Fix Claude binary resolution for replace-mode command override

isAvailable() honored runtimeSettings.command.mode === "replace" but
resolveClaudeBinary() only looked for `claude` on PATH. Users with a
custom claude wrapper and no `claude` itself on PATH passed the
availability check and then failed at session creation with "Claude
binary not found".

resolveClaudeBinary now mirrors isAvailable: if the runtime command is
in replace mode, look up the override binary first.

packages/server/src/server/agent/providers/claude/agent.test.ts

@@ -1,7 +1,8 @@
-import { describe, expect, test, vi } from "vitest";
+import { afterEach, describe, expect, test, vi } from "vitest";
 import type { SDKMessage } from "@anthropic-ai/claude-agent-sdk";
 
 import { createTestLogger } from "../../../../test-utils/test-logger.js";
+import * as executableUtils from "../../../../utils/executable.js";
 import {
   ClaudeAgentClient,
   convertClaudeHistoryEntry,
@@ -14,6 +15,10 @@ interface TestClaudeSession {
   convertUsage(message: SDKMessage): AgentUsage | undefined;
 }
 
+afterEach(() => {
+  vi.restoreAllMocks();
+});
+
 describe("convertClaudeHistoryEntry", () => {
   test("maps user tool results to timeline items", () => {
     const toolUseId = "toolu_test";
@@ -369,6 +374,59 @@ describe("ClaudeAgentClient.listModels", () => {
   });
 });
 
+describe("ClaudeAgentClient binary resolution", () => {
+  const logger = createTestLogger();
+
+  test("uses the replace-command override binary when claude is not on PATH", async () => {
+    const customClaudePath = "/path/to/custom-claude";
+    vi.spyOn(executableUtils, "findExecutable").mockImplementation(async (name: string) => {
+      if (name === "claude") {
+        return null;
+      }
+      if (name === customClaudePath) {
+        return customClaudePath;
+      }
+      return null;
+    });
+
+    const queryReturn = vi.fn();
+    queryReturn.mockResolvedValue(undefined);
+    const queryFactory = vi.fn(() => ({
+      close: vi.fn(),
+      return: queryReturn,
+    }));
+
+    const client = new ClaudeAgentClient({
+      logger,
+      queryFactory,
+      runtimeSettings: {
+        command: {
+          mode: "replace",
+          argv: [customClaudePath],
+        },
+      },
+    });
+    const session = await client.createSession({
+      provider: "claude",
+      cwd: process.cwd(),
+    });
+
+    await expect(
+      (
+        session as unknown as {
+          ensureQuery(): Promise<unknown>;
+        }
+      ).ensureQuery(),
+    ).resolves.toBeDefined();
+
+    expect(queryFactory.mock.calls[0]?.[0].options.pathToClaudeCodeExecutable).toBe(
+      customClaudePath,
+    );
+
+    await session.close();
+  });
+});
+
 describe("normalizeClaudeAskUserQuestionUpdatedInput", () => {
   test("maps frontend header-keyed answers to Claude question text keys", () => {
     expect(

packages/server/src/server/agent/providers/claude/agent.ts

@@ -1169,7 +1169,7 @@ export class ClaudeAgentClient implements AgentClient {
     this.logger = options.logger.child({ module: "agent", provider: "claude" });
     this.runtimeSettings = options.runtimeSettings;
     this.queryFactory = options.queryFactory;
-    this.resolveBinary = options.resolveBinary ?? resolveClaudeBinary;
+    this.resolveBinary = options.resolveBinary ?? (() => resolveClaudeBinary(this.runtimeSettings));
   }
 
   async createSession(
@@ -1296,7 +1296,15 @@ export class ClaudeAgentClient implements AgentClient {
   }
 }
 
-async function resolveClaudeBinary(): Promise<string> {
+async function resolveClaudeBinary(runtimeSettings?: ProviderRuntimeSettings): Promise<string> {
+  const command = runtimeSettings?.command;
+  if (command?.mode === "replace") {
+    const foundOverride = await findExecutable(command.argv[0]);
+    if (foundOverride) {
+      return foundOverride;
+    }
+  }
+
   const found = await findExecutable("claude");
   if (found) {
     return found;