Merge branch 'feature/cancel-queued-message' into predev

# Conflicts:
#	backend-handoff.md

2 files changed, 119 insertions, 1 deletions

diff --git a/src/features/surface-host/logic/message-queue.test.ts b/src/features/surface-host/logic/message-queue.test.ts
index 8d55eb7..ae91c8f 100644
--- a/src/features/surface-host/logic/message-queue.test.ts
+++ b/src/features/surface-host/logic/message-queue.test.ts
@@ -1,6 +1,10 @@
 import type { QueuedMessage } from "@dispatch/wire";
 import { describe, expect, it } from "vitest";
-import { parseMessageQueuePayload } from "./message-queue";
+import {
+  parseMessageQueuePayload,
+  reconcileCancelledIds,
+  selectVisibleMessages,
+} from "./message-queue";
 
 const msg = (id: string, text: string, queuedAt = 1_700_000_000_000): QueuedMessage => ({
   id,
@@ -46,3 +50,56 @@ describe("parseMessageQueuePayload", () => {
     expect(parseMessageQueuePayload(payload)).toBeNull();
   });
 });
+
+describe("selectVisibleMessages", () => {
+  it("returns the snapshot unchanged when nothing is cancelled", () => {
+    const messages = [msg("m1", "a"), msg("m2", "b")];
+    expect(selectVisibleMessages(messages, new Set())).toBe(messages);
+  });
+
+  it("hides the optimistically-cancelled row", () => {
+    const messages = [msg("m1", "a"), msg("m2", "b"), msg("m3", "c")];
+    expect(selectVisibleMessages(messages, new Set(["m2"])).map((m) => m.id)).toEqual(["m1", "m3"]);
+  });
+
+  it("hides multiple cancelled rows", () => {
+    const messages = [msg("m1", "a"), msg("m2", "b"), msg("m3", "c")];
+    expect(selectVisibleMessages(messages, new Set(["m1", "m3"])).map((m) => m.id)).toEqual(["m2"]);
+  });
+
+  it("tolerates a cancelled id not present in the snapshot (no-op)", () => {
+    const messages = [msg("m1", "a")];
+    expect(selectVisibleMessages(messages, new Set(["ghost"])).map((m) => m.id)).toEqual(["m1"]);
+  });
+});
+
+describe("reconcileCancelledIds", () => {
+  it("returns an empty set when nothing was cancelled", () => {
+    const result = reconcileCancelledIds([msg("m1", "a")], new Set());
+    expect(result.size).toBe(0);
+  });
+
+  it("drops ids the surface confirmed gone (no longer queued)", () => {
+    // m1 still queued (cancel pending), m2 confirmed gone (left the snapshot).
+    const messages = [msg("m1", "a")];
+    const result = reconcileCancelledIds(messages, new Set(["m1", "m2"]));
+    expect([...result]).toEqual(["m1"]);
+  });
+
+  it("returns the SAME set identity when nothing changed (no spurious cycle)", () => {
+    const messages = [msg("m1", "a"), msg("m2", "b")];
+    const cancelled = new Set(["m1", "m2"]);
+    expect(reconcileCancelledIds(messages, cancelled)).toBe(cancelled);
+  });
+
+  it("returns an empty set when all cancels were confirmed", () => {
+    const messages = [msg("m1", "a")];
+    expect(reconcileCancelledIds(messages, new Set(["m2", "m3"])).size).toBe(0);
+  });
+
+  it("keeps a still-queued cancelled id (cancel still pending)", () => {
+    const messages = [msg("m1", "a"), msg("m2", "b")];
+    const result = reconcileCancelledIds(messages, new Set(["m2"]));
+    expect([...result]).toEqual(["m2"]);
+  });
+});
diff --git a/src/features/surface-host/logic/message-queue.ts b/src/features/surface-host/logic/message-queue.ts
index 79707a5..7a3653e 100644
--- a/src/features/surface-host/logic/message-queue.ts
+++ b/src/features/surface-host/logic/message-queue.ts
@@ -43,3 +43,64 @@ export function parseMessageQueuePayload(payload: unknown): MessageQueueData | n
 
 /** The `rendererId` the message-queue extension's `custom` surface field uses. */
 export const MESSAGE_QUEUE_RENDERER_ID = "message-queue";
+
+/**
+ * Optimistic-removal view-model for the queue list.
+ *
+ * The `chat.queue.cancel` op is fire-and-forget + idempotent: success is
+ * confirmed by the `message-queue` SURFACE updating (the cancelled message
+ * leaves the snapshot), not by a reply. To avoid a flash of the row lingering
+ * for a round-trip, the renderer hides a row the instant the user clicks cancel
+ * (tracking the cancelled id locally), then reconciles when the surface pushes
+ * the post-cancel snapshot. These two pure helpers drive that — the component
+ * holds the cancelled-id set as a thin `$state` wrapper and delegates all
+ * decisions here.
+ */
+
+/**
+ * The messages the renderer should show: the surface snapshot MINUS any
+ * optimistically-cancelled ids (a cancel whose surface confirmation hasn't
+ * arrived yet). Pure — no mutation of inputs.
+ */
+export function selectVisibleMessages(
+  messages: readonly QueuedMessage[],
+  cancelledIds: ReadonlySet<string>,
+): readonly QueuedMessage[] {
+  if (cancelledIds.size === 0) return messages;
+  return messages.filter((m) => !cancelledIds.has(m.id));
+}
+
+/**
+ * Reconcile the cancelled-id set against a NEW surface snapshot: keep only the
+ * ids that are STILL queued (the cancel is pending — its surface confirmation
+ * hasn't landed). Drop ids that have left the snapshot: the server confirmed
+ * the removal (or the message drained as steering / the queue cleared), so the
+ * optimistic hide is no longer needed. This keeps the set bounded — it never
+ * outlives the rows it tracks. Pure — returns a NEW set (callers assign it to
+ * the reactive `$state`).
+ */
+export function reconcileCancelledIds(
+  messages: readonly QueuedMessage[],
+  cancelledIds: ReadonlySet<string>,
+): ReadonlySet<string> {
+  if (cancelledIds.size === 0) return EMPTY_STRING_SET;
+  const stillQueued = new Set<string>();
+  for (const m of messages) {
+    if (cancelledIds.has(m.id)) stillQueued.add(m.id);
+  }
+  // Same set back → return the input identity so the component's `$state` setter
+  // sees no change (avoids a spurious reactive cycle).
+  if (stillQueued.size === cancelledIds.size) {
+    let same = true;
+    for (const id of cancelledIds) {
+      if (!stillQueued.has(id)) {
+        same = false;
+        break;
+      }
+    }
+    if (same) return cancelledIds;
+  }
+  return stillQueued;
+}
+
+const EMPTY_STRING_SET: ReadonlySet<string> = new Set<string>();