Harden generate against tunnel drops and missing i2v anchors.

Retry save and queue requests on transient HTTP 530/502 errors, block generate
when the project failed to save, and return a clear error if anchor media is gone.

movie_editor/backend/timeline.py

@@ -360,8 +360,20 @@ def continuity_media_refs(full: Project, target: Project) -> list[str]:
     return list(dict.fromkeys(refs))
 
 
-@dataclass
-class GuideEntry:
+def scene_anchor_media_refs(target: Project) -> list[str]:
+    """Media-bin ids required as i2v anchors on generative scenes."""
+    refs: list[str] = []
+    for sc in target.scenes:
+        if sc.excluded or is_video_clip(sc):
+            continue
+        src = sc.source
+        if not src:
+            continue
+        stype = source_type(sc)
+        ref = src.media_ref
+        if ref and stype in ("image", "generated_frame", "mixed"):
+            refs.append(ref)
+    return list(dict.fromkeys(refs))
     """Optional per-scene guide (only used when project guide_settings.stack_enabled)."""
     enabled: bool = True
     source: str = "template"   # "template" | "scene" | "image"

movie_editor/frontend/store.js

@@ -730,7 +730,7 @@
       state.saving = true;
       _notifySaveChip();
       try {
-        const saved = await API.saveProject(snapshot.id, snapshot);
+        const saved = await _retryOnTunnel(() => API.saveProject(snapshot.id, snapshot));
         // If the user edited again while this save was in flight (e.g. dropped a new
         // anchor), do NOT replace local state with the older snapshot we just wrote.
         if (_localDirty) scheduleSave();
@@ -1690,6 +1690,31 @@
     return /HTTP 53[0-9]|HTTP 52[24]|HTTP 502|Failed to fetch|NetworkError|Load failed|fetch/i.test(m);
   }
 
+  async function _retryOnTunnel(fn, attempts) {
+    attempts = attempts || 8;
+    let last;
+    for (let i = 0; i < attempts; i++) {
+      try {
+        return await fn();
+      } catch (e) {
+        last = e;
+        if (!_isTransientTunnelError(e) || i >= attempts - 1) throw e;
+        await _sleep(1500 + i * 500);
+      }
+    }
+    throw last;
+  }
+
+  async function _flushSaveForGenerate() {
+    await flushSave();
+    if (_localDirty) {
+      throw new Error(
+        "Could not save your latest edits before generate (tunnel may have dropped). "
+        + "Wait for the save indicator to clear, then try again."
+      );
+    }
+  }
+
   function _sleep(ms) {
     return new Promise((resolve) => setTimeout(resolve, ms));
   }
@@ -2130,7 +2155,10 @@
     _markGenInFlight(sceneIds);
     set({ gen: { state: "queuing", promptId: null, media: [], msg: `${prefix}: queuing…`, step: 0, maxStep: 0 } });
     try {
-      const r = await API.generate(state.project.id, onlyScene || null, onlyScene ? null : sceneIds, !!resetSession);
+      const r = await _retryOnTunnel(
+        () => API.generate(state.project.id, onlyScene || null, onlyScene ? null : sceneIds, !!resetSession),
+        10,
+      );
       if (!r.prompt_id) { set({ gen: { ...state.gen, state: "error", msg: "No prompt id returned." } }); return false; }
       _queueRenderPrompts(sceneIds);
       if (r.validation && state.project) {
@@ -2161,7 +2189,12 @@
 
   async function generate(onlyScene) {
     if (!state.project) return;
-    await flushSave();
+    try {
+      await _flushSaveForGenerate();
+    } catch (e) {
+      set({ gen: { state: "error", promptId: null, media: [], msg: _friendlyGenError(e.message) } });
+      return;
+    }
     if (!onlyScene) return generateMontage();
     const reset = _resetSessionPending; _resetSessionPending = false;
     if (reset) state.resetSessionArmed = false;
@@ -2175,7 +2208,12 @@
   // session reset applies to the FIRST run only.
   async function generateMontage() {
     if (!state.project) return;
-    await flushSave();
+    try {
+      await _flushSaveForGenerate();
+    } catch (e) {
+      set({ gen: { state: "error", promptId: null, media: [], msg: _friendlyGenError(e.message) } });
+      return;
+    }
     const runs = _runs();
     if (!runs.length) { set({ gen: { state: "error", promptId: null, media: [], msg: "No active scenes to generate." } }); return; }
     const reset = _resetSessionPending; _resetSessionPending = false;
@@ -2197,7 +2235,12 @@
       set({ gen: { state: "error", promptId: null, media: [], msg: "No scenes selected." } });
       return;
     }
-    await flushSave();
+    try {
+      await _flushSaveForGenerate();
+    } catch (e) {
+      set({ gen: { state: "error", promptId: null, media: [], msg: _friendlyGenError(e.message) } });
+      return;
+    }
     const runs = _runsForSceneIds(ids);
     if (!runs.length) {
       set({ gen: { state: "error", promptId: null, media: [], msg: "No generatable runs in the selection." } });

movie_editor/server.py

@@ -434,6 +434,17 @@ def _missing_continuity_media(full: Project, target: Project) -> list[str]:
     return missing
 
 
+def _missing_scene_anchor_media(target: Project) -> list[str]:
+    """i2v anchor images referenced on scenes but missing from the media bin."""
+    from .backend.timeline import scene_anchor_media_refs
+
+    missing: list[str] = []
+    for ref in scene_anchor_media_refs(target):
+        if not media.path_for(ref):
+            missing.append(ref)
+    return missing
+
+
 def _attach_scene_anchors(samp: dict, media_pack: Optional[dict], target: Project) -> dict:
     """Mixed-source i2v anchors (Img2Video starting latents), separate from guides."""
     import json
@@ -1174,6 +1185,13 @@ if web is not None and PromptServer is not None:
                 {"detail": f"Missing media for continuity or guide stack ({ids}). Re-upload or clear the reference in Engine settings / Scene inspector."},
                 status=400,
             )
+        missing_anchors = _missing_scene_anchor_media(target)
+        if missing_anchors:
+            ids = ", ".join(missing_anchors)
+            return web.json_response(
+                {"detail": f"Missing i2v anchor image in Media bin ({ids}). Re-save the frame or pick another anchor."},
+                status=400,
+            )
         # V1 uniform chain: if trimmed scenes all agree on a frame count, use it.
         # This makes the timeline trim handle actually affect generation length,
         # provided the user has linked EmptyLTXVLatent.num_frames → Project Frames

movie_editor/tests/test_timeline.py

@@ -380,6 +380,18 @@ def test_stale_identity_pin_ignored_when_auto_off():
     assert continuity_media_refs(p, p) == []
 
 
+def test_scene_anchor_media_refs():
+    p = _project(
+        scenes=[
+            {"text": "a", "source": {"type": "generated_frame", "media_ref": "frame1"}},
+            {"text": "b", "source": {"type": "carry"}},
+        ],
+    )
+    from movie_editor.backend.timeline import scene_anchor_media_refs
+
+    assert scene_anchor_media_refs(p) == ["frame1"]
+
+
 def test_scene_character_media_refs(monkeypatch):
     char_map = {"c1": {"id": "c1", "face_ref": "f1", "body_ref": "b1"}}
     monkeypatch.setattr(