fix(coding-agent): pair checkpoint/rewind for restricted sessions too

The !restrictToolNames guard on the pairing blocks was wrong: a restricted
session with tools:[checkpoint] passes isToolAllowed (requestedTools is
defined) but the pairing is skipped, stranding the agent without rewind.
Remove the guard — this is a safety pairing, not a convenience widening.
Added restricted-session tests in both createTools and SDK active-set paths.

packages/coding-agent/src/sdk.ts

@@ -2796,8 +2796,10 @@ export async function createAgentSession(options: CreateAgentSessionOptions = {}
 		// Checkpoint and rewind are a pair: `createTools` auto-includes the sister
 		// tool in the registry, but an explicit `toolNames` list would otherwise
 		// drop it from the ACTIVE set — leaving the agent able to checkpoint but
-		// unable to rewind (or vice versa). Mirror the pairing here.
-		if (!restrictToolNames && explicitlyRequestedToolNames) {
+		// unable to rewind (or vice versa). Mirror the pairing here. Unlike the
+		// manage_skill/learn mirror above, this is a safety pairing — it applies
+		// to restricted sessions too.
+		if (explicitlyRequestedToolNames) {
 			if (builtInToolNames.includes("checkpoint") && !explicitlyRequestedToolNames.includes("rewind")) {
 				explicitlyRequestedToolNames.push("rewind");
 			} else if (builtInToolNames.includes("rewind") && !explicitlyRequestedToolNames.includes("checkpoint")) {

packages/coding-agent/src/tools/index.ts

@@ -505,8 +505,9 @@ export async function createTools(session: ToolSession, toolNames?: string[]): P
 	// Checkpoint and rewind are a pair: listing one without the other strands
 	// the agent (it can checkpoint but not rewind, or vice versa). Auto-include
 	// the sister tool so a one-sided frontmatter `tools:` entry still works.
-	// Like the AST/auto-learn siblings below, restricted callers own the list.
-	if (requestedTools && !restrictToolNames && session.settings.get("checkpoint.enabled")) {
+	// Unlike the AST/auto-learn convenience auto-includes below, this is a
+	// safety pairing — it applies to restricted sessions too.
+	if (requestedTools && session.settings.get("checkpoint.enabled")) {
 		if (requestedTools.includes("checkpoint") && !requestedTools.includes("rewind")) {
 			requestedTools.push("rewind");
 		} else if (requestedTools.includes("rewind") && !requestedTools.includes("checkpoint")) {

packages/coding-agent/test/sdk-autolearn-active-tools.test.ts

@@ -122,4 +122,23 @@ describe("createAgentSession auto-learn tool activation", () => {
 		expect(names).toContain("checkpoint");
 		expect(names).toContain("rewind");
 	});
+
+	it("activates checkpoint and rewind in a restricted session with one-sided toolNames", async () => {
+		const { session } = await createAgentSession({
+			cwd: registryDir,
+			agentDir: registryDir,
+			modelRegistry,
+			sessionManager: SessionManager.inMemory(),
+			settings: Settings.isolated({ "checkpoint.enabled": true }),
+			model: getBundledModel("openai", "gpt-4o-mini"),
+			disableExtensionDiscovery: true,
+			toolNames: ["checkpoint"],
+			requireYieldTool: true,
+			restrictToolNames: true,
+		});
+		sessions.push(session);
+		const names = session.getActiveToolNames();
+		expect(names).toContain("checkpoint");
+		expect(names).toContain("rewind");
+	});
 });

packages/coding-agent/test/tools/index.test.ts

@@ -397,6 +397,21 @@ describe("createTools", () => {
 		expect(names).not.toContain("rewind");
 	});
 
+	it("auto-pairs checkpoint/rewind in a restricted subagent with one-sided list", async () => {
+		const names = (
+			await createTools(
+				createTestSession({
+					taskDepth: 1,
+					restrictToolNames: true,
+					settings: createSettingsWithOverrides({ "checkpoint.enabled": true }),
+				}),
+				["checkpoint"],
+			)
+		).map(t => t.name);
+		expect(names).toContain("checkpoint");
+		expect(names).toContain("rewind");
+	});
+
 	it("HIDDEN_TOOLS contains yield and goal", () => {
 		expect(Object.keys(HIDDEN_TOOLS).sort()).toEqual(["goal", "yield"]);
 	});