## What
Extends `editHistory.test.ts` with T11 from the SDK migration test plan: history coalescing gaps and origin guard stubs.
## Tests
**New passing test (1):**
- **cross-prop coalescing separation** — two edits within the coalesce window but with *different* `coalesceKey` values produce two separate undo entries, not one coalesced entry. Fills the gap left by the existing same-file coalescing tests (lines 176–243).
**`.todo` stubs (2):**
- `gesture-start/commit collapses intermediate drag steps into one undo entry` — requires gesture lifecycle API not yet built
- `origin:applyPatches edits excluded from undo stack` — requires SDK session object (`session.on("patch", ...)`, `session.dispatch(...)`) which doesn't exist yet; needed to prevent undo loops when SDK patches are applied
## Stack
Stacked on T8 (#1241). Prerequisite for T4 (#1243).
Vance Ingalls
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