#10997: fix: enable cache-ttl pruning on first load after restart

## Summary Fixes context overflow on first request after gateway restart when cache-ttl pruning is enabled. ## Problem When `lastCacheTouchAt` was null (on first load after restart), the cache-ttl pruning logic would skip pruning entirely. This caused sessions with large histories to immediately overflow before pruning could occur. ## Solution Modified the TTL check to only skip pruning when: - `lastCacheTouchAt` is NOT null AND - TTL hasn't expired Now pruning runs on first load (when `lastCacheTouchAt` is null) and after TTL expires, then sets `lastCacheTouchAt` for future TTL checks. ## Changes - **File**: `src/agents/pi-extensions/context-pruning/extension.ts` - Changed condition from `if (!lastTouch || ttlMs <= 0)` to `if (lastTouch !== null && ttlMs > 0 && Date.now() - lastTouch < ttlMs)` - Added explanatory comments - **Tests**: `src/agents/pi-extensions/context-pruning.test.ts` - Added new test: `cache-ttl prunes on first load when lastCacheTouchAt is null` - Verifies pruning happens on first load - Verifies `lastCacheTouchAt` is set after first prune ## Testing ✅ All existing tests pass ✅ New test validates first-load pruning behavior ✅ Full `pnpm check` passes (lint, format, typecheck) Fixes #10986 <!-- greptile_comment --> <h2>Greptile Overview</h2> <h3>Greptile Summary</h3> - Adjusts `cache-ttl` context-pruning gating so pruning runs on first request after restart (when `lastCacheTouchAt` is `null`) and continues to be skipped only while the TTL window is still active. - Keeps existing pruning flow unchanged: `pruneContextMessages(...)` runs and, if it produced changes, updates `runtime.lastCacheTouchAt` to start/reset the TTL window. - Adds a regression test covering the “first load with null lastCacheTouchAt” case and asserts that `lastCacheTouchAt` is set after the first prune. <h3>Confidence Score: 5/5</h3> - This PR looks safe to merge and addresses the reported first-load pruning skip without changing pruning behavior outside cache-ttl gating. - Change is narrowly scoped to the cache-ttl early-return condition, maintains existing behavior for ttlMs<=0 and within-TTL requests, and includes a targeted regression test that exercises the previously failing scenario (null lastCacheTouchAt) plus existing ttl-window tests. - No files require special attention <!-- greptile_other_comments_section --> _{(2/5) Greptile learns from your feedback when you react with thumbs up/down!} <!-- /greptile_comment -->