diff --git a/docs/validation/mcp-shell-combined-cli-20261004.tar.gz b/docs/validation/mcp-shell-combined-cli-20261004.tar.gz
new file mode 100644
index 0000000000..ecbf3b8740
Binary files /dev/null and b/docs/validation/mcp-shell-combined-cli-20261004.tar.gz differ
diff --git a/docs/validation/mcp-shell-derived-diagnostic-20261004.rst b/docs/validation/mcp-shell-derived-diagnostic-20261004.rst
new file mode 100644
index 0000000000..68ddd18ce2
--- /dev/null
+++ b/docs/validation/mcp-shell-derived-diagnostic-20261004.rst
@@ -0,0 +1,235 @@
+Closed-journal MCP shell exit1 investigation
+==========================================
+
+Singer owns OpenHCS response/JSON diagnostic receiving; python-introspect's
+declaration decoder is a shared dependency seam being coordinated with Dewey.
+Root394/541 source/units and merged567 native semantics remain independent.
+
+Pinned currentmain2df0918353b47fa07d19fe4b6cc8b52b5e4c1695. Existing checkout
+was reused on a new branch after567 closed; six foreign dirty gitlinks and all
+untracked originals remain untouched. Open PRs394/404/472/494/518/522/541/468
+have no active dev-client shell/result implementation claim. Current394 file
+census has no dev_client, dto/functions or serialization/json crossing.
+
+Original engineering567/public94-attempt01/mcp.stdout records eight public
+operation receipts with empty visible errors; original shell ends terminal1.
+No new client/native process or request was used to determine the cause.
+
+Actual original qualified target8513 decoder applied offline to all eight closed
+receipts: seven decode without error; registration-status becomes
+McpDevPayloadFailure with mcp_payload_invalid/ValueError:
+CustomFunctionRegistrationObservation received undeclared field(s): outcome.
+
+Original python-introspect.dataclass_from_mapping only admits init=True fields.
+Observation.outcome is declared init=False and derived from publication/saved
+proofs in __post_init__; original to_jsonable emits all dataclass fields.
+The same nominal declaration therefore serializes a field its decoder rejects.
+McpDevToolResult.has_errors correctly sees the rejection; persistent shell
+aggregates that returncode. The custom McpDevPayloadFailure JSON projector emits
+only receipt, deleting rejection diagnostics from visible JSON. This explains
+the exit1 without alleging native registration/status/close failure.
+
+Original read-only diagnostic script/logs remain under engineering567/
+public94-attempt01/DIAGNOSE-CLOSED-RESULTS01.py/.stdout/.stderr: terminal0,
+4.12s,236672KiB peakRSS,Swap0; no sockets or source/image execution.
+Actual original dev_client_core.py SHA256
+2aaaffec501e901352192ed35016caa6ce00122b429e41b3f7c8683eb3fd1aed;
+target01/python_introspect/dataclass_projection.py SHA256
+82662ff8eaa4f2aeb3b33edd61abae57020a7f139c3aa396d82dcecf8b801160.
+
+Required relation and owner destination
+---------------------------------------
+
+One declaration must drive encode/decode of derived fields. Constructor inputs
+remain constructor-owned; supplied derived wire values must be checked against
+the actual constructed result, not dropped, assigned or allowed to override it.
+Unknown fields and mismatched derived proofs must fail closed. Reuse the original
+python-introspect decoder, not a consumer-specific outcome pop/type switch or
+alternative codec. BOUND-1/2/8 apply at this declaration boundary.
+
+The existing McpDevToolResult/McpDevPayloadFailure owns failed-decode diagnostics
+and original receipt. JSON, formatted output, returncode and persistent aggregate
+must project that same owned failure, not silently serialize success while
+retaining hidden exit1. No error suppression/--allow-error-payloads workaround.
+
+Acceptance after coherent implementation: original closed status receipt decodes
+to the declared observation with exact matching proofs, shell returns0 for those
+unchanged successful receipts; genuinely malformed/mismatched/new declaration
+cases retain original receipt and visible typed diagnostics with nonzero exit.
+Use complete relevant AST/dependency/consumer evidence before production edits;
+focused original user entrypoint verification last, no mutation replay/new client.
+
+Working diagnostic checkpoint
+-----------------------------
+
+Deleted the five-line McpDevPayloadFailure serializer that returned only the
+native receipt. The original canonical dataclass serializer now exposes the
+same declared receipt/errors record used by returncode and formatted output.
