diff --git a/src/hooks/cmux-notification-adapter.test.ts b/src/hooks/cmux-notification-adapter.test.ts
index f260cfb11..1e5308ca6 100644
--- a/src/hooks/cmux-notification-adapter.test.ts
+++ b/src/hooks/cmux-notification-adapter.test.ts
@@ -1,4 +1,7 @@
 import { describe, expect, test } from "bun:test"
+import { chmodSync, mkdtempSync, rmSync, writeFileSync } from "node:fs"
+import { tmpdir } from "node:os"
+import { join } from "node:path"
 import {
   createCmuxNotificationAdapter,
   type CmuxNotifyCommandResult,
@@ -139,4 +142,48 @@ describe("cmux notification adapter", () => {
     expect(secondDelivered).toBe(false)
     expect(callCount).toBe(1)
   })
+
+  test("returns promptly on timeout when cmux process ignores TERM", async () => {
+    if (process.platform === "win32") {
+      return
+    }
+
+    const tempDirectory = mkdtempSync(join(tmpdir(), "cmux-notify-timeout-"))
+    const fakeCmuxPath = join(tempDirectory, "cmux")
+    const slowCmuxScript = `#!/bin/sh
+if [ "$1" = "notify" ]; then
+  trap '' TERM
+  /bin/sleep 1
+  exit 0
+fi
+
+exit 1
+`
+
+    writeFileSync(fakeCmuxPath, slowCmuxScript)
+    chmodSync(fakeCmuxPath, 0o755)
+
+    const runtime = createResolvedMultiplexer()
+    runtime.cmux.path = fakeCmuxPath
+
+    try {
+      const adapter = createCmuxNotificationAdapter({
+        runtime,
+        environment: {
+          PATH: tempDirectory,
+        },
+        timeoutMs: 40,
+      })
+
+      const startedAt = Date.now()
+      const delivered = await adapter.send("OpenCode", "Task complete")
+      const elapsedMs = Date.now() - startedAt
+
+      expect(delivered).toBe(false)
+      expect(adapter.hasDowngraded()).toBe(true)
+      expect(elapsedMs).toBeLessThan(500)
+    } finally {
+      rmSync(tempDirectory, { recursive: true, force: true })
+    }
+  })
 })
diff --git a/src/hooks/cmux-notification-adapter.ts b/src/hooks/cmux-notification-adapter.ts
index acbd3b4f4..8975977b7 100644
--- a/src/hooks/cmux-notification-adapter.ts
+++ b/src/hooks/cmux-notification-adapter.ts
@@ -83,7 +83,20 @@ async function runCmuxNotifyCommand(input: {
     clearTimeout(timeoutHandle)
   }
 
-  const exitCode = timedOut ? null : await proc.exited.catch(() => null)
+  if (timedOut) {
+    // Do not await stdout/stderr after timeout: a process that ignores TERM
+    // may keep pipes open and block fallback completion.
+    void proc.exited.catch(() => {})
+
+    return {
+      exitCode: null,
+      stdout: "",
+      stderr: "",
+      timedOut: true,
+    }
+  }
+
+  const exitCode = await proc.exited.catch(() => null)
   const stdout = await new Response(proc.stdout).text().catch(() => "")
   const stderr = await new Response(proc.stderr).text().catch(() => "")
 
diff --git a/src/tools/interactive-bash/tmux-path-resolver.test.ts b/src/tools/interactive-bash/tmux-path-resolver.test.ts
index b3121be46..46e0122b3 100644
--- a/src/tools/interactive-bash/tmux-path-resolver.test.ts
+++ b/src/tools/interactive-bash/tmux-path-resolver.test.ts
@@ -83,6 +83,10 @@ describe("tmux-path-resolver probe environment", () => {
   })
 
