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_hooks.py

@@ -14,21 +14,6 @@ from .nostr_publisher import (
 )
 
 
-async def _account_keys(wallet_id: str) -> tuple[str, str] | None:
-    """Fetch (pubkey, prvkey) for the wallet's owning account. Returns None
-    when the account is missing keys, so callers can skip cleanly."""
-    from lnbits.core.crud.users import get_account
-    from lnbits.core.crud.wallets import get_wallet
-
-    wallet_obj = await get_wallet(wallet_id)
-    if not wallet_obj:
-        return None
-    account = await get_account(wallet_obj.user)
-    if not account or not account.pubkey or not account.prvkey:  # type: ignore[attr-defined]
-        return None
-    return account.pubkey, account.prvkey  # type: ignore[attr-defined]
-
-
 async def publish_or_delete_task_event(
     task: Task, *, delete: bool = False
 ) -> None:
@@ -37,15 +22,16 @@ async def publish_or_delete_task_event(
     Errors are logged and swallowed so a Nostr outage doesn't break the
     HTTP flow that triggered the publish."""
     try:
+        from lnbits.core.signers import resolve_for_wallet
+
         from . import nostr_client
 
-        keys = await _account_keys(task.wallet)
-        if not keys:
+        signer = await resolve_for_wallet(task.wallet)
+        if signer is None:
             return
-        pubkey, prvkey = keys
 
         nostr_event = await publish_task_to_nostr(
-            nostr_client, task, pubkey, prvkey, delete=delete
+            nostr_client, task, signer, delete=delete
         )
         if nostr_event and not delete:
             task.nostr_event_id = nostr_event.id
@@ -62,15 +48,16 @@ async def publish_task_completion(
     caller can persist it as the completion's primary key, replacing the
     locally-generated hash from the optimistic insert."""
     try:
+        from lnbits.core.signers import resolve_for_wallet
+
         from . import nostr_client
 
-        keys = await _account_keys(task.wallet)
-        if not keys:
+        signer = await resolve_for_wallet(task.wallet)
+        if signer is None:
             return None
-        pubkey, prvkey = keys
 
         nostr_event = await publish_completion_to_nostr(
-            nostr_client, task.address, completion, pubkey, prvkey
+            nostr_client, task.address, completion, signer
         )
         return nostr_event.id if nostr_event else None
     except Exception as exc:
@@ -83,15 +70,16 @@ async def publish_completion_delete(
 ) -> None:
     """Publish a NIP-09 delete for a previously-published completion."""
     try:
+        from lnbits.core.signers import resolve_for_wallet
+
         from . import nostr_client
 
-        keys = await _account_keys(wallet_id)
-        if not keys:
+        signer = await resolve_for_wallet(wallet_id)
+        if signer is None:
             return
-        pubkey, prvkey = keys
 
         await publish_completion_delete_to_nostr(
-            nostr_client, completion_id, pubkey, prvkey
+            nostr_client, completion_id, signer
         )
     except Exception as exc:
         logger.warning(f"[TASKS] Nostr completion delete failed: {exc}")