diff --git a/docs/adapters/claude-local.md b/docs/adapters/claude-local.md
index 43d1b0e49bc..e1d09f0ca3f 100644
--- a/docs/adapters/claude-local.md
+++ b/docs/adapters/claude-local.md
@@ -37,6 +37,10 @@ subscription quota exhaustion merely because ACP labels them `limit`.
 | `maxTurnsPerRun` | number | No | Max agentic turns per heartbeat (defaults to `300`) |
 | `dangerouslySkipPermissions` | boolean | No | Skip permission prompts (default: `true`); required for headless runs where interactive approval is impossible |
 
+On the CLI engine, version and `--effort` capability probes have a bounded
+20-second budget when `timeoutSec` is zero or unset. A positive run timeout below
+20 seconds also limits these probes, with a minimum probe budget of one second.
+
 ## Default model
 
 An omitted, empty, or whitespace-only `model` uses Claude Opus 5
diff --git a/packages/adapters/claude-local/src/server/cli-capabilities.test.ts b/packages/adapters/claude-local/src/server/cli-capabilities.test.ts
new file mode 100644
index 00000000000..092cc5d8a89
--- /dev/null
+++ b/packages/adapters/claude-local/src/server/cli-capabilities.test.ts
@@ -0,0 +1,42 @@
+import { afterEach, describe, expect, it } from "vitest";
+import { chmodSync, mkdtempSync, rmSync, writeFileSync } from "node:fs";
+import os from "node:os";
+import path from "node:path";
+import {
+  claudeCommandSupportsEffortFlag,
+  readClaudeCommandVersion,
+  resetClaudeCliCapabilitiesCacheForTests,
+} from "./cli-capabilities.js";
+
+const directories: string[] = [];
+
+afterEach(() => {
+  resetClaudeCliCapabilitiesCacheForTests();
+  for (const directory of directories.splice(0)) rmSync(directory, { recursive: true, force: true });
+});
+
+function slowClaude() {
+  const cwd = mkdtempSync(path.join(os.tmpdir(), "paperclip-slow-claude-"));
+  directories.push(cwd);
+  const command = path.join(cwd, "claude");
+  writeFileSync(command, `#!${process.execPath}\nsetTimeout(() => {
+  console.log(process.argv.includes("--version") ? "2.1.284 (test CLI)" : "Usage: claude --effort <level>");
+}, 1500);\n`);
+  chmodSync(command, 0o755);
+  return { runId: "capability-probe", command, target: null, cwd, env: {}, graceSec: 1 };
+}
+
+// This fixture is a real executable. Windows does not use POSIX shebang files.
+describe.skipIf(process.platform === "win32")("Claude CLI capability probe budgets", () => {
+  it("allows a slow version and effort probe with an unlimited run timeout", async () => {
+    const input = { ...slowClaude(), timeoutSec: 0 };
+    await expect(readClaudeCommandVersion(input)).resolves.toBe("2.1.284");
+    await expect(claudeCommandSupportsEffortFlag(input)).resolves.toBe(true);
+  }, 30_000);
+
+  it("retains an explicit shorter positive timeout", async () => {
+    const input = { ...slowClaude(), timeoutSec: 1 };
+    await expect(readClaudeCommandVersion(input)).resolves.toBeNull();
+    await expect(claudeCommandSupportsEffortFlag(input)).resolves.toBeNull();
+  }, 30_000);
+});
diff --git a/packages/adapters/claude-local/src/server/cli-capabilities.ts b/packages/adapters/claude-local/src/server/cli-capabilities.ts
index dec74c2f384..f20c46d7c91 100644
--- a/packages/adapters/claude-local/src/server/cli-capabilities.ts
+++ b/packages/adapters/claude-local/src/server/cli-capabilities.ts
@@ -85,7 +85,7 @@ async function probeClaudeCommandVersion(input: {
     {
       cwd: input.cwd,
       env: input.env,
-      timeoutSec: Math.max(1, Math.min(input.timeoutSec, 20)),
+      timeoutSec: input.timeoutSec > 0 ? Math.max(1, Math.min(input.timeoutSec, 20)) : 20,
       graceSec: Math.max(1, Math.min(input.graceSec, 5)),
       onLog: async () => {},
     },
@@ -127,7 +127,7 @@ async function probeClaudeCommandSupportsEffortFlag(input: {
     {
       cwd: input.cwd,
       env: input.env,
-      timeoutSec: Math.max(1, Math.min(input.timeoutSec, 20)),
+      timeoutSec: input.timeoutSec > 0 ? Math.max(1, Math.min(input.timeoutSec, 20)) : 20,
       graceSec: Math.max(1, Math.min(input.graceSec, 5)),
       onLog: async () => {},
     },