#22901: fix: guard against NaN reserveTokens in compaction safeguard

## Summary - Adds `|| 0` fallback for `preparation.settings.reserveTokens` in both occurrences within `compaction-safeguard.ts` - When `reserveTokens` is undefined, `Math.floor(undefined)` returns `NaN`, and `Math.max(1, NaN)` also returns `NaN`, causing summarization to fail silently - With the fallback, `Math.max(1, Math.floor(0))` correctly resolves to `1` Fixes #9279 ## Local Validation - [x] Both occurrences of `preparation.settings.reserveTokens` are guarded (lines 278 and 300) - [x] `|| 0` correctly handles `undefined`, `null`, `NaN`, and `0` inputs ## Scope XS — 2-line change in one file ## AI Assistance Used Claude Code for issue investigation and fix implementation. ## Author @miloudbelarebia 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com> <!-- greptile_comment --> <h3>Greptile Summary</h3> Minimal 2-line defensive fix in `compaction-safeguard.ts` that guards against `NaN` propagation when `preparation.settings.reserveTokens` is `undefined`. Without the fix, `Math.floor(undefined)` produces `NaN`, and `Math.max(1, NaN)` also returns `NaN`, which would be passed to `summarizeInStages` causing summarization to fail silently. The `|| 0` fallback ensures `Math.max(1, Math.floor(0))` correctly resolves to `1` — a safe minimum. - Both occurrences of `preparation.settings.reserveTokens` (lines 278 and 300) are now consistently guarded - The fix correctly handles `undefined`, `null`, `NaN`, and `0` inputs - No issues found during review <h3>Confidence Score: 5/5</h3> - This PR is safe to merge — it's a minimal defensive fix with no behavioral change when reserveTokens is already a valid number. - The change is a 2-line fix in a single file, adding a standard JS falsy fallback. The logic is straightforward: `|| 0` guards against `undefined`/`NaN`, and the outer `Math.max(1, ...)` ensures a minimum of 1. Both occurrences are handled consistently. No new code paths, no API changes, no risk of regression. - No files require special attention. _{Last reviewed commit: 11e1133} <!-- greptile_other_comments_section --> <!-- /greptile_comment -->