diff --git a/packages/coding-agent/src/modes/interactive-mode.ts b/packages/coding-agent/src/modes/interactive-mode.ts
index 4a4e8f387..e78b33ac2 100644
--- a/packages/coding-agent/src/modes/interactive-mode.ts
+++ b/packages/coding-agent/src/modes/interactive-mode.ts
@@ -611,17 +611,20 @@ export class InteractiveMode implements InteractiveModeContext {
 		await this.#reconcileModeFromSession();
 
 		// Brand-new sessions optionally start in plan mode when the user has made
-		// it the startup default. "Brand-new" is keyed off the session having no
-		// prior entries — not the CLI resume flags — so `omp --continue` (or
-		// auto-resume) that finds no recent session and creates a fresh one still
-		// honors the default, while a session with restored history keeps whatever
-		// mode #reconcileModeFromSession just reconciled. Scoped to launch (not the
-		// switch reconciler above) so /new and the plan-approval → execution handoff
-		// clear never get dragged back into plan mode. #enterPlanMode is idempotent
-		// and self-guards against an already-active plan/goal mode; it does not check
-		// plan.enabled itself.
+		// it the startup default. "Brand-new" means no prior *conversation*: a fresh
+		// session created via the SDK already carries startup metadata entries
+		// (model_change / thinking_level_change / service_tier_change appended before
+		// init), so key off message entries rather than entry count. This way `omp
+		// --continue` (or auto-resume) that finds no recent session and creates a
+		// fresh one still honors the default, while a session with restored
+		// conversation keeps whatever mode #reconcileModeFromSession just reconciled.
+		// Scoped to launch (not the switch reconciler above) so /new and the
+		// plan-approval → execution handoff clear never get dragged back into plan
+		// mode. #enterPlanMode is idempotent and self-guards against an already-active
+		// plan/goal mode; it does not check plan.enabled itself.
+		const hasPriorConversation = this.sessionManager.getEntries().some(entry => entry.type === "message");
 		if (
-			this.sessionManager.getEntries().length === 0 &&
+			!hasPriorConversation &&
 			this.session.settings.get("plan.defaultOnStartup") &&
 			this.session.settings.get("plan.enabled")
 		) {
diff --git a/packages/coding-agent/test/interactive-mode-default-plan-mode.test.ts b/packages/coding-agent/test/interactive-mode-default-plan-mode.test.ts
index e1dbacb7c..66ccc3107 100644
--- a/packages/coding-agent/test/interactive-mode-default-plan-mode.test.ts
+++ b/packages/coding-agent/test/interactive-mode-default-plan-mode.test.ts
@@ -116,11 +116,11 @@ describe("InteractiveMode plan.defaultOnStartup", () => {
 		expect(session?.getPlanModeState()).toBeUndefined();
 	});
 
-	it("does not enter plan mode when the session has restored history", async () => {
-		// A genuinely resumed session has prior entries; gating on getEntries()
-		// (not the CLI resume flag) means a `--continue` that created a *fresh*,
-		// empty session still gets the startup default (the "enters" case above),
-		// while one with restored history is left in its reconciled mode.
+	it("does not enter plan mode when the session has restored conversation", async () => {
+		// A genuinely resumed session has prior conversation messages. Gating on
+		// message entries (not the CLI resume flag) means a `--continue` that
+		// created a *fresh* session still gets the startup default (above), while
+		// one with restored conversation is left in its reconciled mode.
 		const created = createHarness(Settings.isolated({ "plan.defaultOnStartup": true, "compaction.enabled": false }));
 		created.sessionManager.appendMessage({ role: "user", content: "prior turn", timestamp: Date.now() });
 
@@ -130,6 +130,21 @@ describe("InteractiveMode plan.defaultOnStartup", () => {
 		expect(session?.getPlanModeState()).toBeUndefined();
 	});
 
+	it("enters plan mode for a fresh session that carries only startup metadata", async () => {
+		// createAgentSession appends model_change / thinking_level_change for a
+		// brand-new session before init(); those are not conversation history, so
+		// the startup default must still apply (regression: gating on entry count
+		// instead of message entries skipped plan mode for every real new session).
+		const created = createHarness(Settings.isolated({ "plan.defaultOnStartup": true, "compaction.enabled": false }));
+		created.sessionManager.appendModelChange("anthropic/claude-sonnet-4-5");
+		created.sessionManager.appendThinkingLevelChange("medium");
+
+		await created.init({ suppressWelcomeIntro: true });
+
+		expect(created.planModeEnabled).toBe(true);
+		expect(session?.getPlanModeState()).toMatchObject({ enabled: true });
+	});
+
 	it("does not enter plan mode when plan mode is globally disabled", async () => {
 		const created = createHarness(
 			Settings.isolated({ "plan.defaultOnStartup": true, "plan.enabled": false, "compaction.enabled": false }),