fix(persistence): address PR review feedback (4 low-cost improvements)

From PR #114 external review agent — adopted the real, low-cost findings;
remaining items (false positives / design trade-offs) explained in PR replies:

- coerceEpoch: !Number.isNaN → Number.isFinite — reject ±Infinity, which
  previously slipped through and produced Invalid Date via new Date(Infinity)
- enforceRetentionCap pass2/pass3: decrement overflow only when idbDelete
  actually succeeds — a failed best-effort delete no longer under-evicts
- cloudListStories: explicit column list instead of select() — avoid pulling
  the bulky session_jsonb when only metadata is needed
- Supabase stories: composite primary key (user_id, id) + onConflict user_id,id
  — avoid a cross-user Session.id collision rejecting the second user's save
  (skeleton not yet deployed, so the migration is edited in place)

typecheck + build:cf green.

lib/persistence/cloudStore.ts

@@ -122,7 +122,7 @@ export async function cloudSaveStory(
           deleted_at: null,
           session_jsonb: blob.session,
         },
-        { onConflict: "id" },
+        { onConflict: "user_id,id" },
       )
       .select()
       .single();
@@ -163,9 +163,13 @@ export async function cloudListStories(): Promise<StoryMeta[]> {
   if (!userId) return [];
   try {
     const supabase = await createClient();
+    // Explicit column list (not select()) so the list query doesn't pull the
+    // bulky session_jsonb — rowToMeta only needs the denormalized metadata.
     const { data, error } = await supabase
       .from("stories")
-      .select()
+      .select(
+        "id, world_setting, style_guide, orientation, scene_count, created_at, updated_at",
+      )
       .eq("user_id", userId)
       .is("deleted_at", null)
       .order("updated_at", { ascending: false });

lib/persistence/localStore.ts

@@ -82,8 +82,9 @@ async function enforceRetentionCap(): Promise<void> {
       // Keep records that still owe the cloud a push (pending edits/soft-deletes
       // or a synced baseline) — hard-deleting them would lose that work silently.
       if (r.syncState !== "local-only") continue;
-      await idbDelete(STORIES_STORE, r.id);
-      overflow--;
+      // Only count a slot freed when the delete actually succeeded — a failed
+      // best-effort delete must not decrement overflow (would under-evict).
+      if (await idbDelete(STORIES_STORE, r.id)) overflow--;
     }
 
     // 3. Last-resort: if step 2 couldn't reach the cap, every remaining over-cap
@@ -101,8 +102,7 @@ async function enforceRetentionCap(): Promise<void> {
       for (const r of live) {
         if (overflow <= 0) break;
         if (r.syncState === "local-only") continue; // already evicted in step 2
-        await idbDelete(STORIES_STORE, r.id);
-        overflow--;
+        if (await idbDelete(STORIES_STORE, r.id)) overflow--;
       }
     }
   } catch {

lib/persistence/types.ts

@@ -19,7 +19,9 @@ export const STORY_SCHEMA_VERSION = 1;
  *  crosses a storage/serialization boundary and could arrive as a non-number,
  *  guarding against the historical `t.getTime is not a function` white-screen. */
 export function coerceEpoch(value: unknown, fallback: number): number {
-  if (typeof value === "number" && !Number.isNaN(value)) return value;
+  // Number.isFinite (not just !isNaN) so ±Infinity also falls through to the
+  // fallback — new Date(Infinity).getTime() is NaN, not a usable epoch.
+  if (typeof value === "number" && Number.isFinite(value)) return value;
   const d = value instanceof Date ? value : new Date(value as string | number);
   const t = d.getTime();
   return Number.isNaN(t) ? fallback : t;

supabase/migrations/20260624135618_stories.sql

@@ -16,7 +16,7 @@
 -- dropped-then-created (Postgres has no `create policy if not exists`).
 
 create table if not exists public.stories (
-  id            text primary key,                                  -- = Session.id ("s_xxx"), shared with the local record
+  id            text not null,                                     -- = Session.id ("s_xxx"), unique only per user
   user_id       uuid not null references auth.users (id) on delete cascade,
   world_setting text not null default '',
   style_guide   text not null default '',
@@ -26,7 +26,11 @@ create table if not exists public.stories (
   created_at    timestamptz not null default now(),
   updated_at    timestamptz not null default now(),
   deleted_at    timestamptz,                                       -- soft-delete tombstone; null = live
-  session_jsonb jsonb not null                                     -- slim Session blob (voice + styleReferenceImage stripped)
+  session_jsonb jsonb not null,                                    -- slim Session blob (voice + styleReferenceImage stripped)
+  -- Composite PK: a random Session.id ("s_xxx") is unique only within a user, so
+  -- scope the key by user_id — otherwise a cross-user id collision would reject
+  -- the second user's save with a PK violation.
+  primary key (user_id, id)
 );
 
 -- List query path: a user's stories newest-first.