feat(signer): migrate Nostr publishing off account.prvkey → resolve_for_wallet (#3)

Closes aiolabs/tasks#3. Pre-cascade prerequisite for aiolabs/lnbits#17
(signer abstraction phase 1), which lands an m002 startup job that
NULLs the legacy `accounts.prvkey` column. After this migration, the
tasks extension reads no plaintext nsec and works with any
NostrSigner backend (LocalSigner / RemoteBunkerSigner / ClientSideOnlySigner).

## What changed

### nostr_hooks.py — three publisher entry points

Was: `_account_keys(wallet_id)` helper pulled `(account.pubkey,
account.prvkey)` from the wallet's owning account, returned None when
prvkey was missing, then passed both to the publishers.

Now: each of `publish_or_delete_task_event`,
`publish_task_completion`, and `publish_completion_delete` calls
`await resolve_for_wallet(...)` (the DRY helper from
aiolabs/lnbits#23 — wallet → account → signer → can_sign-check in
one call, returns None on any soft-fail). The resolved `NostrSigner`
is passed to the publisher. Soft-skip on None (wallet missing,
account unclassified, or ClientSideOnlySigner where the server has
no signing authority).

Removed the `_account_keys` helper entirely.

### nostr_publisher.py — three publishers

Was: `publish_task_to_nostr`, `publish_completion_to_nostr`, and
`publish_completion_delete_to_nostr` each accepted
`(account_pubkey: str, account_prvkey: str)` and signed via a local
`sign_nostr_event` helper that called `coincurve.PrivateKey
.sign_schnorr` directly on the plaintext nsec.

Now: each publisher accepts `signer: NostrSigner`. Signing is
factored into a shared `_sign_and_publish` helper that builds the
unsigned event dict (`kind`/`created_at`/`tags`/`content`), hands it
to `await signer.sign_event(...)`, and writes `id`/`pubkey`/`sig`
back onto the local `NostrEvent` model before publishing. The signer
backend (LocalSigner / RemoteBunkerSigner) is transparent.

Removed the `sign_nostr_event` helper entirely — the signer
abstraction handles all signing now.

Dropped the `coincurve` import; no direct crypto in this extension.

## Acceptance

- [x] `_account_keys` helper removed (nostr_hooks no longer touches account.prvkey)
- [x] all three publishers accept NostrSigner instead of (pubkey, prvkey)
- [x] extension-local Schnorr code removed (sign_nostr_event gone)
- [x] coincurve import dropped
- [x] re-grep `tasks/`: zero `account.prvkey` references
- [x] version bumped: 0.0.1 → 0.0.2 (catalog entry deferred until cascade lands)

Manual smoke testing + tag + catalog entry follow the migration
landing; will run against the regtest stack with lnbits on
`issue-18-phase-2.3` (which validates both LocalSigner and
RemoteBunkerSigner signing paths end-to-end).

## Cross-references

- aiolabs/tasks#3 — issue this commit closes
- aiolabs/lnbits#17 — the cascading signer-abstraction PR
- aiolabs/lnbits#23 — the resolve_for_wallet helper this uses
- aiolabs/lnbits#21 — umbrella audit (5 affected extensions)
- aiolabs/events#23 — sister migration (already on signer-abstraction branch)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

nostr_publisher.py

@@ -9,13 +9,16 @@ Builds:
 - kind 5 deletes referencing either an `a` (for tasks) or `e` tag
   (for completions).
 
