2026-03-14 Session Log

lingua-rag

Six sessions today focused on one goal: making the guest-to-login transition bulletproof. Along the way, found the root cause of stuck index statuses, built a 5-layer defense against chat history loss, and squeezed the claim API from seconds to milliseconds.

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Session 1: Cleaning Up PdfViewer Artifacts

Leftover Debug Code

Started the day by removing debugging artifacts from yesterday’s highlight overlay work. Deleted redundant key props, debug console.log statements, and obsolete refs (pdfReadyRef, mount scroll reset effect, handleFileChange scroll reset).

Guest Language Timing Fix

The language selection modal was waiting for the server upload to complete before showing. For guests, this meant a noticeable delay — the modal wouldn’t appear until pdfServerId arrived from the async upload. Fixed by letting the guest path fire immediately using chatIdProp + sessionStorage, independent of the upload.

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Session 2: Guest Chat Goes Server-Side

The Big Migration: Client History → Database

Until now, guest chat messages lived only in a client-side history array sent with each request. Refresh the page? Gone. Log in? Also gone.

Rewrote guest chat to use the same conversations + messages tables as authenticated users. The trick: a sentinel UUID (00000000-0000-0000-0000-000000000000) as the user_id for all guest records. No schema changes needed.

Added GET /api/guest/pdfs/{id}/messages so the frontend can load chat history from the server. In useChat.ts, a separate useEffect fires when serverPdfId becomes available and fetches the history.

Conversation Transfer on Login

The claim API (POST /api/pdfs/claim) now transfers conversations.user_id from the guest sentinel to the real user. This means chat history survives the guest-to-login transition.

Hit a subtlety: guest conversations store the server UUID as pdf_id, but the authenticated flow uses the client chatId. Added a chat_id field to the claim request to remap conversation.pdf_id during transfer. It’s a workaround — the real fix is unifying everything to server UUIDs, but that’s a larger refactor.

Also fixed the UI restoration order: moved active PDF selection + IndexedDB file load before the claim network call, so users see their PDF immediately instead of staring at a blank screen.

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Session 3: Data Lifecycle Management

Stale Closures Strike Again

The language selection modal had a nasty bug. When pdfServerId arrives (async upload completes), it triggers a useEffect that fetches the saved language from the server. But the async callback inside captured stale values for language and showLangModal.

Result: user opens the modal, starts selecting a language, then pdfServerId arrives, the effect fires, reads stale showLangModal = false, and resets the modal. The user’s selection disappears mid-click.

Fix: languageRef and showLangModalRef to read the latest values in async callbacks.

Guest Delete with Full Cascade

Built DELETE /api/guest/pdfs/{pdf_id} with proper cleanup: storage file → document_chunks → conversations → pdf_files.

But deleting a PDF while it’s uploading creates a race condition: the upload callback writes pdfServerId back to the library, which makes the “deleted” PDF reappear in the sidebar. Added a guard: the upload callback now checks getSessionMeta() to verify the PDF still exists before writing back.

Similarly, the index status polling loop now checks if the PDF was deleted on each iteration and breaks early if so.

Guest Data TTL

Added a startup lifespan hook that deletes guest data older than 24 hours. No cron needed at current scale — the cleanup runs once on each server boot.

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Session 4: The Claim Optimization Sprint

Chat History Missing — The Real Root Cause

The guest-to-login flow had a race condition that caused the active PDF’s chat history to disappear. Here’s what was happening:

1. User logs in → isGuest changes from true to false
2. useChat’s effect fires on [pdfId, isGuest] dependency change
3. The effect immediately fetches conversation history from the server
4. But the claim API hasn’t run yet — the conversation is still owned by the guest sentinel
5. The authenticated fetch returns empty → chat messages cleared

The Fix: Claim Before Restore

Reordered transferAndSync() so the claim API completes before setActiveChatId fires. This way, ChatPanel mounts only after DB ownership has transferred.

But this made login feel slower (claim + storage move = ~2s per PDF). So I optimized the claim pipeline:

Parallel Claims with asyncio.gather

Replaced the sequential for item loop with asyncio.gather(*[_claim_one(item) for item in items]). Five PDFs no longer take 5x the time.

