git-sync-bench: exit non-zero on failed runs, drop -1 sentinels

[Soph]

Problems

Two reporting bugs in cmd/git-sync-bench:

1. Always exited 0. run() returned nil after printing the report regardless of outcome, so the process exited 0 even when every benchmark run failed — a failure silently passed for success in CI.
2. -1 sentinels in output. The aggregate Min* fields start at -1 as an "unset" marker updated by the first qualifying run. With no successful (or no batched) run, the sentinel survived into the report — emitting "minWallMillis": -1, "minSyncElapsedMillis": -1, etc.

Fix

• Print the report (JSON or text) as before, then return an error when Aggregate.FailedRuns > 0, so main exits non-zero. The report stays the useful artifact; the exit code now reflects reality.
• Clear the Min* sentinels to 0 when there were no qualifying runs (the batch-count fields are omitempty, so 0 drops them entirely).

Tests

TestSummarizeRunsAllFailedHasNoSentinels runs an all-failed set and asserts the counts, that the Min* fields are 0, and that the marshaled JSON contains no -1. The existing TestSummarizeRuns (mixed success) still passes.

🤖 Generated with Claude Code

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Note

Low Risk
Benchmark CLI reporting and exit behavior only; no sync/runtime logic changes.

Overview
git-sync-bench now prints the full report (JSON or text) and then returns an error when any benchmark run failed, so main exits 1 instead of always succeeding in CI.

summarizeRuns resets aggregate Min* fields from the internal -1 “unset” sentinel to 0 when there are no successful runs (wall/sync mins) or no batched runs (batch mins), so JSON/text reports no longer show minWallMillis: -1 and similar.

Adds TestSummarizeRunsAllFailedHasNoSentinels to lock in all-failed aggregation and JSON without -1.

^{Reviewed by Cursor Bugbot for commit db22241. Configure here.}