fix(discord): add media dedup production code for messaging tool pipeline

Wire media URL tracking through the embedded agent pipeline so that
media already sent via messaging tools is not delivered again by the
reply dispatcher.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/agents/pi-embedded-subscribe.handlers.tools.media.test-helpers.ts

@@ -0,0 +1,68 @@
+import type { AgentEvent } from "@mariozechner/pi-agent-core";
+import type { Mock } from "vitest";
+import type { EmbeddedPiSubscribeContext } from "./pi-embedded-subscribe.handlers.types.js";
+import type { SubscribeEmbeddedPiSessionParams } from "./pi-embedded-subscribe.types.js";
+import {
+  handleToolExecutionEnd,
+  handleToolExecutionStart,
+} from "./pi-embedded-subscribe.handlers.tools.js";
+
+/**
+ * Narrowed params type that omits the `session` class instance (never accessed
+ * by the handler paths under test).
+ */
+type TestParams = Omit<SubscribeEmbeddedPiSessionParams, "session">;
+
+/**
+ * The subset of {@link EmbeddedPiSubscribeContext} that the media-emission
+ * tests actually populate.  Using this avoids the need for `as unknown as`
+ * double-assertion in every mock factory.
+ */
+export type MockEmbeddedContext = Omit<EmbeddedPiSubscribeContext, "params"> & {
+  params: TestParams;
+};
+
+/** Type-safe bridge: narrows parameter type so callers avoid assertions. */
+function asFullContext(ctx: MockEmbeddedContext): EmbeddedPiSubscribeContext {
+  return ctx as unknown as EmbeddedPiSubscribeContext;
+}
+
+/** Typed wrapper around {@link handleToolExecutionStart}. */
+export function callToolExecutionStart(
+  ctx: MockEmbeddedContext,
+  evt: AgentEvent & { toolName: string; toolCallId: string; args: unknown },
+): Promise<void> {
+  return handleToolExecutionStart(asFullContext(ctx), evt);
+}
+
+/** Typed wrapper around {@link handleToolExecutionEnd}. */
+export function callToolExecutionEnd(
+  ctx: MockEmbeddedContext,
+  evt: AgentEvent & {
+    toolName: string;
+    toolCallId: string;
+    isError: boolean;
+    result?: unknown;
+  },
+): Promise<void> {
+  return handleToolExecutionEnd(asFullContext(ctx), evt);
+}
+
+/**
+ * Check whether a mock-call argument is an object containing `mediaUrls`
+ * but NOT `text` (i.e. a "direct media" emission).
+ */
+export function isDirectMediaCall(call: unknown[]): boolean {
+  const arg = call[0];
+  if (!arg || typeof arg !== "object") {
+    return false;
+  }
+  return "mediaUrls" in arg && !("text" in arg);
+}
+
+/**
+ * Filter a vi.fn() mock's call log to only direct-media emissions.
+ */
+export function filterDirectMediaCalls(mock: Mock): unknown[][] {
+  return mock.mock.calls.filter(isDirectMediaCall);
+}