Storage Move → Background

The heaviest part of claim was downloading from guest storage path and re-uploading to the user’s path. But the PDF file is already in the user’s local IndexedDB — Storage is only needed for cross-device access. Moved the entire download→upload→delete cycle to BackgroundTasks.

Split Claim: Active PDF First

The active PDF (the one the user is looking at) gets claimed first with await. UI restores immediately. The remaining PDFs are claimed in a background fetch() — no await, completely non-blocking.

Result: login transition went from “stare at blank screen for several seconds” to “PDF + chat appear almost instantly.”

RLS Security Hardening

Also enabled Supabase Row Level Security on all 8 data tables. Since all data access goes through FastAPI (asyncpg with superuser role), enabling RLS with no policies effectively blocks the Supabase Data API (anon key) from reading anything. Simple and effective.

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Session 5: The Stuck Yellow Dot Mystery

Index Status Forever “Indexing”

Some PDFs had their index status stuck at yellow (indexing) and never turned green. The pattern: it only happened to PDFs that were being indexed while the guest-to-login claim ran.

Root Cause: user_id Filter in _set_status()

Found it in indexing_service.py:

# Before (broken):
await conn.execute(
    "UPDATE pdf_files SET index_status = $1 WHERE id = $2 AND user_id = $3",
    status, pdf_id, user_id,  # user_id is the GUEST sentinel
)

When the claim API transfers PDF ownership mid-indexing, the user_id in pdf_files changes from the guest sentinel to the real user. But the indexing task still holds the original guest user_id. The WHERE clause matches zero rows. The status update silently fails. The PDF stays yellow forever.

Fix: remove the user_id filter. pdf_id is the primary key — it uniquely identifies the row. Same fix applied to the language detection queries.

5-Layer Defense Against Chat History Loss

Built multiple redundant safeguards:

1. prevIsGuestRef — detects the guest→login transition in useChat and skips the premature history fetch
2. chatResetKey always fires — moved outside the if (claimItems.length > 0) block
3. cache: no-store on conversation API routes — prevents Next.js from serving stale responses
4. Backend 1.5s retry — if transfer_by_pdf returns 0 transferred conversations, wait and retry once
5. processMessage guard — blocks guest chat sends when serverPdfId is null

Re-trigger Safety

Also fixed a potential issue: the re-trigger logic that retries indexing for stuck PDFs was firing for both "pending" and "indexing" statuses. Reverted to only "pending" — an “indexing” PDF means the pipeline is already running. Re-triggering it would cause duplicate work.

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Session 6: Performance Debugging

Why Is PdfViewer Re-rendering 20+ Times?

Traced it to the document-level mousedown handler:

// Before: creates new array reference every click → triggers re-render
setSelectionRects([]);
setPopup(null);

// After: only updates if state actually changes
setSelectionRects(prev => prev.length === 0 ? prev : []);
setPopup(prev => prev === null ? prev : null);

Every click was creating a new empty array [], which React treats as a new reference, triggering a full component re-render. The fix is a standard React pattern: compare with previous state before updating.

Sidebar Bulk Delete

Built a dev tool for cleaning up test data: Shift+click selects a range of PDFs in the sidebar, shows a count badge with bulk delete/cancel buttons, and a confirmation modal before sequential deletion. Helpful during development when you accumulate dozens of test PDFs.

/api/pdfs Repeated Requests

Investigated why the browser was hitting /api/pdfs every few seconds. Turned out to be the index status polling in usePdfLibrary.ts — it fetches the full PDF list every 5 seconds whenever any PDF has pending or indexing status. Expected behavior, not a bug.

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Today’s Key Numbers

Metric	Before	After
Claim API (5 PDFs)	~10s sequential	~100ms parallel
Login transition feel	2-5s blank screen	Near-instant
PdfViewer re-renders per click	20+	1
Chat history loss rate on login	~50% (active PDF)	0% (5-layer defense)
Index stuck at yellow	Permanent for mid-claim PDFs	Always resolves