fix(llm): default Gemini supportsParallelTools to false

src/config/config-schema.ts

@@ -769,6 +769,7 @@ export interface AtomicAgentConfig {
       apiKeyHeader?: string;
       supportsTools?: boolean;
       supportsVision?: boolean;
+      supportsParallelTools?: boolean;
       requestTimeoutMs?: number;
       promptCache?: "auto" | "off" | "explicit-markers";
       providerPreferences?: Record<string, unknown>;

src/config/llm-config.test.ts

@@ -505,4 +505,82 @@ describe("llm-config", () => {
       }),
     ).toThrow(/extraArgs\[1\]/);
   });
+
+  it("round-trips supportsParallelTools through parseLlmProviderEntry", () => {
+    const parsed = parseUserConfigFile({
+      version: USER_CONFIG_VERSION,
+      llm: {
+        activeTextProvider: "gemini",
+        activeEmbeddingProvider: "gemini",
+        toolTransport: "auto",
+        providers: [
+          {
+            id: "gemini",
+            kind: "gemini",
+            baseUrl: "https://generativelanguage.googleapis.com",
+            apiKey: "test-key",
+            defaultChatModel: "gemini-2.5-flash",
+            supportsParallelTools: false,
+          },
+          {
+            id: "openai",
+            kind: "openai-compatible",
+            baseUrl: "https://api.openai.com",
+            apiKey: "test-key",
+            defaultChatModel: "gpt-4o",
+            supportsParallelTools: true,
+          },
+        ],
+      },
+    });
+    const gemini = parsed.llm?.providers.find((p) => p.id === "gemini");
+    expect(gemini?.supportsParallelTools).toBe(false);
+    const openai = parsed.llm?.providers.find((p) => p.id === "openai");
+    expect(openai?.supportsParallelTools).toBe(true);
+  });
+
+  it("accepts undefined supportsParallelTools (absent field)", () => {
+    const parsed = parseUserConfigFile({
+      version: USER_CONFIG_VERSION,
+      llm: {
+        activeTextProvider: "gemini",
+        activeEmbeddingProvider: "gemini",
+        toolTransport: "auto",
+        providers: [
+          {
+            id: "gemini",
+            kind: "gemini",
+            baseUrl: "https://generativelanguage.googleapis.com",
+            apiKey: "test-key",
+            defaultChatModel: "gemini-2.5-flash",
+          },
+        ],
+      },
+    });
+    const gemini = parsed.llm?.providers.find((p) => p.id === "gemini");
+    expect(gemini?.supportsParallelTools).toBeUndefined();
+  });
+
+  it("rejects non-boolean supportsParallelTools", () => {
+    expect(() =>
+      parseUserConfigFile({
+        version: USER_CONFIG_VERSION,
+        llm: {
+          activeTextProvider: "gemini",
+          activeEmbeddingProvider: "gemini",
+          toolTransport: "auto",
+          providers: [
+            {
+              id: "gemini",
+              kind: "gemini",
+              baseUrl: "https://generativelanguage.googleapis.com",
+              apiKey: "test-key",
+              defaultChatModel: "gemini-2.5-flash",
+              supportsParallelTools: "yes",
+            },
+          ],
+        },
+      }),
+    ).toThrow(/supportsParallelTools/);
+  });
 });

src/config/llm-config.ts

@@ -57,6 +57,14 @@ export type UserLlmProviderEntry = {
   apiKeyHeader?: string;
   supportsTools?: boolean;
   supportsVision?: boolean;
+  /**
+   * Whether the provider supports parallel tool calls in a single
+   * completion.  Absent defaults to `true` for most providers, but
+   * some (e.g. Gemini) emit parallel `tool_calls` without stable
+   * indices — the runtime derives `parallel_tool_calls` from this
+   * flag combined with `agent.maxParallelToolCalls`.
+   */
+  supportsParallelTools?: boolean;
   requestTimeoutMs?: number;
   /**
    * Prompt-caching policy for this provider. Declared in the config
@@ -263,6 +271,17 @@ export function parseLlmProviderEntry(
                 "expected boolean",
               );
             })(),
+    supportsParallelTools:
+      obj.supportsParallelTools === undefined
+        ? undefined
+        : typeof obj.supportsParallelTools === "boolean"
+          ? obj.supportsParallelTools
+          : (() => {
+              throw new ConfigValidationError(
+                `${field}.supportsParallelTools`,
+                "expected boolean",
+              );
+            })(),
     requestTimeoutMs:
       obj.requestTimeoutMs === undefined
         ? undefined

src/llm/provider/registry/provider-registry.test.ts

@@ -62,6 +62,73 @@ describe("ProviderRegistry", () => {
     expect(registry.activeText).toBeInstanceOf(GeminiProvider);
   });
 
