fix(translator): strip multipleOf from antigravity/gemini tool schemas (port from 9router#2309) (#6052)

`multipleOf` is not part of the Gemini/antigravity OpenAPI 3.0 schema subset, so
leaving it in function_declaration parameters triggered a hard upstream 400
("Unknown name multipleOf"). Add it to GEMINI_UNSUPPORTED_SCHEMA_KEYS so it is
stripped at every schema level; minimum/maximum stay (Gemini accepts them).

Reported-by: abil0321 (https://github.com/decolua/9router/issues/2309)

CHANGELOG.md

@@ -26,6 +26,8 @@
 
 - **kiro (system prompt leaked as raw user text):** when Claude Code routed through the Kiro/CodeWhisperer backend, the `system` message was normalized to a `user` turn with no wrapper, so the entire system prompt (environment info, tool definitions, memory instructions, etc.) appeared as if the user had typed it — polluting the model context. System-origin content is now wrapped in `<system-reminder>` tags before being merged into the Kiro user message, so the model can distinguish it from real user input. Real user turns are untouched. Regression guard: `tests/unit/kiro-system-reminder-2306.test.ts`. (thanks @VitzS7)
 
+- **antigravity/gemini tool calls (`400 Unknown name "multipleOf"`):** requests routed to antigravity/gemini models with tools that declare a `multipleOf` numeric constraint failed with a hard upstream `400` (`Invalid JSON payload received. Unknown name "multipleOf"`). `multipleOf` is not part of the Gemini/antigravity OpenAPI 3.0 schema subset and was not being stripped from `function_declarations`. It is now removed at every schema level (top-level, nested, and array `items`), alongside the other unsupported constraints; `minimum`/`maximum` remain untouched. Regression guard: `tests/unit/gemini-multipleof-2309.test.ts`. (thanks @abil0321)
+
 ### 📝 Maintenance
 
 - **test (deflake `setup-claude`):** `tests/unit/cli/setup-claude.test.ts` failed ~50% of runs with `Unable to deserialize cloned data due to invalid or unsupported version` at file teardown (all subtests passed), randomly reddening `Unit Tests fast-path (2/2)` / `Fast Quality Gates` across the PR→release queue. Root cause: `node --test` streams each file's report to the parent as V8-serialized frames on fd 1 (stdout), and the CLI helper under test (`syncClaudeProfilesFromModels`) prints progress via `console.log` — that stdout output interleaved with the serialized frames and corrupted the stream. The test now silences the stdout-writing `console` methods for the file's duration (no assertion inspects stdout), making it deterministic (15/15 green locally). ([#5959](https://github.com/diegosouzapw/OmniRoute/issues/5959))

open-sse/translator/helpers/geminiHelper.ts

@@ -12,6 +12,10 @@ export const GEMINI_UNSUPPORTED_SCHEMA_KEYS = new Set([
   "maxLength",
   "exclusiveMinimum",
   "exclusiveMaximum",
+  // `multipleOf` is not part of the Gemini/antigravity OpenAPI 3.0 schema subset;
+  // leaving it in function_declarations triggers a hard upstream 400
+  // ("Unknown name \"multipleOf\""). `minimum`/`maximum` ARE accepted and kept.
+  "multipleOf",
   // NOTE: `pattern` is intentionally NOT in this set. Antigravity (Gemini-derived
   // surface) accepts `pattern` on string constraints, and glob/grep/file-search
   // tools depend on it to express their argument regex. Removing it produced

tests/unit/gemini-multipleof-2309.test.ts

@@ -0,0 +1,41 @@
+/**
+ * #2309 — antigravity/gemini returned [400] "Invalid JSON payload received.
+ * Unknown name \"multipleOf\" at 'request.tools[0].function_declarations[...]"
+ *
+ * Root cause: `multipleOf` (a JSON Schema numeric constraint) was NOT listed in
+ * `GEMINI_UNSUPPORTED_SCHEMA_KEYS`, so `cleanJSONSchemaForAntigravity` left it in
+ * the function-declaration parameters. The Gemini/antigravity upstream (OpenAPI
+ * 3.0 schema subset) rejects `multipleOf` with a hard 400.
+ *
+ * Fix: add `multipleOf` to the unsupported-keys set so it is stripped at every
+ * level (top-level property, nested object, and inside array `items`). Sibling
+ * numeric constraints `minimum`/`maximum` ARE accepted by Gemini and must stay.
+ */
+import test from "node:test";
+import assert from "node:assert/strict";
+
+import {
+  cleanJSONSchemaForAntigravity,
+  GEMINI_UNSUPPORTED_SCHEMA_KEYS,
+} from "../../open-sse/translator/helpers/geminiHelper.ts";
+
+test("#2309 multipleOf is stripped at all levels for antigravity/gemini schemas", () => {
+  const schema = {
+    type: "object",
+    properties: {
+      count: { type: "integer", multipleOf: 2, minimum: 0 },
+      ratio: { type: "number", multipleOf: 0.5 },
+      tags: { type: "array", items: { type: "number", multipleOf: 10 } },
+    },
+  };
+
+  const cleaned = JSON.stringify(cleanJSONSchemaForAntigravity(schema));
+
+  assert.ok(!cleaned.includes("multipleOf"), "multipleOf must be removed");
+  // Gemini DOES support minimum/maximum — those must survive.
+  assert.ok(cleaned.includes("minimum"), "minimum must be preserved");
+});
+
+test("#2309 multipleOf is in GEMINI_UNSUPPORTED_SCHEMA_KEYS", () => {
+  assert.ok(GEMINI_UNSUPPORTED_SCHEMA_KEYS.has("multipleOf"));
+});