feat(backend): add CycloneParseError and CycloneValidationError

backend/src/cyclone/parsers/exceptions.py

@@ -0,0 +1,28 @@
+"""Exception types raised by the parser.
+
+These are reserved for unrecoverable, file-level failures (bad envelope, no
+ISA segment, malformed delimiters). Per-claim validation issues are not
+exceptions — they are accumulated into ``ValidationReport``.
+"""
+
+from __future__ import annotations
+
+
+class CycloneParseError(Exception):
+    """Raised when the file itself cannot be parsed (bad envelope, etc.)."""
+
+    def __init__(self, message: str, *, segment_index: int | None = None) -> None:
+        self.segment_index = segment_index
+        suffix = f" (segment {segment_index})" if segment_index is not None else ""
+        super().__init__(f"{message}{suffix}")
+
+
+class CycloneValidationError(Exception):
+    """Raised by the CLI for envelope-level validation failures (no claims found)."""
+
+    def __init__(self, message: str, *, rule_id: str | None = None, claim_id: str | None = None) -> None:
+        self.rule_id = rule_id
+        self.claim_id = claim_id
+        prefix = f"[{rule_id}] " if rule_id else ""
+        claim = f" (claim {claim_id})" if claim_id else ""
+        super().__init__(f"{prefix}{message}{claim}")