fix(mcp): recover truncated prepared proposals

src/gewu/transports/mcp_server.py

@@ -1285,10 +1285,10 @@ def create_mcp_server(
 
         @server.tool(name="proposal_submit", structured_output=False)
         def proposal_submit(proposal_json: str, ctx: Context) -> str:
-            """Validate and submit one bounded typed proposal revision."""
+            """Validate and submit one bounded proposal; report any safe input repair."""
 
             principal = _principal(ctx, identity_provider)
-            proposal = _parse_proposal(proposal_json)
+            proposal, input_repaired = _parse_proposal(proposal_json)
             context = context_provider()
             _authorize_proposal(principal, proposal, context)
             staged_extractions: dict[str, ExtractionRecord] = {}
@@ -1321,6 +1321,7 @@ def create_mcp_server(
                 "status": "accepted" if outcome.receipt else outcome.validation.status,
                 "validation_status": outcome.validation.status,
                 "eligible_for_auto_accept": outcome.validation.eligible_for_auto_accept,
+                "input_repaired": input_repaired,
                 "findings": [
                     finding.model_dump(mode="json") for finding in outcome.validation.findings
                 ],
@@ -1339,8 +1340,20 @@ def create_mcp_server(
                 raise ValueError("Proposal exceeds the supported request size")
             try:
                 draft = json.loads(proposal_json, object_pairs_hook=_reject_duplicate_keys)
-            except (ValueError, TypeError) as error:
-                raise ValueError("Proposal draft must be valid JSON") from error
+            except (ValueError, TypeError):
+                return json.dumps(
+                    {
+                        "status": "invalid",
+                        "issues": [
+                            {
+                                "path": "",
+                                "code": "invalid_proposal_draft",
+                                "message": "Proposal draft must be valid JSON",
+                            }
+                        ],
+                    },
+                    ensure_ascii=False,
+                )
             if not isinstance(draft, dict):
                 raise ValueError("Proposal draft must be a JSON object")
             try:
@@ -1378,10 +1391,36 @@ def create_mcp_server(
 
         @server.tool(name="proposal_evaluate", structured_output=False)
         def proposal_evaluate(proposal_json: str, ctx: Context) -> str:
-            """Evaluate one bounded proposal without storing or publishing it."""
+            """Evaluate one bounded proposal without storing or publishing it.
+
+            A single missing final outer brace is repaired only if the result
+            is valid JSON and matches the full contract. The response exposes
+            input_repaired=true. Other malformed JSON returns status=invalid.
+            A valid proposal may instead return needs-review when an applicable
+            policy requires an owner decision.
+            """
 
             principal = _principal(ctx, identity_provider)
-            proposal = _parse_proposal(proposal_json)
+            try:
+                proposal, input_repaired = _parse_proposal(proposal_json)
+            except ValueError:
+                return json.dumps(
+                    {
+                        "proposal_id": None,
+                        "revision": None,
+                        "status": "invalid",
+                        "eligible_for_auto_accept": False,
+                        "findings": [
+                            {
+                                "code": "PROPOSAL_JSON_INVALID",
+                                "message": "Proposal does not match the GEWU v1 contract",
+                                "path": "proposal_json",
+                            }
+                        ],
+                        "affected_policy_ids": [],
+                    },
+                    ensure_ascii=False,
+                )
             context = context_provider()
             _authorize_proposal(principal, proposal, context)
             staged_extractions: dict[str, ExtractionRecord] = {}
@@ -1408,6 +1447,7 @@ def create_mcp_server(
                     "revision": proposal.revision,
                     "status": report.status,
                     "eligible_for_auto_accept": report.eligible_for_auto_accept,
+                    "input_repaired": input_repaired,
                     "findings": [finding.model_dump(mode="json") for finding in report.findings],
                     "affected_policy_ids": report.affected_policy_ids,
                 },
@@ -1673,17 +1713,32 @@ def _reject_duplicate_keys(pairs: list[tuple[str, object]]) -> dict[str, object]
     return result
 
