Make repo-memory max-patch-size pre-check measure the push diff, not the whole folder

[nestele]

Summary

repo-memory's max-patch-size is documented as a per-push diff limit, but the MCP pre-check measures the whole memory folder instead. This blocks pushes even when the actual change is tiny. #42773 was closed by #43301, which only reworded the error message — the behavior is unchanged.

Current behavior

Two checks share the same max-patch-size:

• actions/setup/js/push_repo_memory.cjs — measures the git diff. ✅ matches docs.
• actions/setup/js/safe_outputs_handlers.cjs — sums the byte size of every file in the folder. ❌ undocumented, contradicts docs.

The docs only define per-file (max-file-size), file-count (max-file-count), and per-push diff (max-patch-size). No total-folder limit exists anywhere in the docs.

Impact

Once accumulated files exceed the limit, every push is rejected — even a one-line change — with no way to satisfy it.

Fix

Make the pre-check use the same diff-based logic as the push gate. Do not add a total-folder limit.

Implementation plan

1. In safe_outputs_handlers.cjs, replace the total-file-size sum with the staged git diff size (same calculation as push_repo_memory.cjs).
2. Extract that diff-size calculation into one shared helper so both checks call the same function.
3. Add tests: a tiny diff on a large folder passes; an oversized diff fails.

References

• Docs: https://github.github.com/gh-aw/reference/repo-memory/
• push_repo_memory: pre-check measures total content, push gate measures diff additions — same config knob, mismatched semantics + misleading error #42773, fix(push_repo_memory): correct misleading "git diff format overhead" framing in pre-check error message #43301