fix(api): a token hiccup is not "reconnect"; reorders and approvals are one unit each

Deep review of the debt burn:
- `refusal_reason` told the user to reconnect on ANY token-endpoint failure — a 5xx, a 429, a
  misconfigured client — while the grant stayed and the account still read as connected, with no
  connect button. Only `invalid_grant` (the one that drops the grant) means reconnect now.
- `pins.reorder` writes only the rows that change, so two overlapping reorders each skipped rows
  that matched in their own stale snapshot and interleaved into two pins on one slot. It locks the
  user's pins first; the second waits and deals from the first's result.
- Adding a whitelist entry committed the invite and the activation it implies separately, and its
  audit row was written before a new invite had an id (target NULL). One transaction, flushed for
  the id.
- The mutation convention test skipped async routes and dicts returned by name: request-access,
  purge-discovery and the subscription sync answered without `ok`. They do now, and the test
  covers both. The helper-commit check looked only at `_`-names; it reads every non-route
  function, which listed two deliberate committers (upsert_pending_invite, ensure_welcome) — now
  allowlisted with their reasons.

backend/tests/test_route_conventions.py

@@ -23,6 +23,11 @@ COMMITTING_HELPERS = {
     "search.py:_ingest_candidates": "stages around YouTube calls: the stubs must survive an enrich "
     "that fails",
     "search.py:_classify_shorts": "the last stage of that ingest, after its probes",
+    "auth.py:upsert_pending_invite": "commits only when it writes — the contract its three "
+    "callers rely on (`_register_account` persists its own flushed user because a no-op here "
+    "commits nothing)",
+    "messages.py:ensure_welcome": "the websocket push after it must announce a row the client "
+    "can already fetch",
 }
 
 
@@ -31,7 +36,17 @@ def _modules():
         yield path.relative_to(ROUTES).as_posix(), ast.parse(path.read_text(encoding="utf-8"))
 
 
-def _is_mutation_route(fn: ast.FunctionDef) -> bool:
+FUNCTIONS = (ast.FunctionDef, ast.AsyncFunctionDef)
+
+
+def _is_route(fn: ast.FunctionDef | ast.AsyncFunctionDef) -> bool:
+    return any(
+        isinstance(d, ast.Call) and getattr(d.func, "attr", "") in MUTATING | {"get", "websocket"}
+        for d in fn.decorator_list
+    )
+
+
+def _is_mutation_route(fn: ast.FunctionDef | ast.AsyncFunctionDef) -> bool:
     return any(
         isinstance(d, ast.Call) and getattr(d.func, "attr", "") in MUTATING
         for d in fn.decorator_list
@@ -39,27 +54,35 @@ def _is_mutation_route(fn: ast.FunctionDef) -> bool:
 
 
 def test_every_mutation_answers_ok():
-    """`{"ok": true, …}` (or `{"deleted": id}`) for every mutation that answers with a literal —
-    one field a client can read the same way everywhere. A serializer's return is exempt: it
-    describes a resource, not an acknowledgement."""
+    """`{"ok": true, …}` (or `{"deleted": id}`) for every mutation, sync or async — one field a
+    client can read the same way everywhere. A serializer's return (a call) is exempt: it describes
+    a resource, not an acknowledgement. A dict built elsewhere and returned by name is not: it hid
+    two acknowledgements without `ok` from the literal-only scan, so it is spread into a literal."""
     missing = []
     for name, tree in _modules():
         for fn in ast.walk(tree):
-            if not (isinstance(fn, ast.FunctionDef) and _is_mutation_route(fn)):
+            if not (isinstance(fn, FUNCTIONS) and _is_mutation_route(fn)):
                 continue
             for node in ast.walk(fn):
-                if isinstance(node, ast.Return) and isinstance(node.value, ast.Dict):
-                    keys = {k.value for k in node.value.keys if isinstance(k, ast.Constant)}
-                    if not keys & {"ok", "deleted"}:
-                        missing.append(f"{name}:{node.lineno} {fn.name}")
+                if not isinstance(node, ast.Return) or isinstance(node.value, ast.Call):
+                    continue
+                keys = (
+                    {k.value for k in node.value.keys if isinstance(k, ast.Constant)}
+                    if isinstance(node.value, ast.Dict)
+                    else set()
+                )
+                if not keys & {"ok", "deleted"}:
+                    missing.append(f"{name}:{node.lineno} {fn.name}")
     assert missing == []
 
 
 def test_route_helpers_flush_and_leave_the_commit_to_the_handler():
+    """Every function in a route module that is not itself a route is a helper — whatever its name
+    (two public ones committed unseen while this looked only at `_`-names) and sync or async."""
     committing = set()
     for name, tree in _modules():
         for fn in ast.walk(tree):
-            if isinstance(fn, ast.FunctionDef) and fn.name.startswith("_"):
+            if isinstance(fn, FUNCTIONS) and not _is_route(fn):
                 if any(
                     isinstance(n, ast.Call) and getattr(n.func, "attr", "") == "commit"
                     for n in ast.walk(fn)