#20533: fix: strip resolvedSkills from session store to prevent snapshot bloat

## Problem Fixes #20528 `buildWorkspaceSkillSnapshot()` stores full `Skill` objects (name, description, filePath, etc.) in `resolvedSkills`, which gets serialized to `sessions.json`. With 3,138 built-in skills this adds ~2.9 MB per session entry, causing `sessions.json` to grow to hundreds of MB/day with frequent cron jobs. ## Solution 1. **`normalizeSessionStore()`** now strips `resolvedSkills` from each session's `skillsSnapshot` before persisting to disk. The lightweight `skills` array (`name` + `primaryEnv`) remains — sufficient for cache-hit checks. 2. **`shouldLoadSkillEntries`** in both `attempt.ts` and `compact.ts` now checks `skills.length > 0` as a fallback when `resolvedSkills` is absent (i.e. session restored from disk), so skill env overrides still work correctly without re-scanning the filesystem. ## Impact - Session snapshots go from ~2.9 MB → ~18 KB per entry - No behavioral change for in-memory runtime (resolvedSkills still populated during the session) - Existing bloated sessions.json files are cleaned up on next write <!-- greptile_comment --> <h3>Greptile Summary</h3> Strips the heavy `resolvedSkills` field (full Skill objects with name, description, filePath) from session snapshots before persisting to disk, reducing session storage from ~2.9 MB to ~18 KB per entry. The lightweight `skills` array (name + primaryEnv) remains sufficient for cache-hit checks and environment overrides. **Key changes:** - `normalizeSessionStore()` now removes `resolvedSkills` before disk persistence - Updated fallback logic in `attempt.ts` and `compact.ts` to check `skills.length > 0` when `resolvedSkills` is absent - No behavioral changes for runtime (resolvedSkills still populated during active sessions) - Existing bloated sessions.json files automatically cleaned on next write <h3>Confidence Score: 5/5</h3> - This PR is safe to merge with minimal risk - The changes are surgical, well-scoped, and address a clear performance issue. The logic correctly preserves the lightweight `skills` array for cache checks and env overrides while removing only the redundant heavy `resolvedSkills` field. The fallback condition properly handles all three scenarios: fresh sessions, in-memory sessions with resolvedSkills, and restored sessions with only the lightweight skills array. - No files require special attention _{Last reviewed commit: dba2024} <!-- greptile_other_comments_section --> <!-- /greptile_comment -->