fix(coding-agent): handle missing export themes

closes #5596

packages/coding-agent/CHANGELOG.md

@@ -8,6 +8,7 @@
 
 ### Fixed
 
+- Fixed `/share` and `/export` HTML exports to use the active fallback theme when the configured custom theme no longer exists ([#5596](https://github.com/earendil-works/pi/issues/5596)).
 - Fixed custom fallback model IDs with `:<thinking>` suffixes to preserve the requested thinking level when the provider template model does not advertise reasoning ([#5552](https://github.com/earendil-works/pi/issues/5552)).
 
 ## [0.79.1] - 2026-06-09

packages/coding-agent/src/core/agent-session.ts

@@ -33,7 +33,7 @@ import {
 	resetApiProviders,
 	streamSimple,
 } from "@earendil-works/pi-ai";
-import { theme } from "../modes/interactive/theme/theme.ts";
+import { getThemeByName, theme } from "../modes/interactive/theme/theme.ts";
 import { stripFrontmatter } from "../utils/frontmatter.ts";
 import { resolvePath } from "../utils/paths.ts";
 import { sleep } from "../utils/sleep.ts";
@@ -3017,7 +3017,8 @@ export class AgentSession {
 	 * @returns Path to exported file
 	 */
 	async exportToHtml(outputPath?: string): Promise<string> {
-		const themeName = this.settingsManager.getTheme();
+		const configuredThemeName = this.settingsManager.getTheme();
+		const themeName = configuredThemeName && getThemeByName(configuredThemeName) ? configuredThemeName : undefined;
 
 		// Create tool renderer if we have an extension runner (for custom tool HTML rendering)
 		const toolRenderer: ToolHtmlRenderer = createToolHtmlRenderer({

packages/coding-agent/test/suite/regressions/5596-missing-theme-export.test.ts

@@ -0,0 +1,89 @@
+import { existsSync, mkdtempSync, rmSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+import { Agent } from "@earendil-works/pi-agent-core";
+import { fauxAssistantMessage, registerFauxProvider } from "@earendil-works/pi-ai";
+import { afterEach, describe, expect, it } from "vitest";
+import { AgentSession } from "../../../src/core/agent-session.ts";
+import { AuthStorage } from "../../../src/core/auth-storage.ts";
+import { convertToLlm } from "../../../src/core/messages.ts";
+import { ModelRegistry } from "../../../src/core/model-registry.ts";
+import { SessionManager } from "../../../src/core/session-manager.ts";
+import { SettingsManager } from "../../../src/core/settings-manager.ts";
+import { initTheme } from "../../../src/modes/interactive/theme/theme.ts";
+import { createTestResourceLoader } from "../../utilities.ts";
+
+describe("regression #5596: missing configured theme export", () => {
+	const cleanups: Array<() => void> = [];
+
+	afterEach(() => {
+		while (cleanups.length > 0) {
+			cleanups.pop()?.();
+		}
+		initTheme("dark");
+	});
+
+	it("exports with the active fallback theme when the configured theme is missing", async () => {
+		const tempDir = mkdtempSync(join(tmpdir(), "pi-5596-"));
+		const faux = registerFauxProvider({
+			models: [{ id: "faux-1", reasoning: false }],
+		});
+		faux.setResponses([fauxAssistantMessage("hello")]);
+
+		const model = faux.getModel();
+		const authStorage = AuthStorage.inMemory();
+		authStorage.setRuntimeApiKey(model.provider, "faux-key");
+		const modelRegistry = ModelRegistry.inMemory(authStorage);
+		modelRegistry.registerProvider(model.provider, {
+			baseUrl: model.baseUrl,
+			apiKey: "faux-key",
+			api: faux.api,
+			models: faux.models.map((registeredModel) => ({
+				id: registeredModel.id,
+				name: registeredModel.name,
+				api: registeredModel.api,
+				reasoning: registeredModel.reasoning,
+				input: registeredModel.input,
+				cost: registeredModel.cost,
+				contextWindow: registeredModel.contextWindow,
+				maxTokens: registeredModel.maxTokens,
+				baseUrl: registeredModel.baseUrl,
+			})),
+		});
+
+		const settingsManager = SettingsManager.inMemory({ theme: "missing-theme" });
+		const sessionManager = SessionManager.create(tempDir, join(tempDir, "sessions"));
+		const agent = new Agent({
+			getApiKey: () => "faux-key",
+			initialState: {
+				model,
+				systemPrompt: "You are a test assistant.",
+				tools: [],
+			},
+			convertToLlm,
+		});
+		const session = new AgentSession({
+			agent,
+			sessionManager,
+			settingsManager,
+			cwd: tempDir,
+			modelRegistry,
+			resourceLoader: createTestResourceLoader(),
+		});
+		cleanups.push(() => {
+			session.dispose();
+			faux.unregister();
+			if (existsSync(tempDir)) {
+				rmSync(tempDir, { recursive: true, force: true });
+			}
+		});
+
+		await session.prompt("hi");
+		initTheme(settingsManager.getTheme());
+
+		const outputPath = join(tempDir, "export.html");
+		await expect(session.exportToHtml(outputPath)).resolves.toBe(outputPath);
+		expect(existsSync(outputPath)).toBe(true);
+		expect(settingsManager.getTheme()).toBe("missing-theme");
+	});
+});