feat(coding-agent): Add sessionDir support in settings.json (#2598)

Users can now set sessionDir in global or project settings.json instead
of passing --session-dir on every invocation. CLI flag takes precedence,
then settings.json, then extension hooks.

Closes #2429

Co-authored-by: Sam Collins <81678+smcllns@users.noreply.github.com>
Co-authored-by: Mario Zechner <badlogicgames@gmail.com>

packages/coding-agent/test/settings-manager.test.ts

@@ -288,4 +288,25 @@ describe("SettingsManager", () => {
 			expect(savedSettings.theme).toBe("light");
 		});
 	});
+
+	describe("getSessionDir", () => {
+		it("should return undefined when not set", () => {
+			writeFileSync(join(agentDir, "settings.json"), JSON.stringify({ theme: "dark" }));
+			const manager = SettingsManager.create(projectDir, agentDir);
+			expect(manager.getSessionDir()).toBeUndefined();
+		});
+
+		it("should return global sessionDir", () => {
+			writeFileSync(join(agentDir, "settings.json"), JSON.stringify({ sessionDir: "/tmp/sessions" }));
+			const manager = SettingsManager.create(projectDir, agentDir);
+			expect(manager.getSessionDir()).toBe("/tmp/sessions");
+		});
+
+		it("should return project sessionDir, overriding global", () => {
+			writeFileSync(join(agentDir, "settings.json"), JSON.stringify({ sessionDir: "/global/sessions" }));
+			writeFileSync(join(projectDir, ".pi", "settings.json"), JSON.stringify({ sessionDir: "./sessions" }));
+			const manager = SettingsManager.create(projectDir, agentDir);
+			expect(manager.getSessionDir()).toBe("./sessions");
+		});
+	});
 });