PRES-MGMT Session View — Refactor Plan

**STATUS: ✅ RESOLVED (2026-02-26)**

## Resolution Summary

The "refresh twice" bug was fixed by addressing **two root causes** in the nested data loader chain:

1. **Disabled caching in nested loads**: Changed `try_cache: false` to `try_cache` (preserve parent value) in:
   - `ae_events__event_session.ts` → `_refresh_session_id_background()`
   - `ae_events__event_presentation.ts` → `_refresh_presentation_li_background()`

2. **Missing microtask yields**: Added `await Promise.resolve()` after each `db_save_ae_obj_li__ae_obj()` call to ensure Dexie liveQuery observers fire before functions return.

3. **Fire-and-forget nested loads**: Changed `forEach()` to `await Promise.all()` in presentation loader to block until all presenter loads complete.

**Result:** Session view now renders presentations AND presenters on first load without manual refresh.

**Performance Impact:** Adds ~100-200ms to initial navigation (time to write 1-5 presenter records + microtask yields), but guarantees correct first-render.

**Files Modified:**
- `src/lib/ae_events/ae_events__event_session.ts` (lines 100-107)
- `src/lib/ae_events/ae_events__event_presentation.ts` (lines 187-198)
- `src/lib/ae_events/ae_events__event_presenter.ts` (line 157-161)

**Documentation Updated:**
- `documentation/GUIDE__SvelteKit2_Svelte5_DexieJS.md` - Added "try_cache: false" bug section with detailed explanation
- Code comments added explaining the critical fixes in all modified loader functions
- Journals module updated with microtask yields for consistency (already preserved try_cache correctly)

**Test Status:**
- Manual testing: ✅ Confirmed working (session + presentations + presenters render on first load)
- Playwright test: Created at `tests/coldstart_event_session.test.ts` (requires valid session ID to run)

**Lessons Learned:**
1. **Always preserve `try_cache` through nested data loads** - Disabling caching at any level breaks the entire chain
2. **Add microtask yields after IndexedDB writes** - Ensures liveQuery observers fire before functions return
3. **Block on nested loads with `await Promise.all()`** - Fire-and-forget forEach() causes race conditions
4. **Journals module was already correct** - It preserved `try_cache` for nested entry loads; only added yields for consistency
5. **The existing blocking pattern was sufficient** - No special helper function needed; the bug was in the loader implementation, not the architecture

**What We Implemented:**
We effectively implemented **Option A (Blocking Hydration)** but at a lower level than originally planned. Instead of creating a new `load_session_with_relations()` helper, we fixed the existing loader chain to properly block and cache nested data. The `+page.ts` already used `await` for the session load - it just wasn't working because the underlying loaders weren't caching nested data.

---

## Original Plan (For Reference)

Goal

Make the Presentation Management Session view deterministic on cold-start (empty IndexedDB). The page must render Presentations, Presenters, and Hosted Files without requiring manual refreshes.

Constraints

- Svelte 5 runes and Dexie `liveQuery` behavior (observable recreation, subscription timing).
- Minimize user-perceived latency — keep navigation snappy where possible.
- Avoid large architectural changes unless necessary.

Options (high level)

A) Blocking Hydration (recommended for correctness)
- Block the route `+page.ts` load until the session and all directly required related objects are fetched from the backend and written into IndexedDB. Return `initial_session_obj` in the load data for immediate rendering.
- Pros: simplest to guarantee first-draw correctness; minimal component changes.
- Cons: adds latency to navigation (can be mitigated with optimistic UI or progress indicator).

B) Prefetch Related Records + Hydrate Fallback (hybrid)
- Non-blocking load but `+page.ts` returns `initial_session_obj` and small related-objects payloads (presentations, presenter IDs, hosted_file metadata). Components use these fallbacks while `liveQuery` takes over.
- Pros: keeps navigation responsive; often sufficient.
- Cons: requires careful payload shaping and DB write ordering.

C) Explicit Dependency Chaining in UI (advanced)
- Keep non-blocking loads and use explicit dependency chaining: write session -> await write completion -> then write presentations -> await -> then presenters, ensuring microtask queue flushes between writes. Use targeted `liveQuery` re-creation only when upstream dependency fully resolved.
- Pros: minimal route latency; deterministic ordering.
- Cons: more complex to implement and test.

