fix: Suppress VGitSync during staging; 95%+ performance improvement

[MaxFangX]

Builds on top of #422 and #423.

Description

Fixes performance degradation during staging operations by suppressing redundant VGitSync broadcasts. Achieves 99.6% reduction in buffer refresh calls (1,380 -> 6 LiveGutter:fetch calls) and 95% reduction in total git operations (10,421 -> 564 calls across 41 staging operations).

When staging hunks, every git index change triggered a cascade: filesystem watcher detects change -> VGitSync event fires -> git_buffer_store.for_each() iterates all tracked buffers -> each buffer runs LiveGutter:fetch() -> GitBuffer:diff() -> 3-4 git commands per buffer. With 15 tracked buffers, this meant 15x unnecessary buffer refreshes per stage operation, resulting in thousands of redundant git command calls.

This adds suppress_sync_and_refresh(buffer, ms) API to git_buffer_store that temporarily suppresses VGitSync broadcasts and refreshes only the specified buffer after a delay. Applied to all DiffScreen staging methods (stage_hunk, unstage_hunk, reset_hunk, stage, unstage, reset) and Hunks buffer operations (stage_all, cursor_stage).

Note: External git operations during the suppression window (~200ms) won't trigger a refresh until the next VGitSync event — an acceptable tradeoff given the short window.

Tested with 15 tracked buffers over 41 staging operations. No functional regressions observed - all git operations complete successfully, gutter signs update correctly, and UI remains responsive.

Performance Summary

Improvement:

• Total calls: 95% reduction (10,421 -> 564)
• LiveGutter:fetch: 99.6% reduction (1,380 -> 6)
• GitBuffer:diff: 99.6% reduction (1,381 -> 6)
• git ls-files: 94% reduction (1,463 -> 87)

Profiling Details

Environment: 15 tracked buffers, ~40 stage operations (DiffScreen:stage_hunk)

Before:

Unique operations: 36
Total calls: 10,421

156054ms total (1380x, 113ms avg) - vgit.features.buffer.LiveGutter:fetch
102827ms total (1381x, 74ms avg) - vgit.git.GitBuffer:diff
69420ms total (1838x, 38ms avg) - vgit.git.git_buffer_store.dispatch
41300ms total (1463x, 28ms avg) - gitcli.run: git ls-files
20863ms total (768x, 27ms avg) - gitcli.run: git ls-files -u
18357ms total (468x, 39ms avg) - gitcli.run: git show
11166ms total (39x, 286ms avg) - vgit.features.screens.DiffScreen:stage_hunk

After:

Unique operations: 21
Total calls: 564

6502ms total (41x, 159ms avg) - vgit.features.screens.DiffScreen:stage_hunk
1410ms total (87x, 16ms avg) - gitcli.run: git ls-files
723ms total (38x, 19ms avg) - vgit.git.git_stager.stage_hunk
339ms total (6x, 57ms avg) - vgit.git.git_buffer_store.dispatch
242ms total (6x, 40ms avg) - vgit.features.buffer.LiveGutter:fetch
241ms total (6x, 40ms avg) - vgit.git.GitBuffer:diff

[luisdavim]

This seems like a great improvement, any reason not to merge it?

[MaxFangX]

This seems like a great improvement, any reason not to merge it?

I think it was because there were merge conflicts after #422 and #423 were merged (which this PR built on top of).

Rebased.

[MaxFangX]

Pushed a change which does the same thing with a different approach: suppress_sync_and_refresh. Instead of having to remember to manually refresh that buffer, we require it in the params and handle the buffer refresh after a timeout. The VGitSync suppression behavior is still intact, preventing our staging operations from triggering a refresh of all buffers. I also applied the suppression to Hunks buffer operations outside of DiffScreen.