fix(search): check the last shortened read window against its budget - #9987

Summary

• encodedWindowEnd shortened a window up to three times but returned before checking the third shortened window, so a window that fit its budget fell back to the 8K minimum
• It now checks every window it computes and computes none it doesn't check. Text whose escaped characters come first (quotes, backslashes, line breaks) gets the longer window it fits instead of the standard page

Type of Change

• Bug fix

Testing

• New read-window.test.ts case fails on the previous loop (8000 instead of 19000) and passes now
• bun run test lib/sim-search/live lib/knowledge/mcp (513 passed), biome on changed files

Checklist

• Code follows project style guidelines
• Self-reviewed my changes
• Tests added/updated and passing (new tests pass the test-audit authoring gate)
• No new warnings introduced
• I confirm that I have read and agree to the terms outlined in the Contributor License Agreement (CLA)