+  it("Gemini defaults to supportsParallelTools: false", async () => {
+    const fakeConfig = {
+      ...getConfig(),
+      llm: {
+        activeTextProvider: "gemini",
+        activeEmbeddingProvider: "local-llama-embed",
+        toolTransport: "auto" as const,
+        providers: [
+          {
+            id: "gemini",
+            kind: "gemini",
+            apiKey: "test-key",
+          },
+        ],
+      },
+    } as AtomicAgentConfig;
+
+    const registry = await ProviderRegistry.fromConfig(fakeConfig, {
+      config: fakeConfig,
+      llamaClient: {} as never,
+      getProfile: () => ({}) as never,
+      logger: {
+        debug: () => {},
+        info: () => {},
+        warn: () => {},
+        error: () => {},
+      } as never,
+    });
+
+    const provider = registry.activeText as GeminiProvider;
+    expect(provider.capabilities.supportsParallelTools).toBe(false);
+  });
+
+  it("Gemini respects explicit supportsParallelTools: true override", async () => {
+    const fakeConfig = {
+      ...getConfig(),
+      llm: {
+        activeTextProvider: "gemini",
+        activeEmbeddingProvider: "local-llama-embed",
+        toolTransport: "auto" as const,
+        providers: [
+          {
+            id: "gemini",
+            kind: "gemini",
+            apiKey: "test-key",
+            supportsParallelTools: true,
+          },
+        ],
+      },
+    } as AtomicAgentConfig;
+
+    const registry = await ProviderRegistry.fromConfig(fakeConfig, {
+      config: fakeConfig,
+      llamaClient: {} as never,
+      getProfile: () => ({}) as never,
+      logger: {
+        debug: () => {},
+        info: () => {},
+        warn: () => {},
+        error: () => {},
+      } as never,
+    });
+
+    const provider = registry.activeText as GeminiProvider;
+    expect(provider.capabilities.supportsParallelTools).toBe(true);
+  });
+
   it("rejects unknown provider kind at fromConfig", async () => {
     registerBuiltInProviderKinds();
     const fakeConfig = {

src/llm/provider/registry/provider-types.ts

@@ -36,6 +36,7 @@ export type LlmProviderConfigEntry = {
   apiKeyHeader?: string;
   supportsTools?: boolean;
   supportsVision?: boolean;
+  supportsParallelTools?: boolean;
   requestTimeoutMs?: number;
   promptCache?: "auto" | "off" | "explicit-markers";
   providerPreferences?: Record<string, unknown>;

src/llm/provider/registry/register-built-in-providers.ts

@@ -62,7 +62,8 @@ export function registerBuiltInProviderKinds(): void {
       headers: entry.headers,
       apiKeyHeader: entry.apiKeyHeader,
       supportsVision: entry.supportsVision ?? true,
-      supportsParallelTools: entry.supportsTools ?? true,
+      supportsParallelTools:
+        entry.supportsParallelTools ?? entry.supportsTools ?? true,
       requestTimeoutMs: entry.requestTimeoutMs,
       extraBody: entry.extraBody,
     });
@@ -83,7 +84,8 @@ export function registerBuiltInProviderKinds(): void {
       headers: entry.headers,
       apiKeyHeader: entry.apiKeyHeader,
       supportsVision: entry.supportsVision ?? true,
-      supportsParallelTools: entry.supportsTools ?? true,
+      supportsParallelTools:
+        entry.supportsParallelTools ?? entry.supportsTools ?? true,
       requestTimeoutMs: entry.requestTimeoutMs,
       taggedToolCompatibility: "qwen",
       extraBody: entry.extraBody,
@@ -99,7 +101,8 @@ export function registerBuiltInProviderKinds(): void {
       defaultChatModel: entry.defaultChatModel ?? "openrouter/auto",
       headers: entry.headers,
       supportsVision: entry.supportsVision ?? true,
-      supportsParallelTools: entry.supportsTools ?? true,
+      supportsParallelTools:
+        entry.supportsParallelTools ?? entry.supportsTools ?? true,
       requestTimeoutMs: entry.requestTimeoutMs,
       httpReferer: OPENROUTER_APP_REFERER,
       xTitle: OPENROUTER_APP_TITLE,
@@ -116,7 +119,8 @@ export function registerBuiltInProviderKinds(): void {
       defaultChatModel: entry.defaultChatModel ?? AIMLAPI_DEFAULT_CHAT_MODEL,
       headers: entry.headers,
       supportsVision: entry.supportsVision ?? true,
-      supportsParallelTools: entry.supportsTools ?? true,
+      supportsParallelTools:
+        entry.supportsParallelTools ?? entry.supportsTools ?? true,
       requestTimeoutMs: entry.requestTimeoutMs,
     });
   });
@@ -130,7 +134,11 @@ export function registerBuiltInProviderKinds(): void {
       defaultChatModel: entry.defaultChatModel ?? GEMINI_DEFAULT_CHAT_MODEL,
       headers: entry.headers,
       supportsVision: entry.supportsVision ?? true,
-      supportsParallelTools: entry.supportsTools ?? true,
+      // Gemini does not emit stable indices for parallel tool calls —
+      // the wire still carries parallel_tool_calls: true, but the
+      // model drops or reorders slots, breaking the batch executor.
+      // Users can override with supportsParallelTools: true in config.
+      supportsParallelTools: entry.supportsParallelTools ?? false,
       requestTimeoutMs: entry.requestTimeoutMs,
     });
   });