fix(sse): make MAX_TOOLS_LIMIT configurable via env var

[70nyIT]

⚠️ base-red inherited: #15100

Summary

• MAX_TOOLS_LIMIT now reads OMNIROUTE_MAX_TOOLS_LIMIT through the existing envInt() helper: default 128, positive integers only. Unset or invalid values keep the current 128 behavior, so nothing changes by default.
• truncateToolList() now evaluates bypassDefaultToolLimit before the known/detected provider limit. The getKnownToolLimit() branch used to return first, so once a provider limit was cached or detected the operator override was silently ignored.
• The new var is documented in .env.example (§6 Tool & Routing Policies) and docs/reference/ENVIRONMENT.md (§6), matching the other envInt() knobs already listed there.
• Request tool lists are still clipped to the same caps as before when no override and no bypass is requested.

Related Issues

• Fixes feat(backend): Make tool-list cap (MAX_TOOLS_LIMIT=128) configurable via env var #13190

Validation

• Change type: routing
• Focused tests and category gates from the golden path
• npm run lint (pre-commit lint-staged on the changed files)
• Reconciled with the current active release base; focused checks rerun afterward
• Production-code changes include a new or updated automated test in this PR

Commands run:

• node --import tsx/esm --test tests/unit/chatcore-upstream-body.test.ts tests/unit/max-tools-limit-env.test.ts → 45 pass / 0 fail
• node --import tsx/esm --test tests/unit/cache-sweeps.test.ts → 26 pass / 0 fail
• npm run typecheck:core → clean
• npx eslint <changed files> → clean
• npm run check:env-doc-sync → clean (864 vars in .env.example, 881 in ENVIRONMENT.md, all in sync)
• npm run check:docs-sync and npm run check:fabricated-docs → clean
• npm run check:docs-counts → fails only on the inherited base drift (README.md / llm.txt still say 3.8.51), which is 🔴 Release branch not green: release/v3.8.52 #15100 and is untouched by this branch.

TDD proof for the bypass fix: temporarily restoring the old ordering makes the new regression test fail with expected: 250, actual: 200; with the reorder it passes.

Tests Added Or Updated

• tests/unit/chatcore-upstream-body.test.ts — regression: "operator bypass wins over a known provider limit"
• tests/unit/max-tools-limit-env.test.ts (new) — unset ⇒ 128, OMNIROUTE_MAX_TOOLS_LIMIT=512 ⇒ 512, non-positive-integer values ⇒ 128

Coverage Notes

• open-sse/config/constants.ts: the load-time parse is exercised by the new env override test.
• open-sse/handlers/chatCore/upstreamBody.ts: the truncation/bypass path is exercised by tests/unit/chatcore-upstream-body.test.ts.

Reviewer Notes

• Documentation updated: OMNIROUTE_MAX_TOOLS_LIMIT (default 128, positive integers only, invalid values fall back to 128) is listed in .env.example §6 and docs/reference/ENVIRONMENT.md §6. It only moves the default ceiling — a provider with a known/proactive limit (grok-cli 200, nvidia 1536) still applies its own cap.
• Base release/v3.8.52 is currently red (🔴 Release branch not green: release/v3.8.52 #15100); any failures inherited from the base are not caused by this branch.