feat(coding-agent): add JSONL export/import for sessions (#2356)

fixes #2274

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

@@ -13,8 +13,8 @@
  * Modes use this class and add their own I/O layer on top.
  */
 
-import { readFileSync } from "node:fs";
-import { basename, dirname, join } from "node:path";
+import { copyFileSync, existsSync, mkdirSync, readFileSync, writeFileSync } from "node:fs";
+import { basename, dirname, join, resolve } from "node:path";
 import type {
 	Agent,
 	AgentEvent,
@@ -73,7 +73,7 @@ import type { ModelRegistry } from "./model-registry.js";
 import { expandPromptTemplate, type PromptTemplate } from "./prompt-templates.js";
 import type { ResourceExtensionPaths, ResourceLoader } from "./resource-loader.js";
 import type { BranchSummaryEntry, CompactionEntry, SessionManager } from "./session-manager.js";
-import { getLatestCompactionEntry } from "./session-manager.js";
+import { CURRENT_SESSION_VERSION, getLatestCompactionEntry, type SessionHeader } from "./session-manager.js";
 import type { SettingsManager } from "./settings-manager.js";
 import { BUILTIN_SLASH_COMMANDS, type SlashCommandInfo, type SlashCommandLocation } from "./slash-commands.js";
 import { buildSystemPrompt } from "./system-prompt.js";
@@ -3067,6 +3067,68 @@ export class AgentSession {
 		});
 	}
 
+	/**
+	 * Export the current session branch to a JSONL file.
+	 * Writes the session header followed by all entries on the current branch path.
+	 * @param outputPath Target file path. If omitted, generates a timestamped file in cwd.
+	 * @returns The resolved output file path.
+	 */
+	exportToJsonl(outputPath?: string): string {
+		const filePath = resolve(outputPath ?? `session-${new Date().toISOString().replace(/[:.]/g, "-")}.jsonl`);
+		const dir = dirname(filePath);
+		if (!existsSync(dir)) {
+			mkdirSync(dir, { recursive: true });
+		}
+
+		const header: SessionHeader = {
+			type: "session",
+			version: CURRENT_SESSION_VERSION,
+			id: this.sessionManager.getSessionId(),
+			timestamp: new Date().toISOString(),
+			cwd: this.sessionManager.getCwd(),
+		};
+
+		const branchEntries = this.sessionManager.getBranch();
+		const lines = [JSON.stringify(header)];
+
+		// Re-chain parentIds to form a linear sequence
+		let prevId: string | null = null;
+		for (const entry of branchEntries) {
+			const linear = { ...entry, parentId: prevId };
+			lines.push(JSON.stringify(linear));
+			prevId = entry.id;
+		}
+
+		writeFileSync(filePath, `${lines.join("\n")}\n`);
+		return filePath;
+	}
+
+	/**
+	 * Import a JSONL session file.
+	 * Copies the file into the session directory and switches to it (like /resume).
+	 * @param inputPath Path to the JSONL file to import.
+	 * @returns true if the session was switched successfully.
+	 */
+	async importFromJsonl(inputPath: string): Promise<boolean> {
+		const resolved = resolve(inputPath);
+		if (!existsSync(resolved)) {
+			throw new Error(`File not found: ${resolved}`);
+		}
+
+		// Copy into the session directory so we don't modify the original
+		const sessionDir = this.sessionManager.getSessionDir();
+		if (!existsSync(sessionDir)) {
+			mkdirSync(sessionDir, { recursive: true });
+		}
+		const destPath = join(sessionDir, basename(resolved));
+		// Avoid overwriting if source and destination are the same file
+		if (resolve(destPath) !== resolved) {
+			copyFileSync(resolved, destPath);
+		}
+
+		return this.switchSession(destPath);
+	}
+
 	// =========================================================================
 	// Utilities
 	// =========================================================================

packages/coding-agent/src/core/slash-commands.ts

@@ -19,7 +19,8 @@ export const BUILTIN_SLASH_COMMANDS: ReadonlyArray<BuiltinSlashCommand> = [
 	{ name: "settings", description: "Open settings menu" },
 	{ name: "model", description: "Select model (opens selector UI)" },
 	{ name: "scoped-models", description: "Enable/disable models for Ctrl+P cycling" },
-	{ name: "export", description: "Export session to HTML file" },
+	{ name: "export", description: "Export session (HTML default, or specify path: .html/.jsonl)" },
+	{ name: "import", description: "Import and resume a session from a JSONL file" },
 	{ name: "share", description: "Share session as a secret GitHub gist" },
 	{ name: "copy", description: "Copy last agent message to clipboard" },
 	{ name: "name", description: "Set session display name" },

packages/coding-agent/src/modes/interactive/interactive-mode.ts

@@ -1977,6 +1977,11 @@ export class InteractiveMode {
 				this.editor.setText("");
 				return;
 			}
+			if (text.startsWith("/import")) {
+				await this.handleImportCommand(text);
+				this.editor.setText("");
+				return;
+			}
 			if (text === "/share") {
 				await this.handleShareCommand();
 				this.editor.setText("");
@@ -3909,13 +3914,62 @@ export class InteractiveMode {
 		const outputPath = parts.length > 1 ? parts[1] : undefined;
 
 		try {
-			const filePath = await this.session.exportToHtml(outputPath);
-			this.showStatus(`Session exported to: ${filePath}`);
+			if (outputPath?.endsWith(".jsonl")) {
+				const filePath = this.session.exportToJsonl(outputPath);
+				this.showStatus(`Session exported to: ${filePath}`);
+			} else {
+				const filePath = await this.session.exportToHtml(outputPath);
+				this.showStatus(`Session exported to: ${filePath}`);
+			}
 		} catch (error: unknown) {
 			this.showError(`Failed to export session: ${error instanceof Error ? error.message : "Unknown error"}`);
 		}
 	}
 
+	private async handleImportCommand(text: string): Promise<void> {
+		const parts = text.split(/\s+/);
+		if (parts.length < 2 || !parts[1]) {
+			this.showError("Usage: /import <path.jsonl>");
+			return;
+		}
+		const inputPath = parts[1];
+
+		const confirmed = await this.showExtensionConfirm("Import session", `Replace current session with ${inputPath}?`);
+		if (!confirmed) {
+			this.showStatus("Import cancelled");
+			return;
+		}
+
+		try {
+			// Stop loading animation
+			if (this.loadingAnimation) {
+				this.loadingAnimation.stop();
+				this.loadingAnimation = undefined;
+			}
+			this.statusContainer.clear();
+
+			// Clear UI state
+			this.pendingMessagesContainer.clear();
+			this.compactionQueuedMessages = [];
+			this.streamingComponent = undefined;
+			this.streamingMessage = undefined;
+			this.pendingTools.clear();
+
+			const success = await this.session.importFromJsonl(inputPath);
+			if (!success) {
+				this.showWarning("Import cancelled");
+				return;
+			}
+
+			// Clear and re-render the chat
+			this.chatContainer.clear();
+			this.renderInitialMessages();
+			this.showStatus(`Session imported from: ${inputPath}`);
+		} catch (error: unknown) {
+			this.showError(`Failed to import session: ${error instanceof Error ? error.message : "Unknown error"}`);
+		}
+	}
+
 	private async handleShareCommand(): Promise<void> {
 		// Check if gh is available and logged in
 		try {