diff --git a/src/features/team-mode/team-layout-tmux/resolve-caller-tmux-session.test.ts b/src/features/team-mode/team-layout-tmux/resolve-caller-tmux-session.test.ts
new file mode 100644
index 000000000..492b6847c
--- /dev/null
+++ b/src/features/team-mode/team-layout-tmux/resolve-caller-tmux-session.test.ts
@@ -0,0 +1,106 @@
+/// <reference types="bun-types" />
+
+import { afterEach, beforeEach, describe, expect, test } from "bun:test"
+import { chmod, mkdtemp, readFile, rm, writeFile } from "node:fs/promises"
+import { tmpdir } from "node:os"
+import path from "node:path"
+
+import { resolveCallerTmuxSession } from "./resolve-caller-tmux-session"
+
+type TmuxStub = {
+	tmuxPath: string
+	logPath: string
+}
+
+const temporaryDirectories: string[] = []
+
+function shellSingleQuote(value: string): string {
+	return `'${value.split("'").join(`'"'"'`)}'`
+}
+
+async function createTmuxStub(options: { stdout: string; exitCode: number }): Promise<TmuxStub> {
+	const directory = await mkdtemp(path.join(tmpdir(), "resolve-caller-tmux-session-"))
+	temporaryDirectories.push(directory)
+
+	const logPath = path.join(directory, "tmux.log")
+	const tmuxPath = path.join(directory, "tmux")
+	const script = [
+		"#!/bin/sh",
+		`printf '%s\\n' \"$@\" >> ${shellSingleQuote(logPath)}`,
+		`printf '%s' ${shellSingleQuote(options.stdout)}`,
+		`exit ${options.exitCode}`,
+	].join("\n")
+
+	await writeFile(tmuxPath, script)
+	await chmod(tmuxPath, 0o755)
+
+	return { tmuxPath, logPath }
+}
+
+async function readLogLines(logPath: string): Promise<string[]> {
+	try {
+		const content = await readFile(logPath, "utf8")
+		return content.split("\n").filter((line) => line.length > 0)
+	} catch {
+		return []
+	}
+}
+
+beforeEach(() => {
+	delete process.env.TMUX_PANE
+})
+
+afterEach(async () => {
+	await Promise.all(temporaryDirectories.splice(0).map(async (directory) => rm(directory, { recursive: true, force: true })))
+})
+
+describe("resolveCallerTmuxSession", () => {
+	test("#given TMUX_PANE unset #when resolve runs #then returns null and makes no tmux calls", async () => {
+		// given
+		const stub = await createTmuxStub({ stdout: "$7", exitCode: 0 })
+
+		// when
+		const result = await resolveCallerTmuxSession(stub.tmuxPath)
+
+		// then
+		expect(result).toBeNull()
+		expect(await readLogLines(stub.logPath)).toHaveLength(0)
+	})
+
+	test("#given TMUX_PANE=%42 and display returns '$7' #when resolve runs #then returns { sessionId: '$7' }", async () => {
+		// given
+		process.env.TMUX_PANE = "%42"
+		const stub = await createTmuxStub({ stdout: "$7", exitCode: 0 })
+
+		// when
+		const result = await resolveCallerTmuxSession(stub.tmuxPath)
+
+		// then
+		expect(result).toEqual({ sessionId: "$7" })
+		expect(await readLogLines(stub.logPath)).toEqual(["display", "-p", "-F", "#{session_id}", "-t", "%42"])
+	})
+
+	test("#given TMUX_PANE=%42 and display returns 'garbage' #when resolve runs #then returns null", async () => {
+		// given
+		process.env.TMUX_PANE = "%42"
+		const stub = await createTmuxStub({ stdout: "garbage", exitCode: 0 })
+
+		// when
+		const result = await resolveCallerTmuxSession(stub.tmuxPath)
+
+		// then
+		expect(result).toBeNull()
+	})
+
+	test("#given TMUX_PANE=%42 and display exits non-success #when resolve runs #then returns null", async () => {
+		// given
+		process.env.TMUX_PANE = "%42"
+		const stub = await createTmuxStub({ stdout: "$7", exitCode: 1 })
+
+		// when
+		const result = await resolveCallerTmuxSession(stub.tmuxPath)
+
+		// then
+		expect(result).toBeNull()
+	})
+})
diff --git a/src/features/team-mode/team-layout-tmux/resolve-caller-tmux-session.ts b/src/features/team-mode/team-layout-tmux/resolve-caller-tmux-session.ts
new file mode 100644
index 000000000..3766a5d99
--- /dev/null
+++ b/src/features/team-mode/team-layout-tmux/resolve-caller-tmux-session.ts
@@ -0,0 +1,26 @@
+import { runTmuxCommand } from "../../../shared/tmux"
+
+type ResolvedCallerTmuxSession = {
+	sessionId: string
+}
+
+const TMUX_SESSION_ID_PATTERN = /^\$[0-9]+$/
+
+export async function resolveCallerTmuxSession(tmuxPath: string): Promise<ResolvedCallerTmuxSession | null> {
+	const callerPaneId = process.env.TMUX_PANE
+	if (!callerPaneId) {
+		return null
+	}
+
+	const result = await runTmuxCommand(tmuxPath, ["display", "-p", "-F", "#{session_id}", "-t", callerPaneId])
+	if (!result.success) {
+		return null
+	}
+
+	const sessionId = result.output.trim()
+	if (!TMUX_SESSION_ID_PATTERN.test(sessionId)) {
+		return null
+	}
+
+	return { sessionId }
+}