fix: bound model stream aggregation and close failed responses

artemis/llm/argument_fingerprint.py

@@ -16,12 +16,38 @@ class ArgumentFingerprint:
         self.encoding_valid = True
         self.digest = hashlib.sha256()
         self.prefixes: list[dict] = []
+        self.whitespace_chars = 0
+        self.whitespace_run = 0
+        self.max_whitespace_run = 0
+        self.min_delta_chars: int | None = None
+        self.max_delta_chars = 0
+        self.same_delta_run = 0
+        self.max_same_delta_run = 0
+        self.previous_delta_digest: bytes | None = None
 
     def observe(self, arguments: str) -> None:
         self.characters += len(arguments)
         if not arguments:
             return
         self.deltas += 1
+        length = len(arguments)
+        self.min_delta_chars = min(self.min_delta_chars or length, length)
+        self.max_delta_chars = max(self.max_delta_chars, length)
+        for character in arguments:
+            if character in " \t\r\n":
+                self.whitespace_chars += 1
+                self.whitespace_run += 1
+                self.max_whitespace_run = max(self.max_whitespace_run, self.whitespace_run)
+            else:
+                self.whitespace_run = 0
+        # One digest, never the previous argument body. Surrogate handling here
+        # compares SDK strings only; wire UTF-8 fingerprints remain invalid below.
+        delta_digest = hashlib.sha256(arguments.encode("utf-8", "surrogatepass")).digest()
+        self.same_delta_run = (
+            self.same_delta_run + 1 if delta_digest == self.previous_delta_digest else 1
+        )
+        self.max_same_delta_run = max(self.max_same_delta_run, self.same_delta_run)
+        self.previous_delta_digest = delta_digest
         if not self.encoding_valid:
             return
         try:
@@ -50,4 +76,11 @@ class ArgumentFingerprint:
             "argument_deltas": self.deltas,
             "argument_prefixes": [dict(prefix) for prefix in self.prefixes],
             "argument_encoding_valid": self.encoding_valid,
+            "argument_json_whitespace_chars": self.whitespace_chars,
+            "argument_json_whitespace_run": self.whitespace_run,
+            "argument_json_whitespace_run_max": self.max_whitespace_run,
+            "argument_delta_chars_min": self.min_delta_chars,
+            "argument_delta_chars_max": self.max_delta_chars,
+            "argument_same_delta_run": self.same_delta_run,
+            "argument_same_delta_run_max": self.max_same_delta_run,
         }