Recommendation

Start with Option A (Blocking Hydration) for the session page to restore deterministic behavior quickly. After correctness is achieved, consider converting to Option B or C for improved perceived performance if needed.

Detailed Steps (Option A - Blocking Hydration)

1) Add a small helper in `events_func` (e.g., `load_session_with_relations`) that:
   - fetches session by ID from API
   - fetches related presentations (limit/filters as needed)
   - fetches presenters referenced by those presentations (deduplicate IDs)
   - fetches hosted_file metadata for presentation files (if required for the view)
   - writes all results to IndexedDB in a controlled order (session -> presentations -> presenters -> hosted_files)
   - returns a compact `initial_session_obj` payload containing fields needed for first-draw (session, presentation list, presenter summary)

   Implementation note: Use `await db.transaction('rw', db_events.session, db_events.presentation, db_events.presenter, async () => {...})` if atomicity helps. Alternatively write in sequential awaits and call `await Promise.resolve()` after each write to let the microtask queue settle.

2) Update route loader: `src/routes/events/[event_id]/(pres_mgmt)/session/[session_id]/+page.ts` (create if missing) to call and `await` the helper, then return `initial_session_obj` on `data`.

   Example pseudo-code:

   export async function load({ params, parent }) {
     const data = await parent();
     if (browser) {
       const init = await events_func.load_session_with_relations({ api_cfg: data[data.account_id].api, session_id: params.session_id, log_lvl: 0 });
       data.initial_session_obj = init;
     }
     return data;
   }

3) Ensure the page component `+page.svelte` uses the `initial_session_obj` as immediate fallback (it already does in Aether).

4) Add instrumentation logs inside `liveQuery` closures and the helper to verify ordering during QA.

5) Add tests (see below) and manual verification steps.

Alternative (Option B - Hybrid) Implementation Notes

- If you cannot block the route, return an `initial_session_obj` that includes minimal related object arrays (IDs + small metadata) and have `+page.svelte` write those into IDB before mounting heavy child components.
- Use `untrack()` to set selection IDs so stores are updated without causing premature reactivity loops.

Explicit Dependency Chaining (Option C) Notes

- Implement a single `prefetch` function that sequentially performs writes and `await Promise.resolve()` between stages.
- For debugging, add microtask delays (e.g., `await 0`) between writes to observe behaviour.

Testing and Verification

1) Integration test (Playwright recommended)
   - Clear IndexedDB for the app origin.
   - Navigate to `/events/<event_id>/.../session/<session_id>` and assert that the presentation list and presenters are visible within N ms without manual refresh.
   - Repeat on subsequent navigations to ensure no regressions.

2) Unit tests
   - For `events_func.load_session_with_relations`, stub API responses and assert DB writes are made in expected order.

3) Manual QA
   - With a cold profile or after clearing Site storage, navigate to the session page and confirm content is present after the initial navigation and that no manual refreshes are required.

Migration and Rollout

- Implement Option A behind a feature flag if you want to control rollout.
- Short-term: apply Option A to the single problematic route to reduce blast radius.
- Long-term: consider a library-level helper to standardize "blocking prefetch for nested related records" across other pages.

Rollback Plan

- Because changes are additive and limited to one route and helper, revert the `+page.ts` modification and helper call to restore prior behavior.

Deliverables for tomorrow

- `events_func.load_session_with_relations` helper (TS) + unit tests
- Updated `+page.ts` loader for session route to `await` helper and return `initial_session_obj`
- Small test harness / Playwright test that reproduces the cold-start issue and verifies the fix
- Instrumentation logs temporarily enabled for QA

Estimated effort

- Blocking hydration implementation + tests: 2-4 hours
- Hybrid or chaining implementations: additional 2-6 hours depending on thoroughness

Notes about Svelte 5 + Dexie specifics

- Keep `liveQuery` closures stable; capture primitive IDs rather than reactive objects.
- Use `$derived` and `$derived.by` to keep observable instances stable across renders.
- Use `untrack()` when setting selection values to avoid premature subscriptions.
- After DB writes, allowing the microtask queue to settle (`await Promise.resolve()`) helps ensure observers are notified in the expected order during development and debugging.

If you want I can implement Option A for the session route tomorrow (create helper, update loader, add test).