-Signs with the wallet owner's Account keypair and publishes via the
-NostrClient wrapping nostrclient's WebSocket.
+Signing routes through the core `NostrSigner` abstraction
+(LocalSigner / RemoteBunkerSigner / ClientSideOnlySigner). The signer
+fills in `id`, `pubkey`, and `sig` per NIP-01 — same serialization
+rules as our local `event_id` property uses, so the returned id
+matches what we'd have computed locally.
 """
 
 import time
 
-import coincurve
+from lnbits.core.signers import NostrSigner
 from loguru import logger
 
 from .models import Task, TaskCompletion
@@ -128,17 +131,30 @@ def build_delete_completion_event(
     return nostr_event
 
 
-def sign_nostr_event(nostr_event: NostrEvent, private_key_hex: str) -> None:
-    privkey = coincurve.PrivateKey(bytes.fromhex(private_key_hex))
-    sig = privkey.sign_schnorr(bytes.fromhex(nostr_event.id))
-    nostr_event.sig = sig.hex()
+async def _sign_and_publish(
+    nostr_client, nostr_event: NostrEvent, signer: NostrSigner
+) -> NostrEvent:
+    """Hand the unsigned event to the signer — it fills in `id`, `pubkey`,
+    and `sig` — then publish through the relay client. Mutates `nostr_event`
+    in place with the canonical signed values."""
+    unsigned = {
+        "kind": nostr_event.kind,
+        "created_at": nostr_event.created_at,
+        "tags": nostr_event.tags,
+        "content": nostr_event.content,
+    }
+    signed = await signer.sign_event(unsigned)
+    nostr_event.id = signed["id"]
+    nostr_event.pubkey = signed["pubkey"]
+    nostr_event.sig = signed["sig"]
+    await nostr_client.publish_nostr_event(nostr_event)
+    return nostr_event
 
 
 async def publish_task_to_nostr(
     nostr_client,
     task: Task,
-    account_pubkey: str,
-    account_prvkey: str,
+    signer: NostrSigner,
     *,
     delete: bool = False,
 ) -> NostrEvent | None:
@@ -147,12 +163,11 @@ async def publish_task_to_nostr(
         return None
     try:
         nostr_event = (
-            build_delete_task_event(task, account_pubkey)
+            build_delete_task_event(task, signer.pubkey)
             if delete
-            else build_task_event(task, account_pubkey)
+            else build_task_event(task, signer.pubkey)
         )
-        sign_nostr_event(nostr_event, account_prvkey)
-        await nostr_client.publish_nostr_event(nostr_event)
+        await _sign_and_publish(nostr_client, nostr_event, signer)
         logger.info(
             f"[TASKS] Published {'delete' if delete else '31922 task'} "
             f"{nostr_event.id[:16]}... (kind {nostr_event.kind})"
@@ -167,18 +182,16 @@ async def publish_completion_to_nostr(
     nostr_client,
     task_address: str,
     completion: TaskCompletion,
-    account_pubkey: str,
-    account_prvkey: str,
+    signer: NostrSigner,
 ) -> NostrEvent | None:
     if not nostr_client:
         logger.debug("[TASKS] No NostrClient available, skipping publish")
         return None
     try:
         nostr_event = build_completion_event(
-            task_address, completion, account_pubkey
+            task_address, completion, signer.pubkey
         )
-        sign_nostr_event(nostr_event, account_prvkey)
-        await nostr_client.publish_nostr_event(nostr_event)
+        await _sign_and_publish(nostr_client, nostr_event, signer)
         logger.info(
             f"[TASKS] Published 31925 completion {nostr_event.id[:16]}... "
             f"(status: {completion.task_status})"
@@ -192,15 +205,13 @@ async def publish_completion_to_nostr(
 async def publish_completion_delete_to_nostr(
     nostr_client,
     completion_id: str,
-    account_pubkey: str,
-    account_prvkey: str,
+    signer: NostrSigner,
 ) -> NostrEvent | None:
     if not nostr_client:
         return None
     try:
-        nostr_event = build_delete_completion_event(completion_id, account_pubkey)
-        sign_nostr_event(nostr_event, account_prvkey)
-        await nostr_client.publish_nostr_event(nostr_event)
+        nostr_event = build_delete_completion_event(completion_id, signer.pubkey)
+        await _sign_and_publish(nostr_client, nostr_event, signer)
         logger.info(
             f"[TASKS] Published completion delete {nostr_event.id[:16]}..."
         )