fix(bridge): rawRPC direct polling + SDK analysis docs + trial-and-error log

- Root cause: getDiagnostics.lastStepIndex is stale, SDK EventMonitor cannot detect real-time step changes
- Fix: Direct rawRPC('GetCascadeTrajectorySteps') polling every 5s
- Relay: PLANNER_RESPONSE, NOTIFY_USER, TASK_BOUNDARY, WAITING steps
- Added: docs/discord-bridge-analysis.md (full SDK architecture analysis)
- Added: docs/devlog/entries/20260308-003.md (trial-and-error history)
- Added: antigravity-sdk-main/ source reference
- Vikunja: #252 done, #253 created, #251 commented

antigravity-sdk-main/src/core/disposable.ts

@@ -0,0 +1,73 @@
+/**
+ * Disposable pattern for resource cleanup.
+ *
+ * @module disposable
+ */
+
+/**
+ * An object that can release resources when no longer needed.
+ */
+export interface IDisposable {
+    dispose(): void;
+}
+
+/**
+ * Collects multiple disposables and disposes them all at once.
+ *
+ * @example
+ * ```typescript
+ * const store = new DisposableStore();
+ * store.add(someEventSub);
+ * store.add(anotherSub);
+ * // Later:
+ * store.dispose(); // cleans up everything
+ * ```
+ */
+export class DisposableStore implements IDisposable {
+    private readonly _disposables: IDisposable[] = [];
+    private _disposed = false;
+
+    /**
+     * Add a disposable to the store.
+     *
+     * @param disposable - The disposable to track
+     * @returns The same disposable (for chaining)
+     */
+    add<T extends IDisposable>(disposable: T): T {
+        if (this._disposed) {
+            disposable.dispose();
+            console.warn('[AntigravitySDK] Adding disposable to already disposed store');
+        } else {
+            this._disposables.push(disposable);
+        }
+        return disposable;
+    }
+
+    /**
+     * Dispose all tracked disposables.
+     */
+    dispose(): void {
+        if (this._disposed) {
+            return;
+        }
+        this._disposed = true;
+
+        for (const d of this._disposables) {
+            try {
+                d.dispose();
+            } catch (error) {
+                console.error('[AntigravitySDK] Dispose error:', error);
+            }
+        }
+        this._disposables.length = 0;
+    }
+}
+
+/**
+ * Creates a disposable from a cleanup function.
+ *
+ * @param fn - Cleanup function to call on dispose
+ */
+export function toDisposable(fn: () => void): IDisposable {
+    return { dispose: fn };
+}