diff --git a/packages/coding-agent/src/dap/session.ts b/packages/coding-agent/src/dap/session.ts
index 91daa3eb9..4ac44fb92 100644
--- a/packages/coding-agent/src/dap/session.ts
+++ b/packages/coding-agent/src/dap/session.ts
@@ -961,11 +961,13 @@ export class DapSessionManager {
 		timeoutMs: number = 30_000,
 	): Promise<{ snapshot: DapSessionSummary; threads: DapThread[] }> {
 		const anchor = this.#touchActiveSession();
-		// A js-debug launch is a session tree: the root is a threadless launcher
-		// and each real thread lives in a child (main script, `[worker N]`, …).
-		// Querying only the active session would surface just one child's threads,
-		// so aggregate across every live thread-owning session in the tree.
-		const targets = this.#threadOwningSessions(anchor);
+		// A js-debug launch is a session tree: the root may be a threadless
+		// launcher while each real thread lives in a child (main script,
+		// `[worker N]`, …), and other adapters keep every thread on the root.
+		// Querying only the active session would surface just one session's
+		// threads, so aggregate across the whole live tree. No topology guess:
+		// a threadless launcher simply returns no threads (or an error we skip).
+		const targets = this.#liveTreeSessions(anchor);
 		const merged: DapThread[] = [];
 		const seen = new Set<string>();
 		for (const target of targets) {
@@ -1767,24 +1769,16 @@ export class DapSessionManager {
 	}
 
 	/**
-	 * Live sessions in `session`'s tree that can own threads. The threadless
-	 * root launcher (a js-debug coordinator with live children) is dropped when
-	 * any real child is alive, but kept as a last resort so a collapsed tree
-	 * still has a target.
+	 * Live (non-terminated, connected) sessions in `session`'s tree, or the
+	 * session itself when the tree has collapsed. Used to fan `threads` out
+	 * across the whole tree; a threadless session just reports no threads, so
+	 * this makes no assumption about which node owns them.
 	 */
-	#threadOwningSessions(session: DapSession): DapSession[] {
+	#liveTreeSessions(session: DapSession): DapSession[] {
 		const live = this.#getTreeSessions(session).filter(
 			candidate => candidate.status !== "terminated" && candidate.client.isAlive(),
 		);
-		if (live.length === 0) return [session];
-		const nonLauncher = live.filter(candidate => !this.#isLauncherSession(candidate, live));
-		return nonLauncher.length > 0 ? nonLauncher : live;
-	}
-
-	/** A root session that has spawned a still-live child is a threadless launcher. */
-	#isLauncherSession(session: DapSession, live: DapSession[]): boolean {
-		if (session.parentSessionId) return false;
-		return live.some(candidate => candidate.parentSessionId === session.id);
+		return live.length > 0 ? live : [session];
 	}
 
 	#touchSessionAndAncestors(session: DapSession): void {
diff --git a/packages/coding-agent/test/debug/dap-multi-session.test.ts b/packages/coding-agent/test/debug/dap-multi-session.test.ts
index 1e4fa19a5..655b0605a 100644
--- a/packages/coding-agent/test/debug/dap-multi-session.test.ts
+++ b/packages/coding-agent/test/debug/dap-multi-session.test.ts
@@ -223,7 +223,9 @@ describe("DAP multi-session debugging", () => {
 		expect(active?.parentSessionId).toBeDefined();
 		expect(threads.threads).toEqual([{ id: 7, name: "target.js" }]);
 		expect(child.requests.filter(request => request.command === "threads")).toHaveLength(1);
-		expect(root.requests.filter(request => request.command === "threads")).toHaveLength(0);
+		// The root is queried too (no topology guess); here it just echoes the
+		// same thread, which dedupes away.
+		expect(root.requests.filter(request => request.command === "threads")).toHaveLength(1);
 
 		await manager.terminate(undefined, 100);
 	});
@@ -262,12 +264,18 @@ describe("DAP multi-session debugging", () => {
 	});
 
 	it("keeps focus on the stopped script child when a worker attaches later", async () => {
-		const root = new FakeDapClient({
-			name: "script.mts",
-			type: "pwa-node",
-			__pendingTargetId: "main",
-			program: "/tmp/script.mts",
-		});
+		const root = new FakeDapClient(
+			{
+				name: "script.mts",
+				type: "pwa-node",
+				__pendingTargetId: "main",
+				program: "/tmp/script.mts",
+			},
+			"launch",
+			true,
+			// Threadless launcher: it answers `threads` with an empty list.
+			{ threads: [] },
+		);
 		// The script child stops on entry (thread 1), then a worker session
 		// attaches afterwards via a late reverse `startDebugging`.
 		const main = new FakeDapClient(undefined, "launch", true, {
@@ -308,14 +316,15 @@ describe("DAP multi-session debugging", () => {
 
 		// `threads` must surface every live thread across the tree, not just one.
 		const threads = await manager.threads(undefined, 1_000);
+		expect(threads.threads).toHaveLength(2);
 		expect(threads.threads).toEqual(
 			expect.arrayContaining([
 				{ id: 1, name: "script.mts" },
 				{ id: 1, name: "[worker 1]" },
 			]),
 		);
-		// The threadless launcher is never queried while real children are live.
-		expect(root.requests.filter(request => request.command === "threads")).toHaveLength(0);
+		// The launcher is still queried, but being threadless it contributes none.
+		expect(root.requests.filter(request => request.command === "threads")).toHaveLength(1);
 
 		await manager.terminate(undefined, 1_000);
 	});