallback(
+    (clientX: number, clientY: number): TimelinePlacement => {
+      const scroll = scrollRef.current;
+      const rect = scroll?.getBoundingClientRect();
+      // Track comes from the vertical drop position; start is the playhead.
+      const { track } = resolveTimelineAssetDrop(
+        {
+          rectLeft: rect?.left ?? 0,
+          rectTop: rect?.top ?? 0,
+          scrollLeft: scroll?.scrollLeft ?? 0,
+          scrollTop: scroll?.scrollTop ?? 0,
+          pixelsPerSecond: ppsRef.current,
+          duration: durationRef.current,
+          trackHeight: TRACK_H,
+          trackOrder: trackOrderRef.current,
+        },
+        clientX,
+        clientY,
+      );
+      const start = Math.max(0, usePlayerStore.getState().currentTime);
+      return { start, track };
+    },
+    [scrollRef, ppsRef, durationRef, trackOrderRef],
+  );
+
   const handleAssetDrop = useCallback(
-    // fallow-ignore-next-line complexity
     (e: React.DragEvent) => {
       e.preventDefault();
       setIsDragOver(false);
-      const scroll = scrollRef.current;
-      const rect = scroll?.getBoundingClientRect();
-      const layerById = new Map(timelineLayersRef.current.map((layer) => [layer.id, layer]));
-      const trackOrder = trackOrderRef.current
-        .map((id) => layerById.get(id)?.placementTrack)
-        .filter((track): track is number => track != null);
-      const dropInput = {
-        rectLeft: rect?.left ?? 0,
-        rectTop: rect?.top ?? 0,
-        scrollLeft: scroll?.scrollLeft ?? 0,
-        scrollTop: scroll?.scrollTop ?? 0,
-        pixelsPerSecond: ppsRef.current,
-        duration: durationRef.current,
-        trackHeight: TRACK_H,
-        trackOrder,
-      };
+      const placement = resolveDropPlacement(e.clientX, e.clientY);
+
       if (onFileDrop && e.dataTransfer.files.length > 0) {
-        void onFileDrop(
-          Array.from(e.dataTransfer.files),
-          scroll && rect ? resolveTimelineAssetDrop(dropInput, e.clientX, e.clientY) : undefined,
-        );
+        void onFileDrop(Array.from(e.dataTransfer.files), placement);
         return;
       }
       const assetPayload = e.dataTransfer.getData(TIMELINE_ASSET_MIME);
-      if (assetPayload && onAssetDrop && scroll && rect) {
-        try {
-          const parsed = JSON.parse(assetPayload) as { path?: string };
-          if (parsed.path)
-            void onAssetDrop(
-              parsed.path,
-              resolveTimelineAssetDrop(dropInput, e.clientX, e.clientY),
-            );
-        } catch {
-          /* ignore malformed drag payloads */
-        }
+      if (assetPayload && onAssetDrop) {
+        applyJsonDropPayload(assetPayload, (p) => p.path, onAssetDrop, placement);
         return;
       }
       const blockPayload = e.dataTransfer.getData(TIMELINE_BLOCK_MIME);
-      if (blockPayload && onBlockDrop && scroll && rect) {
-        try {
-          const parsed = JSON.parse(blockPayload) as { name?: string };
-          if (parsed.name)
-            void onBlockDrop(
-              parsed.name,
-              resolveTimelineAssetDrop(dropInput, e.clientX, e.clientY),
-            );
-        } catch {
-          /* ignore malformed drag payloads */
-        }
+      if (blockPayload && onBlockDrop) {
+        applyJsonDropPayload(blockPayload, (p) => p.name, onBlockDrop, placement);
       }
     },
-    [
-      onAssetDrop,
-      onBlockDrop,
-      onFileDrop,
-      scrollRef,
-      ppsRef,
-      durationRef,
-      trackOrderRef,
-      timelineLayersRef,
-    ],
+    [resolveDropPlacement, onFileDrop, onAssetDrop, onBlockDrop],
   );
 
-  return { isDragOver, setIsDragOver, handleAssetDragOver, handleAssetDrop };
+  return { isDragOver, handleAssetDragOver, handleAssetDrop, clearDropPreview };
 }