+The existing failure declaration rejects an empty diagnostic cause. The original
+McpDevToolResult decoder restores this common rejection record through the same
+dataclass_from_mapping codec, so a JSON batch roundtrip keeps the original cause
+once rather than hiding it or wrapping a second rejection. No raw-shape parser,
+business-leaf switch, codec, status flag or registry was added.
+
+Source qualification used the existing viewer-retirement-519/run_source_controls.py
+bootstrap: OpenHCS source activation first, then read-only paired startup and Qt
+backing before their consumers. SHELL-DIAGNOSTIC-CONTROLS02 passed20, terminal0,
+6.91s wall,270032KiB peakRSS,Swap0. It exercised strict producer decode, independent
+capability/MRO behavior, visible JSON cause plus unchanged receipt, batch roundtrip,
+and original transport failure ownership. No server/native operation was launched.
+The previous CONTROLS01 collection failure from unmatched foreign Qt backing is
+preserved, not rewritten. The two plugin-free pytest configuration warnings are
+retained in the original output.
+
+Complete source evidence reused the original audit.Package/Repository tooling:
+704 OpenHCS modules parsed with zero omissions;40 relevant full module ASTs,
+plus12 original qualified python-introspect module ASTs with zero omissions.
+SHELL-FAMILY01.jsonl/.stderr retain declarations, imports, writes and consumers.
+Actual census terminal0,13.06s,538200KiB peakRSS,Swap0; this is source evidence,
+not a complete NRA R1 ownership proof and not a <=512MiB claim. The transport
+derived-field census finds Observation.outcome as the sole init=False field in
+agent/MCP DTOs; internal cache/lock/thread init=False fields are not alternate
+registration status authorities.
+
+Remaining: the shared python-introspect declaration decoder still rejects the
+original successful derived outcome. Dewey was asked for the existing dependency
+owner implementation/release; no foreign dependency checkout or gitlink was
+edited. This diagnostic checkpoint makes that original cause visible, but does
+not yet claim successful observation CLI roundtrip or corrected shell terminal0.
+The original native positive and original shell terminal1 remain separate facts.
+
+Consumer closure and shared-code disposition
+-------------------------------------------
+
+The related sampling, pipeline/artifact-plan and UI-action JSON assertions now
+retain the entire original rejected receipt AND assert its typed diagnostic
+projection, instead of asserting the removed diagnostic-erasing shape. No
+success assertion or nonzero exit assertion was weakened. The real
+McpDevClient.execute pipeline command check retains its original controlled
+wire peer and production command/framing/rendering/returncode path.
+
+CONSUMERS03 retained its original terminal1:62 passed/11 failed. Five failures
+identified additional old failure-shape assertions, now migrated. Four were the
+existing sibling test-module import under importlib mode; the original test
+directory is explicitly on PYTHONPATH for CONSUMERS04. Two were an existing
+UI-test global serializer monkeypatch captured by subsequently imported knowledge
+renderer aliases; the independent UI and pipeline/sampling qualifications are
+kept distinct rather than changing production serialization to tolerate it.
+CONSUMERS03's12 UI controls passed. CONSUMERS04's pipeline/sampling61 controls
+passed, terminal0, including the affected real execute boundary. Original raw
+failure and successful output/timing remain byte-exact in the archive.
+
+Original unmodified debt_census.py against main2df0918 and production8fbba870f,
+exact sole changed production file openhcs/mcp/dev_client_core.py: all measured
+debt deltas zero, code lines+3, zero parse omissions, terminal0,0.56s wall,
+25016KiB peakRSS,Swap0. R0 is a syntax ratchet, not live/whole NRA proof.
+
+Dewey explicitly confirmed no released dependency checkout: the foreign
+python-introspect source has active transitive borrowers even though its child
+tree is clean. He forwarded the exact original-decoder requirement to Parent
+integration. Singer has not edited that checkout or its gitlink. The remaining
+shared hunk is dataclass_from_mapping's declared-field algorithm: admit all
+declared names, construct only init fields, decode supplied derived values with
+the same annotation mechanism, compare with actual post-construction owner
+values, and reject contradictions. project_dataclass remains a constructor-field
+projection that intentionally recomputes target-derived facts; it is not a wire
+decoder and must not be turned into a second status authority.
+
+No installed CLI terminal0 claim yet: the original native reply needs that codec
+integration before its successful derived outcome can roundtrip. The diagnostic
+source checkpoint works independently and does not claim recovery/replay of any
+UNKNOWN operation. Planck's disjoint Shapes geometry ownership was confirmed;
+522 selection/lifecycle and541 Root units ownership remain untouched.