 
-def _parse_proposal(proposal_json: str) -> ProposalRevision:
+def _parse_proposal(proposal_json: str) -> tuple[ProposalRevision, bool]:
     if len(proposal_json.encode("utf-8")) > 1_000_000:
         raise ValueError("Proposal exceeds the supported request size")
     try:
         parsed = json.loads(proposal_json, object_pairs_hook=_reject_duplicate_keys)
         proposal = ProposalRevision.model_validate_json(proposal_json, strict=True)
+    except json.JSONDecodeError as error:
+        # Tool-call argument serialization can drop the final outer brace while
+        # copying a prepared JSON string. Accept only this unambiguous one-byte
+        # truncation; nested truncation, duplicate keys and schema errors remain
+        # invalid. The response exposes the repair so the caller can report it.
+        candidate = proposal_json.rstrip()
+        if error.pos != len(candidate) or not candidate.startswith("{"):
+            raise ValueError("Proposal does not match the GEWU v1 contract") from error
+        repaired_json = candidate + "}"
+        try:
+            parsed = json.loads(repaired_json, object_pairs_hook=_reject_duplicate_keys)
+            proposal = ProposalRevision.model_validate_json(repaired_json, strict=True)
+        except (ValueError, ValidationError) as repaired_error:
+            raise ValueError("Proposal does not match the GEWU v1 contract") from repaired_error
+        return proposal, True
     except (ValueError, ValidationError) as error:
         raise ValueError("Proposal does not match the GEWU v1 contract") from error
     if not isinstance(parsed, dict):
         raise ValueError("Proposal must be a JSON object")
-    return proposal
+    return proposal, False
 
 
 def _parse_run_request[RequestT: (RunCreateRequest, RunCheckpointRequest)](

tests/api/test_mcp_contribution.py

@@ -252,6 +252,38 @@ def test_mcp_source_to_citation_vertical_slice(tmp_path: Path) -> None:
                     assert prepared_proposal.payload_digest == proposal_payload_digest(
                         prepared_proposal
                     )
+                    truncated_evaluation = await mcp.call_tool(
+                        "proposal_evaluate",
+                        {"proposal_json": prepared_payload["proposal_json"][:-1]},
+                    )
+                    assert not truncated_evaluation.is_error, truncated_evaluation.content
+                    truncated_evaluation_payload = json.loads(
+                        _text_payload(truncated_evaluation)
+                    )
+                    assert truncated_evaluation_payload["proposal_id"] == (
+                        prepared_proposal.proposal_id
+                    )
+                    assert truncated_evaluation_payload["input_repaired"] is True
+                    malformed_prepare = await mcp.call_tool(
+                        "proposal_prepare", {"proposal_json": '{"schema_version":'}
+                    )
+                    assert not malformed_prepare.is_error, malformed_prepare.content
+                    malformed_prepare_payload = json.loads(_text_payload(malformed_prepare))
+                    assert malformed_prepare_payload["status"] == "invalid"
+                    assert malformed_prepare_payload["issues"][0]["code"] == (
+                        "invalid_proposal_draft"
+                    )
+                    malformed_evaluation = await mcp.call_tool(
+                        "proposal_evaluate", {"proposal_json": '{"schema_version":'}
+                    )
+                    assert not malformed_evaluation.is_error, malformed_evaluation.content
+                    malformed_evaluation_payload = json.loads(
+                        _text_payload(malformed_evaluation)
+                    )
+                    assert malformed_evaluation_payload["status"] == "invalid"
+                    assert malformed_evaluation_payload["findings"][0]["code"] == (
+                        "PROPOSAL_JSON_INVALID"
+                    )
                     invalid_draft = json.loads(json.dumps(draft))
                     invalid_evidence = invalid_draft["operations"][1]["node"]["claims"][0][
                         "evidence"
@@ -928,12 +960,13 @@ def test_mcp_source_to_citation_vertical_slice(tmp_path: Path) -> None:
 
                     submitted = await mcp.call_tool(
                         "proposal_submit",
-                        {"proposal_json": candidate.model_dump_json()},
+                        {"proposal_json": candidate.model_dump_json()[:-1]},
                     )
                     assert not submitted.is_error, submitted.content
                     outcome = json.loads(_text_payload(submitted))
                     assert outcome["status"] == "accepted"
                     assert outcome["validation_status"] == "eligible"
+                    assert outcome["input_repaired"] is True
                     assert outcome["receipt"] is not None
                     accepted_head = repository.head()
                     retried = await mcp.call_tool(