stop showing opencode placeholder titles as if they were names

OpenCode titles a session from the conversation, but asynchronously — a finished turn of
ours ended up called "Single color in oc-red2.png", better than anything we would generate.
Until then the session is literally named "New session - 2026-08-10T15:44:17.178Z".

That window is exactly when a session is most visible: /chat/live shows turns that are
RUNNING, so the placeholder is what the panel catches, and a live row was being labelled
with a timestamp string.

Recognise it and treat it as untitled, so the good name arrives on its own. Passing --title
on the run was the other option and is worse: it fixes the transient case by permanently
replacing opencode own title with a truncated prompt, degrading it where it lasts longest.

A pattern match rather than startsWith, because a genuine title is allowed to begin with
those words. Two defects the tests caught while writing them: a whitespace-only title was
not treated as unnamed, and the mapping let undefined through where a string was required.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/servers/api/chat/opencode-sessions.test.ts

@@ -0,0 +1,27 @@
+import { describe, expect, it } from 'bun:test';
+import { isPlaceholderOpenCodeTitle } from './opencode-sessions';
+
+// OpenCode names a session `New session - <ISO>` until it has titled it from the conversation, which it
+// does asynchronously. The strings below are real ones observed on 1.18.16 — both the placeholder and
+// the good title it was replaced by.
+
+describe('isPlaceholderOpenCodeTitle', () => {
+  it('recognises the placeholder OpenCode uses before it has titled a session', () => {
+    expect(isPlaceholderOpenCodeTitle('New session - 2026-08-10T15:44:17.178Z')).toBe(true);
+    expect(isPlaceholderOpenCodeTitle('New session - 2026-08-10T12:41:02.757Z')).toBe(true);
+  });
+
+  it('treats an absent or empty title as unnamed too', () => {
+    expect(isPlaceholderOpenCodeTitle(undefined)).toBe(true);
+    expect(isPlaceholderOpenCodeTitle('')).toBe(true);
+    expect(isPlaceholderOpenCodeTitle('   ')).toBe(true);
+  });
+
+  it('keeps a real title, including one that merely mentions a session', () => {
+    // The title OpenCode actually gave a turn of ours, and the reason this is a pattern match rather
+    // than a `startsWith('New session')`: a genuine title is allowed to begin with those words.
+    expect(isPlaceholderOpenCodeTitle('Single color in oc-red2.png')).toBe(false);
+    expect(isPlaceholderOpenCodeTitle('New session handling in the runner')).toBe(false);
+    expect(isPlaceholderOpenCodeTitle('New session - what should it be called?')).toBe(false);
+  });
+});