fix(sync): classify transfer-need by explicit join intent + auto-request source so approval prompt appears

[khokonm]

Symptom (after #10)

The new device now connects, but immediately shows "Connected" + the device list and never asks to sync, so the old device gets no approve/deny prompt. On refresh the new device briefly shows "Connecting…" again.

Root cause — "needs a transfer?" was inferred, not declared

Whether a joining device should pull the existing notes was being guessed from proxies that don't actually mean "this device is a member of the chain":

• fix(sync): fix stuck-on-Connecting (wiped sync code) + device-role classification #10 used hasData (does the device hold any local notes). But a fresh device usually does have a note (a seed/empty note, or something typed before joining), so hasData was true → the server marked it already-established → it never requested a transfer → the old device never got a prompt. That's the "immediately Connected" behavior.
• The earlier cursor === 0 proxy was wrong in the opposite direction (the origin has cursor 0).

The only reliable signal is explicit intent: did this device generate the code (it's the origin/source) or enter a code to join (it must bootstrap from an existing device)? That's a per-chain fact the device knows and must remember.

Fix — persisted per-chain intent + auto-request

1. Client declares its role. New notes-sync-initialized-room localStorage key records the chain (roomId) this device has bootstrapped. A device is "initialized" when it generated the code or finished receiving a transfer. join now sends needsTransfer = !initializedForThisRoom instead of hasData.
   • enableSync(..., { initialized: true }) on generate; { initialized: false } on entering a code.
   • On transfer completion, the device marks itself initialized → it won't ask again and reconnects as a full member (fixes the "Connecting… again after refresh / asks forever" loop).
2. Server trusts the declaration. isNewDevice = clientNeedsTransfer && otherDevices.length > 0 (replacing the hasData/cursor guess). This drives the welcome needsTransfer, the catch-up-ops gate, and the fix(sync): show device-approval prompt after reconnect (replay pending transfers) #8 approval-replay gate.
3. Auto-request the source. When a device still needs its initial copy and an existing device is online, it now automatically sends the transfer request (on welcome and when a device comes online), so the approve/deny prompt appears on the existing device without the user manually picking a source. The "Choose a source device" picker remains as an override for multi-device setups. Self-guarded so it never fires while a transfer is pending/in progress.

Files changed

• src/utils/sync.ts — per-chain initialized flag + helpers; buildJoinPayload sends needsTransfer; welcome uses client-authoritative needsTransfer; maybeAutoRequestTransfer() on welcome + device-joined; mark initialized on transfer completion; enableSync intent param; clear flag on disable.
• src/components/SettingsPanel.tsx — pass { initialized: true } on generate, { initialized: false } on join.
• server/src/index.ts — classify role from msg.needsTransfer; protocol doc comment.

Where the prompt appears

On the device that generated the code / holds the notes: a full-screen "Allow sync to ?" modal (Deny/Approve) and a "Transfer Request" card under Settings → Sync. With auto-request, you no longer need to tap a source on the new device — just keep both apps open.

Verification

• Traced: enter code → enableSync({initialized:false}) → join needsTransfer:true → server isNewDevice:true → welcome → auto-request → old device shows approval → approve → chunks → new device marks initialized → subsequent joins are needsTransfer:false ("Connected").
• Not run locally: tsc/build/lint — sandbox has no installed toolchain for either workspace and installs are blocked (registry 403). Changes use only existing in-scope symbols; requestTransferFromDevice is a hoisted function declaration referenced by maybeAutoRequestTransfer.

Manual test plan

1. Device A: enable sync → Generate. Status should be Connected (A is the source).
2. Device B (fresh): enter the code with both apps open. Within a moment, A shows the approve/deny prompt automatically (no tapping on B).
3. Approve on A → B receives notes and shows Connected.
4. Refresh B → it reconnects to Connected (does not ask to sync again, no stuck "Connecting…").
5. Deny on A → B shows the picker so you can retry; pick A again → prompt reappears on A.
6. Multi-device: with a 3rd device, the "Choose a source device" picker still lets you select which device to copy from.