[jjxyxsjr]

Problem and behavior

Large request bodies can legitimately sit silent well past the flat 30s direct response-start window: prefill scales with input size, and a plain large-context request carries no reasoning_effort selector for the existing reasoning ceiling (REASONING_READINESS_CEILING_MS) to key on — so the fetch-layer guard cut healthy slow-prefill upstreams at exactly the floor and surfaced 504s the stream-readiness layer would have permitted.

Changes

• resolveFlatDirectHeadersFloorMs raises the flat floor by payload tier: ≤512 KB unchanged (a small body overrunning the probe still smells like a dead connection, per fix(network): direct dispatcher stalls opencode-go and command-code until service restart #10214), >512 KB ×2, >2 MB ×3, capped at 180 s — composing with the existing effort/local raises via raise-only semantics.
• New env OMNIROUTE_DIRECT_HEADERS_VOLUME_ADAPTIVE (0/false/off pins the flat behavior), registered in .env.example and docs/reference/ENVIRONMENT.md.

Validation

TDD — tests/unit/direct-response-start-timeout-volume-tier.test.ts failed before the fix on 4/7 (the resolver returned the flat 30000 for every tier), passes 7/7 after:

not ok 2 - 2. >512KB doubles the floor                       (expected 60000, got 30000)
not ok 3 - 3. >2MB triples the floor                         (expected 90000, got 30000)
not ok 4 - 4. tier raise is capped at the 180s volume ceiling (expected 180000, got 30000)
not ok 7 - 7. resolver binds the body once per request        (expected 60000, got 30000)

• Regressions: direct-response-start-timeout-reasoning-504.test.ts + direct-response-start-timeout-settled-guard-12861.test.ts — 17 pass.
• npm run check:env-doc-sync in sync · eslint clean on the touched module.
• Only the files the failing test proves need changing are touched; no test weakened or deleted.

Notes

• Raise-only composition: the volume tier applies last as max(base, min(base * factor, 180s)), composes order-independently with the effort and local/LAN raises, and can never pull the window below an operator override or the local floor (test 4 pins the cap, test 5 pins the never-lower rule).
• Byte length uses TextEncoder on the already-serialized body string the resolver binds once per request (same binding the reasoning-effort regex uses) — no extra serialization on the request path.
• Default (OMNIROUTE_DIRECT_HEADERS_VOLUME_ADAPTIVE unset) = enabled tiering as described; the kill switch restores today's flat behavior exactly.
• Base: release/v3.8.53 (active release branch); aware of the 3.8.55 v4-feature retarget policy.