## Summary
Harden the `ChangeTracker` lifecycle to eliminate the class of bugs
where an inactive workflow's tracker silently captures the wrong graph
state. Renames `checkState()` to `captureCanvasState()` with a
self-defending assertion, introduces `deactivate()` and
`prepareForSave()` lifecycle methods, and closes a latent undo-history
corruption bug discovered during code review.
## Background
ComfyUI supports multiple workflows open as tabs, but only one canvas
(`app.rootGraph`) exists at a time. When the user switches tabs, the old
workflow's graph is unloaded and the new one is loaded into this shared
canvas.
The old `checkState()` method serialized `app.rootGraph` into
`activeState` to track changes for undo/redo. It had no awareness of
*which* workflow it belonged to -- if called on an inactive tab's
tracker, it would capture the active tab's graph data and silently
overwrite the inactive workflow's state. This caused permanent data loss
(fixed in PR #10745 with caller-side `isActive` guards).
The caller-side guards were fragile: every new call site had to remember
to add the guard, and forgetting would reintroduce the same silent data
corruption. Additionally, `beforeLoadNewGraph` only called `store()`
(viewport/outputs) without `checkState()`, meaning canvas state could be
stale if a tab switch happened without a preceding mouseup event.
### Before (fragile)
```
saveWorkflow(workflow):
if (isActive(workflow)) <-- caller must remember this guard
workflow.changeTracker.checkState() <-- name implies "read", actually writes
...
beforeLoadNewGraph():
activeWorkflow.changeTracker.store() <-- only saves viewport, NOT graph state
```
### After (self-defending)
```
saveWorkflow(workflow):
workflow.changeTracker.prepareForSave() <-- handles active/inactive internally
...
beforeLoadNewGraph():
activeWorkflow.changeTracker.deactivate() <-- captures graph + viewport together
```
## Changes
- Rename `checkState` to `captureCanvasState` with active-tracker
assertion
- Add `deactivate()` and `prepareForSave()` lifecycle methods
- Fix undo-history corruption: `captureCanvasState()` guarded by
`_restoringState`
- Fix viewport regression during undo: `deactivate()` skips
`captureCanvasState()` during undo/redo but always calls `store()` to
preserve viewport (regression from PR #10247)
- Log inactive tracker warnings unconditionally at warn level (not
DEV-only)
- Deprecated `checkState()` wrapper for extension compatibility
- Rename `checkState` to `captureCanvasState` in
`useWidgetSelectActions` composable
- Add `appModeStore.ts` to manual call sites documentation
- Add `checkState()` deprecation note to architecture docs
- Add 16 unit tests covering all guard conditions, lifecycle methods,
and undo behavior
- Add E2E test: "Undo preserves viewport offset"
## New ChangeTracker Public API
| Method | Caller | Purpose |
|--------|--------|---------|
| `captureCanvasState()` | Event handlers, UI interactions | Snapshots
canvas into activeState, pushes undo. Asserts active tracker. |
| `deactivate()` | `beforeLoadNewGraph` only | `captureCanvasState()`
(skipped during undo/redo) + `store()`. Freezes state for tab switch. |
| `prepareForSave()` | Save paths only | Active: `captureCanvasState()`.
Inactive: no-op. |
| `checkState()` | **Deprecated** -- extensions only | Wrapper that
delegates to `captureCanvasState()` with deprecation warning. |
| `store()` | Internal to `deactivate()` | Saves viewport, outputs,
subgraph navigation. |
| `restore()` | `afterLoadNewGraph` | Restores viewport, outputs,
subgraph navigation. |
| `reset()` | `afterLoadNewGraph`, save | Resets initial state (marks as
"clean"). |
## Test plan
- [x] Unit tests: 16 tests covering all guard conditions, state capture,
undo queue behavior
- [x] E2E test: "Undo preserves viewport offset" verifies no viewport
drift on undo
- [x] E2E test: "Prevents captureCanvasState from corrupting workflow
state during tab switch"
- [x] Existing E2E: "Closing an inactive tab with save preserves its own
content"
- [ ] Manual: rapidly switch tabs during undo/redo, verify no viewport
drift
- [ ] Manual: verify extensions calling `checkState()` see deprecation
warning in console
