feat(plugins): add export-format registration hook to plugin API

Add context.formats.registerExportFormat(id, opts) to PluginContext,
backed by a new FormatRegistry (mirrors PluginRegistry's Map-based
shape). Plugins register namespaced (${pluginId}:${id}) export
formats with a label/extension/handler; the writing-studio built-in
plugin registers a trivial "sprint-summary" .txt export as a
worked example.

The plugin system lives entirely in the renderer process while the
Export menu is built in main.js, so wiring formats into the menu
required a small IPC round-trip: renderer sends format metadata to
main after plugin load (main rebuilds the menu via the already-
idempotent createMenu()), and a menu click sends the resolved save
path back to the renderer, which is the only process holding the
plugin's handler function.

Amit Haridas

src/plugins/built-in/writing-studio/index.js

@@ -29,6 +29,7 @@ class WritingStudioPlugin extends PluginAPI {
 
     this._registerCommands(context);
     this._registerStatusBar(context);
+    this._registerExportFormats(context);
   }
 
   _registerCommands(context) {
@@ -120,6 +121,42 @@ class WritingStudioPlugin extends PluginAPI {
     });
   }
 
+  // Example usage of context.formats.registerExportFormat (Task 17): adds
+  // a "Writing Studio Summary" entry to the Export menu that writes a
+  // plain-text snapshot of today's sprint/goal progress instead of going
+  // through Pandoc. Doubles as documentation for how a plugin can offer
+  // its own export target.
+  _registerExportFormats(context) {
+    const { sprintEngine, goalTracker } = this;
+
+    context.formats.registerExportFormat('sprint-summary', {
+      label: 'Writing Studio Summary (.txt)',
+      extension: 'txt',
+      handler: async (markdownContent, outputPath) => {
+        const fs = require('fs');
+        const goal = context.settings.get('dailyGoal') || 1000;
+        const progress = goalTracker.getDailyProgress(goal);
+        const streak = goalTracker.getStreak(goal);
+        const wordCount = (markdownContent || '').split(/\s+/).filter(Boolean).length;
+
+        const lines = [
+          'Writing Studio Summary',
+          '=======================',
+          `Generated: ${new Date().toISOString()}`,
+          '',
+          `Document word count: ${wordCount}`,
+          `Daily goal: ${goal}`,
+          `Words written today: ${progress.written} (${progress.pct}%)`,
+          `Current streak: ${streak} day(s)`,
+          `Sprint active: ${sprintEngine.isActive() ? 'yes' : 'no'}`,
+          '',
+        ];
+
+        fs.writeFileSync(outputPath, lines.join('\n'), 'utf-8');
+      },
+    });
+  }
+
   deactivate() {
     if (this._sprintInterval) clearInterval(this._sprintInterval);
   }

src/plugins/built-in/writing-studio/manifest.json

@@ -32,7 +32,14 @@
         "shortcut": "Ctrl+Alt+G"
       }
     ],
-    "statusBar": { "indicators": ["sprint-timer", "word-goal"] }
+    "statusBar": { "indicators": ["sprint-timer", "word-goal"] },
+    "exportFormats": [
+      {
+        "id": "sprint-summary",
+        "label": "Writing Studio Summary (.txt)",
+        "extension": "txt"
+      }
+    ]
   },
   "settings": [
     { "key": "dailyGoal", "type": "number", "default": 1000, "label": "Daily word goal" },

src/plugins/format-registry.js

@@ -0,0 +1,40 @@
+/**
+ * FormatRegistry — tracks export formats registered by plugins via
+ * `context.formats.registerExportFormat(id, opts)`.
+ *
+ * Mirrors the simple Map-backed storage pattern used by PluginRegistry
+ * (see plugin-registry.js), scoped to a single concern: export format
+ * metadata + handler functions rather than whole plugin instances.
+ */
+class FormatRegistry {
+  constructor() {
+    this.formats = new Map();
+  }
+
+  /**
+   * Register (or overwrite) an export format entry.
+   * @param {string} id - Fully-namespaced format id, e.g. "writing-studio:sprint-summary"
+   * @param {object} opts - { label, extension, handler: async (markdownContent, outputPath, options) => void }
+   */
+  register(id, opts) {
+    this.formats.set(id, opts);
+  }
+
+  /**
+   * Look up a single registered format entry by its namespaced id.
+   * @param {string} id
+   * @returns {object|undefined}
+   */
+  get(id) {
+    return this.formats.get(id);
+  }
+
+  /**
+   * Return all registered formats as an array of { id, ...opts }.
+   */
+  getAll() {
+    return Array.from(this.formats.entries()).map(([id, opts]) => ({ id, ...opts }));
+  }
+}
+
+module.exports = { FormatRegistry };

src/plugins/plugin-context.js

@@ -10,10 +10,21 @@ class PluginContext {
    * @param {object} deps.editor - { getContent, getSelection, insertAtCursor, onContentChanged }
    * @param {object} deps.ipc - { invoke, on }
    * @param {object} deps.exportHooks - { preHooks: [], postHooks: [] }
+   * @param {object} deps.formatRegistry - FormatRegistry instance ({ register, get, getAll })
    */
   constructor(deps) {
-    const { pluginId, sidebar, commands, statusBar, eventBus, settings, editor, ipc, exportHooks } =
-      deps;
+    const {
+      pluginId,
+      sidebar,
+      commands,
+      statusBar,
+      eventBus,
+      settings,
+      editor,
+      ipc,
+      exportHooks,
+      formatRegistry,
+    } = deps;
 
     this.sidebar = {
       registerPanel: (id, opts) => sidebar.registerPanel(`${pluginId}:${id}`, opts),
@@ -69,6 +80,19 @@ class PluginContext {
         if (exportHooks) exportHooks.postHooks.push(handler);
       },
     };
+
+    this.formats = {
+      /**
+       * Register a plugin-provided export format. It is namespaced as
+       * `${pluginId}:${id}` so plugins can't collide with each other or
+       * with the built-in Pandoc-backed formats.
+       * @param {string} id - Format id, unique within this plugin.
+       * @param {object} opts - { label, extension, handler: async (markdownContent, outputPath, options) => void }
+       */
+      registerExportFormat: (id, opts) => {
+        if (formatRegistry) formatRegistry.register(`${pluginId}:${id}`, opts);
+      },
+    };
   }
 }
 

src/plugins/plugin-registry.js

@@ -33,6 +33,7 @@ class PluginRegistry {
       editor: this.deps.editor,
       ipc: this.deps.ipc,
       exportHooks: this.exportHooks,
+      formatRegistry: this.deps.formatRegistry,
     });
 
     try {