+
+Reviewed dependency and actual CLI receiving
+-------------------------------------------
+
+The preceding dependency-release blocker is historical. Parent owns the distinct
+python-introspect checkout and PR10. Source reviewed at ee0b65f and final
+ac7b2388ed800649a8d0157f00056471a466dd20: dataclasses.fields owns membership;
+get_type_hints(include_extras=True) and the existing recursive annotation decoder
+own input conversion; only init fields reach the constructor. Supplied non-init
+values are compared with validated actual constructed values, never assigned.
+Omitted derived fields are legal; contradictory values and unknown fields fail
+closed. No outcome special case, mirrored field roster or second codec exists.
+Equality retains the field owner's existing Python equality contract; this is
+not an array-specific comparison extension. No concrete defect found in review.
+
+Read-only codec source selected after original OpenHCS source activation, before
+any consumers, through the existing source bootstrap. Actual imported codec:
+/home/ts/wt/python-introspect-derived-decode-20261004/src/python_introspect/
+dataclass_projection.py, SHA256
+d2be277051b070d73503025a3addcde8016787e18a369c45b60be0c0edb65fea.
+The receiving process imported version0.1.15 at fad3cbb. Exact source diff to
+ac7b238's0.1.16 changes only __version__ in src/python_introspect/__init__.py;
+the tested decoder and all other source algorithms are byte-identical. No
+foreign gitlink, installed dependency or existing scientific target was changed.
+
+SHELL-COMBINED-CLI05 retained terminal1:17 source controls passed, including the
+new independent derived declaration using inherited cooperative describe hooks,
+omitted derived fields and contradiction rejection without generic consumers
+being edited. Four receiving cases failed before wire dispatch because the new
+fixture mistakenly supplied --no-resident-server instead of the original
+--no-resident option. This was a known harness error, not native UNKNOWN.
+Original log retained:7.24s wall,261568KiB peakRSS,Swap0. The corrected fixture
+also consumes the real pretty-printed JSON documents through stdlib JSONDecoder.
+
+Only the four affected receiving cases ran in SHELL-COMBINED-CLI06. All passed:
+normal dev_client.main -> persistent shell -> original McpDevClient.start/execute
+and command/framing/DTO decoding -> canonical JSON -> shell aggregate returncode.
+Only the transport context/peer is controlled, reusing the existing pipeline
+ControlledWireSession. Process launches are forbidden by the fixture. Exact
+original command arguments/tool order and complete saved replies are retained.
+No old process was contacted, no source was evaluated, no native operation or
+registration was replayed, and no new MCP/native/client subprocess was started.
+
+The eight original successful replies yield shell terminal0. The original
+registration observation is the declared DTO with registered outcome, zero
+errors, one published source and its exact persisted proof; canonical projection
+equals the entire original status receipt. The three copied malformed replies
+(contradictory outcome, boolean outcome, undeclared field) each yield terminal1,
+visible mcp_payload_invalid/ValueError cause and the full original receipt with
+the single explicit test mutation. Native receipt errors remain empty; local
+decode errors remain a separate fact. Re-decoding canonical batches retains the
+same cause once and nonzero status.
+
+Actual controls06 terminal0,4PASS,5.73s wall,254896KiB peakRSS,Swap0. Full canonical
+CLI outputs and per-case statuses are in the raw stdout, not just test assertions.
+No successful17-control repeat or7GiB installed cold import occurred. Before this
+source batch, original resource check read9.3GiB available, critical warnings
+for existing swap/disk, full-memory PSI avg10=.24 then .17. This receipt reports
+actual measured resource cost, not a new hard cap or scientific admission rule.
+
+The real closed native TCP journey remains the accepted merged567 evidence;
+this acceptance establishes its corrected source CLI decoding/rendering/exit
+path with a controlled closed-reply peer. It does not claim a fresh installed
+0.1.16 client/native journey or recovery of an uncertain mutation. Public
+dependency0.1.16 publication and future bundle projection remain Dewey's release
+ownership. Existing OpenHCS dependency floor is still >=0.1.14; original metadata
+owner must carry the corrected minimum for ordinary future installation.
+
+Ordinary installation requirement
+--------------------------------
+
+Parent explicitly released the narrow pyproject.toml metadata hunk into579
+after python-introspect0.1.16 publication. The canonical production requirement
+is now python-introspect>=0.1.16,<0.2, excluding earlier decoders that reject
+derived fields and preserving the breaking-series bound. This supersedes the
+historical floor dependency above. Dewey/518 received the exact requirement
+coordination so later metadata integration must retain0.1.16 rather than0.1.15.
