fix(fork): truncate the slim composer placeholder under the pills

.fork/customizations.yaml

@@ -674,11 +674,14 @@
     absolutely positioned overlay outside the editor's scroll box — wraps and
     paints straight through the 48px box, and stably so (the overlay never
     changes the observed editor height, so the latch cannot rescue it). A
-    narrow viewport resolves tall regardless. States the designs do not draw
-    also resolve tall: an approval request, a pending user-input question, and
-    the plan follow-up banner all own the box's internals and carry their own
-    action rows. Attachments deliberately do not force tall — attachment cards
-    render as a full-width band above the inline row.
+    narrow viewport resolves tall regardless. On desktop slim the same overlay
+    still outruns a short editor column: the placeholder truncates with an
+    ellipsis (nowrap on the Lexical sibling, overflow-hidden on the prompt
+    column) rather than wrapping under the inline pills. States the designs do
+    not draw also resolve tall: an approval request, a pending user-input
+    question, and the plan follow-up banner all own the box's internals and
+    carry their own action rows. Attachments deliberately do not force tall —
+    attachment cards render as a full-width band above the inline row.
     The control row renders in every density, including collapsed; only its
     left half is conditional. The run controls are gated on a pending approval
     — they moved out of the box, which upstream unmounted wholesale during

apps/web/src/__fork_guards__/forkComposerShell.test.ts

@@ -303,6 +303,19 @@ describe("fork guard: fork-composer-shell", () => {
     ).toBe("tall");
   });
 
+  it("truncates the slim-shell placeholder instead of letting it wrap under the pills", () => {
+    // Same absolute-overlay failure mode as the phone case, just on a desktop
+    // slim row whose editor column is still narrower than the long empty-state
+    // hint. Truncate on one line; do not apply nowrap to the editor itself.
+    expect(theme).toMatch(
+      /\[data-fork-composer-density="slim"\][\s\S]{0,200}\[data-testid="composer-editor"\]\s*~\s*div[\s\S]{0,160}text-overflow:\s*ellipsis/u,
+    );
+    expect(theme).toMatch(
+      /\[data-fork-composer-density="slim"\][\s\S]{0,200}\[data-testid="composer-editor"\]\s*~\s*div[\s\S]{0,160}white-space:\s*nowrap/u,
+    );
+    expect(chatComposer).toMatch(/isComposerSlim && "overflow-hidden"/u);
+  });
+
   it("keeps the branch controls reachable while collapsed, and gates modes on approval", () => {
     // Two upstream behaviours the control row has to preserve. Upstream showed
     // BranchToolbar while collapsed (gated on showComposerContextStrip alone),

apps/web/src/components/chat/ChatComposer.tsx

@@ -2732,7 +2732,13 @@ export const ChatComposer = memo(function ChatComposer(props: ChatComposerProps)
 
             {/* fork:begin fork-composer-shell — see .fork/customizations.yaml#fork-composer-shell */}
             <div className={cn("flex min-w-0", isComposerSlim ? "items-center gap-6" : "flex-col")}>
-              <div ref={attachPromptElement} className="relative min-w-0 flex-1">
+              {/* overflow-hidden on slim: the absolute placeholder can still paint
+                  past the editor column into the inline pills if something misses
+                  the ellipsis rule; clip at the column edge. */}
+              <div
+                ref={attachPromptElement}
+                className={cn("relative min-w-0 flex-1", isComposerSlim && "overflow-hidden")}
+              >
                 {/* fork:end fork-composer-shell */}
                 <ComposerPromptEditor
                   editorRef={composerEditorRef}

apps/web/src/theme.custom.css

@@ -381,6 +381,21 @@
   }
 }
 
+/* Slim shell: the empty-state hint is an absolute overlay outside the editor's
+   scroll box. Wrapping never grows the observed editor height, so the wrap latch
+   cannot flip the shell to tall — and the second line paints straight through the
+   inline model pill and send button. Truncate on one line instead. The spacer
+   sibling is empty, so nowrap is a no-op there. Tall keeps wrapping: the prompt
+   owns the full width and the box has room. */
+:root[data-fork="noahhendrickson-t3code"]
+  [data-fork-composer-density="slim"]
+  [data-testid="composer-editor"]
+  ~ div {
+  overflow: hidden;
+  text-overflow: ellipsis;
+  white-space: nowrap;
+}
+
 /* The in-box pills and the control row below it share one 24px ghost treatment:
    12px medium type, a 12px glyph, and a full pill. The designs draw this type at
    10px; 12px is the fork's own call, and it matches the prompt beside it.