   test("probeCmuxNotificationCapability returns promptly after probe timeout", async () => {
+    if (process.platform === "win32") {
+      return
+    }
+
     const tempDirectory = mkdtempSync(join(tmpdir(), "tmux-path-resolver-timeout-"))
     const fakeCmuxPath = join(tempDirectory, "cmux")
     const slowCmuxScript = `#!/bin/sh
diff --git a/src/tools/interactive-bash/tools.test.ts b/src/tools/interactive-bash/tools.test.ts
new file mode 100644
index 000000000..9bac6a39a
--- /dev/null
+++ b/src/tools/interactive-bash/tools.test.ts
@@ -0,0 +1,66 @@
+import { afterEach, describe, expect, test } from "bun:test"
+import {
+  resetResolvedMultiplexerRuntimeForTesting,
+  setResolvedMultiplexerRuntime,
+  type ResolvedMultiplexer,
+} from "../../shared/tmux"
+import { createInteractiveBashTool, interactive_bash } from "./tools"
+
+const mockToolContext = {
+  sessionID: "test-session",
+  messageID: "msg-1",
+  agent: "test-agent",
+  abort: new AbortController().signal,
+}
+
+function createTmuxEnabledRuntime(): ResolvedMultiplexer {
+  return {
+    platform: process.platform,
+    mode: "tmux-only",
+    paneBackend: "tmux",
+    notificationBackend: "desktop",
+    tmux: {
+      path: "/usr/bin/tmux",
+      reachable: true,
+      insideEnvironment: true,
+      paneId: "%1",
+      explicitDisable: false,
+    },
+    cmux: {
+      path: null,
+      reachable: false,
+      notifyCapable: false,
+      socketPath: undefined,
+      endpointType: "missing",
+      workspaceId: undefined,
+      surfaceId: undefined,
+      hintStrength: "none",
+      explicitDisable: false,
+    },
+  }
+}
+
+describe("interactive_bash runtime resolution", () => {
+  afterEach(() => {
+    resetResolvedMultiplexerRuntimeForTesting()
+  })
+
+  test("createInteractiveBashTool without runtime resolves current runtime on execute", async () => {
+    resetResolvedMultiplexerRuntimeForTesting()
+    const tool = createInteractiveBashTool()
+    setResolvedMultiplexerRuntime(createTmuxEnabledRuntime())
+
+    const result = await tool.execute({ tmux_command: "capture-pane -p" }, mockToolContext)
+
+    expect(result).not.toContain("pane control is unavailable")
+  })
+
+  test("interactive_bash singleton resolves current runtime on execute", async () => {
+    resetResolvedMultiplexerRuntimeForTesting()
+    setResolvedMultiplexerRuntime(createTmuxEnabledRuntime())
+
+    const result = await interactive_bash.execute({ tmux_command: "capture-pane -p" }, mockToolContext)
+
+    expect(result).not.toContain("pane control is unavailable")
+  })
+})
diff --git a/src/tools/interactive-bash/tools.ts b/src/tools/interactive-bash/tools.ts
index 6421e018c..49198cb20 100644
--- a/src/tools/interactive-bash/tools.ts
+++ b/src/tools/interactive-bash/tools.ts
@@ -54,9 +54,7 @@ export function tokenizeCommand(cmd: string): string[] {
 }
 
 export function createInteractiveBashTool(
-  runtime: ResolvedMultiplexer =
-    getResolvedMultiplexerRuntime()
-    ?? createDisabledMultiplexerRuntime(),
+  runtime?: ResolvedMultiplexer,
 ): ToolDefinition {
   return tool({
     description: INTERACTIVE_BASH_DESCRIPTION,
@@ -65,8 +63,13 @@ export function createInteractiveBashTool(
     },
     execute: async (args) => {
       try {
-        if (runtime.paneBackend !== "tmux") {
-          return `Error: interactive_bash is TMUX-only and pane control is unavailable in '${runtime.mode}' runtime.`
+        const resolvedRuntime =
+          runtime
+          ?? getResolvedMultiplexerRuntime()
+          ?? createDisabledMultiplexerRuntime()
+
+        if (resolvedRuntime.paneBackend !== "tmux") {
+          return `Error: interactive_bash is TMUX-only and pane control is unavailable in '${resolvedRuntime.mode}' runtime.`
         }
 
         const tmuxPath = await getTmuxPath()