+No gitlink, ObjectState requirement, vendoring or installed package changed.
+
+Dewey's existing PUBLISHED-PYPI-PROOF.rst records workflow37174368240SUCCESS at
+merge430fbbeeb6c7e0a9274d3bf9b0998a10cae5a505 and exact public wheel/sdist source
+identity. Publication is not installed receiving. The four-case CLI acceptance
+and production R0 evidence above are unchanged; no full tests/build/import or
+scientific target mutation was repeated for this one-line metadata correction.
+
+SHELL-METADATA-FLOOR07 uses the original read_project/read_release_candidate and
+CandidateRequirementCompatibility owner, not another requirements parser:
+0.1.14/0.1.15 excluded,0.1.16/0.1.17 admitted,0.2.0 excluded; actual candidate
+floor/compatibility proofs true. Terminal0,0.19s wall,26444KiB peakRSS,Swap0.
+Original raw command/output remains in engineering567/public94-attempt01.
+Root's sole518 metadata ownership was rechecked via the current PR/comments;
+the precise one-line hunk and future430 source-pin boundary were addressed
+directly on518. His broader branch and release family remain unedited.
diff --git a/docs/validation/mcp-shell-derived-diagnostic-controls-20261004.tar.gz b/docs/validation/mcp-shell-derived-diagnostic-controls-20261004.tar.gz
new file mode 100644
index 0000000000..87e80ca013
Binary files /dev/null and b/docs/validation/mcp-shell-derived-diagnostic-controls-20261004.tar.gz differ
diff --git a/openhcs/mcp/dev_client_core.py b/openhcs/mcp/dev_client_core.py
index 2dc3ae1d8b..cdebef180c 100644
--- a/openhcs/mcp/dev_client_core.py
+++ b/openhcs/mcp/dev_client_core.py
@@ -407,10 +407,9 @@ class McpDevPayloadFailure:
     receipt: JsonValue
     errors: tuple[AgentError, ...]
 
-
-@to_jsonable.register(McpDevPayloadFailure)
-def _jsonable_payload_failure(value: McpDevPayloadFailure) -> JsonValue:
-    return value.receipt
+    def __post_init__(self) -> None:
+        if not self.errors:
+            raise ValueError("A rejected MCP payload requires its diagnostic cause.")
 
 
 @dataclass(frozen=True, slots=True)
@@ -451,7 +450,13 @@ def _decode_payload(payload, contracts):
                 rejections.append(
                     AgentError.from_exception("mcp_payload_invalid", error)
                 )
-        return McpDevPayloadFailure(payload, (*_agent_errors(payload), *rejections))
+        # The local rejection is a declared transport record too. Its canonical
+        # dataclass projection retains both cause and original native receipt.
+        # Recover that record through the same codec, not another error parser.
+        try:
+            return dataclass_from_mapping(McpDevPayloadFailure, payload)
+        except (TypeError, ValueError):
+            return McpDevPayloadFailure(payload, (*_agent_errors(payload), *rejections))
 
     def first_decoded_payload(self):
         """A missing or rejected payload is not a successful empty record."""
diff --git a/pyproject.toml b/pyproject.toml
index ff8fd15e1f..94c4cf162b 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -102,7 +102,7 @@ dependencies = [
     "zmqruntime>=0.3.0,<0.4",
     "pycodify>=0.1.3,<0.2",
     "objectstate>=1.1.8,<2",
-    "python-introspect>=0.1.14,<0.2",
+    "python-introspect>=0.1.16,<0.2",
     "metaclass-registry>=0.2.2,<0.3",
     "arraybridge>=0.3.6,<0.4",
     "polystore>=0.3.0,<0.4",
diff --git a/tests/unit/agent/test_mcp_dev_client_declared_decoder.py b/tests/unit/agent/test_mcp_dev_client_declared_decoder.py
index 29eeebe3dc..814a97e9e0 100644
--- a/tests/unit/agent/test_mcp_dev_client_declared_decoder.py
+++ b/tests/unit/agent/test_mcp_dev_client_declared_decoder.py
@@ -1,7 +1,8 @@
 """Original successful native receipt, replayed offline: NEVER start a process."""
