fix: tone down branch-mismatch banner

apps/web/src/components/ChatView.logic.test.ts

@@ -12,16 +12,20 @@ import type { Thread } from "../types";
 import {
   MAX_HIDDEN_MOUNTED_PREVIEW_THREADS,
   MAX_HIDDEN_MOUNTED_TERMINAL_THREADS,
+  branchMismatchKey,
   buildExpiredTerminalContextToastCopy,
   buildThreadTurnInterruptInput,
   createLocalDispatchSnapshot,
   deriveComposerSendState,
+  dismissBranchMismatchForSession,
   getStartedThreadModelChangeBlockReason,
   hasServerAcknowledgedLocalDispatch,
+  isBranchMismatchDismissedForSession,
   reconcileMountedTerminalThreadIds,
   reconcileRetainedMountedThreadIds,
   resolveThreadMetadataUpdateForNextTurn,
   resolveSendEnvMode,
+  shouldShowBranchMismatchBanner,
   shouldWriteThreadErrorToCurrentServerThread,
 } from "./ChatView.logic";
 
@@ -292,6 +296,61 @@ describe("resolveSendEnvMode", () => {
   });
 });
 
+describe("branchMismatchKey", () => {
+  it("builds a key from thread id and both branches", () => {
+    expect(branchMismatchKey("thread-1", { threadBranch: "feat/a", currentBranch: "feat/b" })).toBe(
+      "thread-1:feat/a:feat/b",
+    );
+  });
+
+  it("returns null without a thread or mismatch", () => {
+    expect(branchMismatchKey(null, { threadBranch: "a", currentBranch: "b" })).toBeNull();
+    expect(branchMismatchKey("thread-1", null)).toBeNull();
+  });
+});
+
+describe("shouldShowBranchMismatchBanner", () => {
+  const base = {
+    hasMismatch: true,
+    isDismissed: false,
+    composerHasContent: false,
+    wasShownForCurrentMismatch: false,
+  };
+
+  it("stays hidden during passive browsing (even though the composer autofocuses)", () => {
+    expect(shouldShowBranchMismatchBanner(base)).toBe(false);
+  });
+
+  it("shows once the composer has draft content", () => {
+    expect(shouldShowBranchMismatchBanner({ ...base, composerHasContent: true })).toBe(true);
+  });
+
+  it("stays mounted after the draft clears once shown for the current mismatch", () => {
+    expect(shouldShowBranchMismatchBanner({ ...base, wasShownForCurrentMismatch: true })).toBe(
+      true,
+    );
+  });
+
+  it("never shows when dismissed or without a mismatch", () => {
+    expect(
+      shouldShowBranchMismatchBanner({ ...base, composerHasContent: true, isDismissed: true }),
+    ).toBe(false);
+    expect(
+      shouldShowBranchMismatchBanner({ ...base, composerHasContent: true, hasMismatch: false }),
+    ).toBe(false);
+  });
+});
+
+describe("session branch mismatch dismissal", () => {
+  it("tracks dismissed keys and treats other keys as active", () => {
+    expect(isBranchMismatchDismissedForSession("t1:a:b")).toBe(false);
+    dismissBranchMismatchForSession("t1:a:b");
+    expect(isBranchMismatchDismissedForSession("t1:a:b")).toBe(true);
+    expect(isBranchMismatchDismissedForSession("t1:a:c")).toBe(false);
+    expect(isBranchMismatchDismissedForSession(null)).toBe(false);
+  });
+});
+
 describe("reconcileMountedTerminalThreadIds", () => {
   it("keeps open threads and makes the active thread most recent", () => {
     expect(

apps/web/src/components/ChatView.logic.ts

@@ -289,6 +289,46 @@ export function buildExpiredTerminalContextToastCopy(
   };
 }
 
+export function branchMismatchKey(
+  threadId: string | null,
+  mismatch: { threadBranch: string; currentBranch: string } | null,
+): string | null {
+  if (!threadId || !mismatch) {
+    return null;
+  }
+  return `${threadId}:${mismatch.threadBranch}:${mismatch.currentBranch}`;
+}
+
+// The mismatch banner only matters when the user is about to send: passive
+// reading of an old thread carries no risk (the branch picker tint already
+// covers ambient awareness). Draft content is the intent signal — composer
+// focus is useless here because ChatView autofocuses the composer on every
+// thread open. `wasShownForCurrentMismatch` keeps the banner mounted once
+// revealed so it doesn't flicker away when the draft is cleared.
+export function shouldShowBranchMismatchBanner(input: {
+  hasMismatch: boolean;
+  isDismissed: boolean;
+  composerHasContent: boolean;
+  wasShownForCurrentMismatch: boolean;
+}): boolean {
+  if (!input.hasMismatch || input.isDismissed) {
+    return false;
+  }
+  return input.composerHasContent || input.wasShownForCurrentMismatch;
+}
+
+// Session-scoped (module-level so it survives ChatView remounts, e.g. route
+// changes). Durable cross-device dismissal is planned as a server-side ack.
+const sessionDismissedBranchMismatchKeys = new Set<string>();
+
+export function dismissBranchMismatchForSession(key: string): void {
+  sessionDismissedBranchMismatchKeys.add(key);
+}
+
+export function isBranchMismatchDismissedForSession(key: string | null): boolean {
+  return key !== null && sessionDismissedBranchMismatchKeys.has(key);
+}
+
 export function threadHasStarted(thread: Thread | null | undefined): boolean {
   return Boolean(
     thread && (thread.latestTurn !== null || thread.messages.length > 0 || thread.session !== null),