What Problem This Solves

Source builds of current main fail deterministically on machines whose zlib packs slightly worse than CI's: pnpm build reports "startup JS gzip: 312.1 KiB exceeds 312.0 KiB" (reproduced twice on the team.openclaw.ai deployment host after #111909 landed). Main sat within ~0.1 KiB of the ceiling, so the budget passes or fails on compression variance rather than on an intentional loading decision.

Why This Change Was Made

The startup catalog grew by the widget sandbox-origin diagnostic strings (#111909), consuming the last of the previous ratchet's headroom. Per the file's own convention, budget changes accompany an intentional decision: 313 KiB restores explicit headroom for that feature and is documented in place, following the same pattern as the prior live-narration bump.

User Impact

pnpm build succeeds again on source checkouts regardless of local zlib packing; no runtime behavior changes.

Evidence

• Two consecutive clean-cache pnpm build runs on the deployment host at bf6961d failed with the identical 312.1 vs 312.0 violation; CI's build lane passed the same commits, demonstrating environment-dependent gzip variance at the cliff.
• Diff is the budget constant plus its justification comment only (5+/4-).
• Autoreview (codex gpt-5.6-sol, xhigh): clean, "patch is correct (0.98)". A first iteration also shortened the diagnostic string; review flagged the lost routing guidance, so the string is untouched and only the budget moves.