-from dataclasses import dataclass
+from dataclasses import dataclass, field
 import json
 from pathlib import Path
+import sys
 
 import pytest
 
@@ -9,7 +10,7 @@
 from openhcs.agent.dto.common import AgentError, AgentResultEnvelope, SCHEMA_VERSION
 from openhcs.agent.dto.execution import RuntimeBootstrapState, RuntimeBootstrapHandle
 from openhcs.mcp.dev_client_core import (
-    McpDevToolBatchResponse, McpDevToolResult, McpDevPayloadFailure,
+    McpDevToolBatchResponse, McpDevToolResult, McpDevPayloadFailure, McpDevServerSpec,
     state_surface_document, state_surface_payload, ui_bridge_operation_result,
     workflow_result_payload,
 )
@@ -70,6 +71,43 @@ def test_renderless_new_declaration_decodes_and_executes_cooperative_mro():
     assert result.decoded_for_rendering().first_decoded_payload() is value
 
 
+@dataclass(frozen=True, kw_only=True)
+class DerivedRenderlessResult(RenderlessResult):
+    description: str = field(init=False)
+
+    def __post_init__(self):
+        object.__setattr__(self, "description", self.describe())
+
+
+class DerivedRenderlessCapability(RenderlessCapability):
+    name = "openhcs_decoder_derived_case578"
+    cli_command = "decoder-derived-case578"
+    output_contract = DerivedRenderlessResult
+
+
+def test_independent_derived_declaration_executes_existing_cooperative_hooks():
+    original = DerivedRenderlessResult(schema_version=SCHEMA_VERSION, fact=DeclaredFact(value="owned"))
+    wire = to_jsonable(original)
+    result = McpDevToolResult(DerivedRenderlessCapability.name, False, (wire,)).decoded_for_rendering()
+    value = result.first_decoded_payload()
+    assert value == original and value.description == "independent:owned"
+    assert value.describe() == "independent:owned"
+    assert not result.has_errors()
+    del wire["description"]
+    omitted = McpDevToolResult(DerivedRenderlessCapability.name, False, (wire,)).decoded_for_rendering()
+    assert omitted.first_decoded_payload() == original
+
+
+def test_independent_derived_claim_cannot_override_cooperative_owner():
+    original = DerivedRenderlessResult(schema_version=SCHEMA_VERSION, fact=DeclaredFact(value="owned"))
+    wire = {**to_jsonable(original), "description": "override"}
+    result = McpDevToolResult(DerivedRenderlessCapability.name, False, (wire,)).decoded_for_rendering()
+    assert result.has_errors() and result.first_decoded_payload() is None
+    assert isinstance(result.payloads[0], McpDevPayloadFailure)
+    assert result.payloads[0].receipt == wire
+    assert "disagrees" in result.diagnostic_errors()[0].message
+
+
 def test_renderless_malformed_record_is_rejected_with_original_receipt():
     raw = {"schema_version": SCHEMA_VERSION, "fact": {}}
     result = McpDevToolResult(RenderlessCapability.name, False, (raw,)).decoded_for_rendering()
@@ -79,6 +117,28 @@ def test_renderless_malformed_record_is_rejected_with_original_receipt():
     assert result.decoded_for_rendering().payloads[0] is result.payloads[0]
 
 
+def test_json_rejection_preserves_cause_receipt_and_original_batch_roundtrip():
+    raw = {"schema_version": SCHEMA_VERSION, "fact": {}}
+    result = McpDevToolResult(RenderlessCapability.name, False, (raw,)).decoded_for_rendering()
+    batch = McpDevToolBatchResponse.from_results(McpDevServerSpec(sys.executable), (result,))
+    wire = to_jsonable(batch)
+    rejection = wire["results"][0]["payloads"][0]
+    assert rejection["receipt"] == raw
+    assert rejection["errors"] == to_jsonable(result.diagnostic_errors())
+    assert rejection["errors"][0]["code"] == "mcp_payload_invalid"
+    restored = McpDevToolBatchResponse.for_rendering(wire)
+    assert restored.has_errors()
+    assert restored.diagnostic_errors() == batch.diagnostic_errors()
+    assert len(restored.diagnostic_errors()) == 1
+    assert restored.results[0].payloads[0].receipt == raw
+    assert isinstance(restored.results[0].payloads[0], McpDevPayloadFailure)
+
+
+def test_rejection_declaration_cannot_claim_failure_without_a_cause():
+    with pytest.raises(ValueError, match="diagnostic cause"):
