feat(routing): add DISABLE_CONTEXT_WINDOW_CHECKS bypass for the direct-request input/context check (#10927)

Rescoped from #10606 — see PR body for the full rationale (combo-routing half made moot by #10162's advisory-only architecture, chatCore.ts hard-reject bypass retains real value).

Validated in an isolated worktree boarded onto origin/release/v3.8.50:
- 65/65 focused unit tests pass (chatcore-model-output-cap-wiring + feature-flags-settings).
- check-file-size, check-changelog-integrity: OK.
- typecheck:core: clean.
- check-complexity / check-cognitive-complexity: OK, both under baseline.

Co-authored-by: JxnLexn <10897478+JxnLexn@users.noreply.github.com>

src/shared/constants/featureFlagDefinitions.ts

@@ -236,7 +236,7 @@ export const FEATURE_FLAG_DEFINITIONS: FeatureFlagDefinition[] = [
     warningLevel: "info",
   },
 
-  // ──────────────── Policies (4) ────────────────
+  // ──────────────── Policies (5) ────────────────
   {
     key: "TOOL_POLICY_MODE",
     label: "Tool Policy Mode",
@@ -271,6 +271,18 @@ export const FEATURE_FLAG_DEFINITIONS: FeatureFlagDefinition[] = [
     requiresRestart: true,
     warningLevel: "info",
   },
+  {
+    key: "DISABLE_CONTEXT_WINDOW_CHECKS",
+    label: "Disable Context Window Checks",
+    description:
+      "Skip OmniRoute's local context-window and max-input-token check for direct single-model requests. Upstream providers remain responsible for enforcing their actual limits. Off by default.",
+    descriptionI18nKey: "featureFlagDisableContextWindowChecksDescription",
+    category: "policies",
+    defaultValue: "false",
+    type: "boolean",
+    requiresRestart: false,
+    warningLevel: "danger",
+  },
   {
     key: "CAPABILITY_FILTER_ENABLED",
     label: "Capability Filter",

src/shared/utils/featureFlags.ts

@@ -72,6 +72,22 @@ export function isCcCompatibleProviderEnabled(): boolean {
   return isFeatureFlagEnabled("ENABLE_CC_COMPATIBLE_PROVIDER");
 }
 
+/**
+ * Context-window checks are fail-safe: an unavailable flag store must never
+ * silently disable local request bounds.
+ */
+export function areContextWindowChecksDisabled(): boolean {
+  try {
+    return isFeatureFlagEnabled("DISABLE_CONTEXT_WINDOW_CHECKS");
+  } catch (error) {
+    console.error(
+      "[featureFlags] Failed to resolve DISABLE_CONTEXT_WINDOW_CHECKS, keeping checks enabled:",
+      error instanceof Error ? error.message : error
+    );
+    return false;
+  }
+}
+
 export function isApiKeyRevealEnabledFlag(): boolean {
   try {
     return isFeatureFlagEnabled("ALLOW_API_KEY_REVEAL");