fix(cookbook): recover completed downloads from DOWNLOAD_OK in background reconciler (#4000)

The dashboard background status reconciler (_pollBackgroundStatus) only
recovered "done" for dependency installs when the backend reported a
finished task as "stopped". A real model download whose tmux pane is
gone after DOWNLOAD_OK (so the dead-session check misses the landed
snapshot) fell through to `task.type === 'download' ? 'crashed'`, so a
completed download was shown as crashed (and stalled on the Serve tab).

Recover "done" from the terminal DOWNLOAD_OK sentinel, mirroring the
dep-install recovery already present. The background poll runs blind, so
it keys off the conclusive exit-0 sentinel only — not the `/snapshots/`
path, which can be printed mid-stream for multi-file downloads and would
risk marking an incomplete download done.

Fixes #3897

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

static/js/cookbookRunning.js

@@ -3533,12 +3533,22 @@ async function _pollBackgroundStatus() {
         // dead-session check inspects). Recover "done" from the retained output's
         // exit-0 sentinel so a clean install isn't downgraded to crashed.
         const depDone = !!task.payload?._dep && _depInstallSucceeded(task.output);
+        // A finished model download whose tmux pane is gone is also reported
+        // "stopped" (the dead-session check can miss the landed snapshot).
+        // Recover "done" from the terminal `DOWNLOAD_OK` sentinel — emitted
+        // only after the runner exits 0 — so a completed download isn't
+        // downgraded to crashed. This background poll runs blind (no live
+        // stream to debounce against), so unlike the reconnect loop it keys
+        // off the conclusive exit sentinel only, never the `/snapshots/` path,
+        // which can be printed mid-stream for multi-file downloads.
+        const downloadDone = task.type === 'download'
+          && String(task.output || '').includes('DOWNLOAD_OK');
         const nextStatus = live.status === 'completed'
           ? 'done'
           : (live.status === 'error'
             ? 'error'
             : (live.status === 'stopped'
-                ? (depDone ? 'done' : (task.type === 'download' ? 'crashed' : 'stopped'))
+                ? ((depDone || downloadDone) ? 'done' : (task.type === 'download' ? 'crashed' : 'stopped'))
                 : null));
         if (nextStatus && task.status !== nextStatus) {
           updates.status = nextStatus;

tests/test_cookbook_dependency_completion_regression.py

@@ -74,7 +74,23 @@ def test_background_poll_recovers_done_for_stopped_dependency_install():
     source = _read("static/js/cookbookRunning.js")
 
     assert "const depDone = !!task.payload?._dep && _depInstallSucceeded(task.output);" in source
-    assert "depDone ? 'done' : (task.type === 'download' ? 'crashed' : 'stopped')" in source
+    assert "(depDone || downloadDone) ? 'done' : (task.type === 'download' ? 'crashed' : 'stopped')" in source
+
+
+def test_background_poll_recovers_done_for_completed_download():
+    """When the backend reports a finished model download as "stopped" (its
+    tmux pane is gone after DOWNLOAD_OK, so the dead-session check can miss the
+    landed snapshot), the reconciler must recover "done" from the terminal
+    DOWNLOAD_OK sentinel instead of downgrading the card to crashed. The
+    background poll keys off DOWNLOAD_OK only (not the "/snapshots/" path, which
+    can appear mid-stream for multi-file downloads)."""
+    source = _read("static/js/cookbookRunning.js")
+
+    normalized = " ".join(source.split())
+    assert (
+        "const downloadDone = task.type === 'download' "
+        "&& String(task.output || '').includes('DOWNLOAD_OK');"
+    ) in normalized
 
 
 def test_dependency_install_payload_keeps_env_path_for_refresh():