MAS-WP-0005-T02: SCP-1 quoted local-parts equivalent on receipt

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Assistant: claude-code
Assistant-Model: opus
Assistant-Process: 252470@bnt-lap001
Assistant-Session: ad628c8f-4be2-4979-94c9-76c7ed6f8241

mas-v0.1-spec/CHANGELOG.md

@@ -1,5 +1,11 @@
 # MAS specification changelog
 
+- **SCP-1, quoted equivalence.** A quoted local-part whose content is a
+  valid canonical MAS local-part (no quoted-pairs) is equivalent to the
+  unquoted form. Receivers treat them identically; generators emit the
+  unquoted form; canonical parsers still reject the quoted form (§4).
+  Fixture p1-040 note updated.
+
 ## v0.1.1 (errata, in progress)
 
 Errata from the reference experiment and the live provider test

mas-v0.1-spec/SPECIFICATION.md

@@ -72,6 +72,13 @@ A MAS-aware implementation MAY transport such non-canonical email addresses
 as ordinary email, but MUST NOT claim that they are canonical MAS v0.1
 addresses.
 
+A quoted local-part whose content, after removing the quotes and with no
+quoted-pairs, is a valid canonical MAS local-part is equivalent to that
+unquoted form (RFC 5321 treats unnecessary quoting as equivalent, and MTAs
+remove such quotes in transit). Receivers MUST treat the two identically.
+Generators MUST emit the unquoted form. Parsers that check canonical syntax
+still reject the quoted form.
+
 ### 4.1 Target
 
 A target is non-empty.

mas-v0.1-spec/conformance/addresses.json

@@ -303,7 +303,8 @@
     "local_part": "\"ticket=PR42\"",
     "profile": "p1",
     "valid": false,
-    "error": "quoted local-part outside canonical MAS v0.1"
+    "error": "quoted local-part outside canonical MAS v0.1",
+    "note": "v0.1.1 (SCP-1): not canonical, but a receiver treats it as equivalent to ticket=PR42"
   },
   {
     "id": "p1-041",

mas_conformance/addresses.json

@@ -303,7 +303,8 @@
     "local_part": "\"ticket=PR42\"",
     "profile": "p1",
     "valid": false,
-    "error": "quoted local-part outside canonical MAS v0.1"
+    "error": "quoted local-part outside canonical MAS v0.1",
+    "note": "v0.1.1 (SCP-1): not canonical, but a receiver treats it as equivalent to ticket=PR42"
   },
   {
     "id": "p1-041",

mas_core/parser.py

@@ -141,6 +141,25 @@ def parse_address(value: str) -> ParsedAddress:
     return ParsedAddress(local=parse_local_part(local), domain=domain)
 
 
+def unquote_local_part(local: str) -> str:
+    """Drop quotes a receiver cannot distinguish (v0.1.1, SCP-1).
+
+    `"ticket=PR42"` is not canonical, but RFC 5321 treats it as equivalent to
+    `ticket=PR42` and MTAs strip such quotes, so receivers must too. Quoted
+    content with quoted-pairs or inner quotes is left alone and stays
+    non-canonical.
+    """
+    if len(local) >= 2 and local[0] == local[-1] == '"' and not any(c in '"\\' for c in local[1:-1]):
+        return local[1:-1]
+    return local
+
+
+def parse_received_address(value: str) -> ParsedAddress:
+    """Parse a recipient as a receiver sees it: unnecessary quotes removed."""
+    local, domain = split_address(value)
+    return ParsedAddress(local=parse_local_part(unquote_local_part(local)), domain=domain)
+
+
 @dataclass(frozen=True)
 class ValidationResult:
     ok: bool

mas_gateway/core.py

@@ -22,7 +22,7 @@ from pathlib import Path
 from typing import Callable, Optional
 
 from mas_core.discovery import Discovered, DiscoveryCache, DiscoveryResult, discover
-from mas_core.parser import MasSyntaxError, parse_address
+from mas_core.parser import MasSyntaxError, parse_received_address
 from mas_core.policy import resolve
 from mas_core.statute import build_statute
 
@@ -80,7 +80,7 @@ class Resolver:
 
 def build_event(recipient: str, message: dict, resolver: Resolver) -> dict:
     try:
-        addr = parse_address(recipient)
+        addr = parse_received_address(recipient)
     except MasSyntaxError as e:
         mas = {"valid": False, "error": e.code, "detail": str(e)}
         return {"mas_event_version": EVENT_VERSION, "recipient": recipient, "mas": mas, "message": message}

tests/test_end_to_end.py

@@ -130,8 +130,12 @@ def test_unconfirmed_namespace_is_not_acted_on(env):
 
 def test_non_mas_recipient_still_forwarded(env):
     _, _, _, resolver = env
-    ev = build_event(f'"quoted"@{D}', {}, resolver)
-    assert ev["mas"]["valid"] is False and ev["recipient"] == f'"quoted"@{D}'
+    ev = build_event(f'"not mas"@{D}', {}, resolver)
+    assert ev["mas"]["valid"] is False and ev["recipient"] == f'"not mas"@{D}'
+    # SCP-1: unnecessary quotes are equivalent to the unquoted form
+    ev = build_event(f'"ticket=GS-1"@{D}', {}, resolver)
+    assert ev["mas"]["valid"] is True and ev["mas"]["equivalence_key"] == "ticket=GS-1"
+    assert ev["recipient"] == f'"ticket=GS-1"@{D}'   # the event keeps what arrived
 
 
 def test_pipe_transport_subprocess(env):

tests/test_parser_conformance.py

@@ -12,6 +12,7 @@ from mas_core.parser import (
     MasSyntaxError,
     parse_address,
     parse_local_part,
+    parse_received_address,
     validate_profile,
 )
 
@@ -111,3 +112,23 @@ def test_generator_rules():
             p = parse_local_part(f["local_part"])
             with pytest.raises(MasSyntaxError):
                 generate_local_part(str(p.target), facet=p.facet.value, interaction=p.interaction.mode)
+
+
+@pytest.mark.parametrize("raw, expected", [
+    ('"ticket=PR42"@example.com', "ticket=PR42"),        # SCP-1: unnecessary quotes
+    ('"ticket!callback"@example.com', "ticket!callback"),
+    ("ticket=PR42@example.com", "ticket=PR42"),
+])
+def test_received_quoted_local_part_is_equivalent(raw, expected):
+    assert parse_received_address(raw).local.raw == expected
+
+
+@pytest.mark.parametrize("raw", ['"a\\"b"@example.com', '"a b"@example.com', '"x@y"@example.com'])
+def test_received_quoted_non_mas_stays_invalid(raw):
+    with pytest.raises(MasSyntaxError):
+        parse_received_address(raw)
+
+
+def test_canonical_parser_still_rejects_quotes():
+    with pytest.raises(MasSyntaxError):
+        parse_address('"ticket=PR42"@example.com')

workplans/MAS-WP-0005-spec-errata-v0-1-1.md

@@ -97,6 +97,11 @@ its own task.
   141 tests pass, and the reference parser agrees with all 35 bundle
   fixtures. SCP-2 text corrected: `Ticket=PR42` becomes non-canonical,
   not opaque.
+- 2026-10-18 SCP-1 done: §4 text; `mas_core.parser.unquote_local_part` and
+  `parse_received_address` (receiver side; the canonical parser stays
+  strict); the gateway now parses with them; fixture p1-040 note and
+  CHANGELOG. The end-to-end test now uses a real non-MAS recipient,
+  because `"quoted"@` is equivalent to `quoted@`. 148 tests pass.
 
 ## Reference service: case-robust ticket ids