fix: keep the Key not found prefix so routstr SDK purges dead keys

docs/api/authentication.md

@@ -232,7 +232,7 @@ separately as `key_not_found` (also 401) — see
 {
   "error": {
     "type": "invalid_request_error",
-    "message": "API key not found. Deposit first via /v1/wallet/create to get a key on this node.",
+    "message": "Key not found. Deposit first via /v1/wallet/create to get a key on this node.",
     "code": "key_not_found"
   }
 }

docs/api/errors.md

@@ -129,7 +129,7 @@ by key pruning. This is *not* a formatting problem.
 {
   "error": {
     "type": "invalid_request_error",
-    "message": "API key not found. Deposit first via /v1/wallet/create to get a key on this node.",
+    "message": "Key not found. Deposit first via /v1/wallet/create to get a key on this node.",
     "code": "key_not_found"
   }
 }

routstr/auth.py

@@ -298,11 +298,16 @@ async def _validate_bearer_key_locked(
             # Falling through to the generic handler below would report it as
             # "Invalid API key format", sending callers after a formatting bug
             # that does not exist. Report the real cause instead.
+            #
+            # Keep the "Key not found." prefix verbatim: @routstr/sdk (<=0.4.6)
+            # detects a dead key with a case-sensitive `body.includes("Key not
+            # found")` probe, and uses it to purge the key from its store. The
+            # refund path in balance.py already relies on the same prefix.
             raise HTTPException(
                 status_code=401,
                 detail={
                     "error": {
-                        "message": "API key not found. Deposit first via /v1/wallet/create to get a key on this node.",
+                        "message": "Key not found. Deposit first via /v1/wallet/create to get a key on this node.",
                         "type": "invalid_request_error",
                         "code": "key_not_found",
                     }

tests/unit/test_auth_cashu.py

@@ -350,6 +350,10 @@ async def test_unknown_sk_key_reports_key_not_found(session: AsyncSession) -> No
     assert detail["error"]["type"] == "invalid_request_error"
     assert detail["error"]["code"] == "key_not_found"
     assert "format" not in detail["error"]["message"].lower()
+    # @routstr/sdk (<=0.4.6) purges a dead key on a case-sensitive
+    # `body.includes("Key not found")` probe, so the prefix is part of the
+    # wire contract, not cosmetic.
+    assert detail["error"]["message"].startswith("Key not found.")
 
 
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