[matchai]

A walkthrough-file launch reads the repository diff twice: once for the launch check (#187) and again when the window loads the walkthrough. The window's first walkthrough load now reuses the state the check already read, so the diff is read once.

 openLaunchWindow
   read repository state
   check walkthrough file
   focusOrCreateWindow(…, state)
+  windowWalkthroughFileStates.set(window, state)
 codiff:getNarrativeWalkthrough
-  readRepositoryStateWithConfig()
+  use the launch's state on the window's first walkthrough load

The state is dropped after one use and when the window closes, so later loads, including forced reloads, read the diff as before. The first load needs no force or source check: the renderer never forces it and always asks for the source the window opened with. createWindow now returns its window so the launch can record it.

Timings

5 cold launches of codiff -w --walkthrough-file <valid file> per version, alternating between main (da35d91) and this PR (442e51f) so both ran under the same load. The later simplification (c899c9b) only removes guards that never fired, so the read pattern is unchanged. Times are medians from the command's start, traced in Electron's main process on dev builds.

Milestone	main	This PR
Repository reads	2	1
CLI exits (launch check done)	500 ms	550 ms
Window visible	838 ms	824 ms
Walkthrough IPC, request to response	429 ms	1 ms
Walkthrough loaded	1,154 ms	755 ms

The walkthrough now loads about 0.4 s sooner, about 35% faster. The rest of startup is unchanged within run-to-run noise. The first main run was a 5.7 s cold-cache outlier, which the median absorbs.

Merge danger: two-way door, walkthrough-file launches only. The first walkthrough load trusts that it asks for the launch's source; a future caller that first loads a different source would get the launch's diff.

This PR was written primarily with fx, a coding agent. I reviewed the change; the agent traced the launch, wrote the change, and measured it against main.

banana banana banana

[cpojer]

Your other PR fixed this, too.