+        McpDevPayloadFailure(receipt={}, errors=())
+
+
 @pytest.mark.parametrize("raw", (
     {"schema_version": SCHEMA_VERSION, "fact": {"value": "owned"}, "unknown": True},
     {"schema_version": SCHEMA_VERSION, "fact": {"value": "owned", "unknown": True}},
diff --git a/tests/unit/agent/test_mcp_dev_client_pipeline_results.py b/tests/unit/agent/test_mcp_dev_client_pipeline_results.py
index 19d34b9c38..6a12dcf66c 100644
--- a/tests/unit/agent/test_mcp_dev_client_pipeline_results.py
+++ b/tests/unit/agent/test_mcp_dev_client_pipeline_results.py
@@ -439,7 +439,9 @@ def test_malformed_contract_is_explicit_and_keeps_entire_receipt(broken):
     failed = response.results[0].payloads[0]
     assert isinstance(failed, McpDevPayloadFailure)
     assert failed.receipt == broken
-    assert to_jsonable(failed) == broken
+    rejection = to_jsonable(failed)
+    assert rejection["receipt"] == broken
+    assert rejection["errors"] == to_jsonable(failed.errors)
     assert response.has_errors()
     rendered = PipelineArtifactPlanRenderer.render(response)
     assert "mcp_payload_invalid" in rendered and "unavailable" in rendered
@@ -793,7 +795,13 @@ def forbidden_raw_failure_scan(value):
     finally:
         client.close()
     assert execution.returncode == int(malformed)
-    assert execution.payload["results"][0]["payloads"][0] == receipt
+    payload = execution.payload["results"][0]["payloads"][0]
+    if malformed:
+        assert payload["receipt"] == receipt
+        assert len(payload["errors"]) == 1
+        assert payload["errors"][0]["code"] == "mcp_payload_invalid"
+    else:
+        assert payload == receipt
     assert (
         "mcp_payload_invalid" if malformed else "Owned step"
     ) in execution.rendered_output
diff --git a/tests/unit/agent/test_mcp_dev_client_sampling_results.py b/tests/unit/agent/test_mcp_dev_client_sampling_results.py
index b76cdd2550..b9c853ce8c 100644
--- a/tests/unit/agent/test_mcp_dev_client_sampling_results.py
+++ b/tests/unit/agent/test_mcp_dev_client_sampling_results.py
@@ -190,7 +190,9 @@ def test_malformed_receipt_never_becomes_successful_empty_sample(receipt):
     response = McpDevToolBatchResponse.from_results(McpDevServerSpec(sys.executable), (result,))
     assert isinstance(result.payloads[0], McpDevPayloadFailure)
     assert result.payloads[0].receipt == receipt
-    assert to_jsonable(response)["results"][0]["payloads"][0] == receipt
+    rejection = to_jsonable(response)["results"][0]["payloads"][0]
+    assert rejection["receipt"] == receipt
+    assert rejection["errors"] == to_jsonable(result.diagnostic_errors())
     text = PlateImageSampleRenderer.render(response)
     assert "mcp_payload_invalid" in text
     assert "Image:" not in text
diff --git a/tests/unit/agent/test_mcp_dev_client_ui_action_results.py b/tests/unit/agent/test_mcp_dev_client_ui_action_results.py
index ae9c1b3980..1c6066c40a 100644
--- a/tests/unit/agent/test_mcp_dev_client_ui_action_results.py
+++ b/tests/unit/agent/test_mcp_dev_client_ui_action_results.py
@@ -157,7 +157,9 @@ async def controlled_wire(args):
     assert dev_client.main(["selected-workflow", "run_plate"]) == 1
     assert "mcp_payload_invalid" in capsys.readouterr().out
     assert dev_client.main(["selected-workflow", "run_plate", "--json"]) == 1
-    assert json.loads(capsys.readouterr().out)["results"][0]["payloads"][0] == malformed
+    rejection = json.loads(capsys.readouterr().out)["results"][0]["payloads"][0]
+    assert rejection["receipt"] == malformed
+    assert rejection["errors"] == to_jsonable(result.diagnostic_errors())
 
 
 def test_poll_presentation_rejects_row_missing_declared_state_field():
diff --git a/validation/registration-observation-567/test_closed_cli_roundtrip.py b/validation/registration-observation-567/test_closed_cli_roundtrip.py
new file mode 100644
index 0000000000..3b5532695b
--- /dev/null
+++ b/validation/registration-observation-567/test_closed_cli_roundtrip.py
@@ -0,0 +1,107 @@
+"""Receive closed engineering replies offline through the original CLI.
+
+Only the wire peer is controlled; never reconnect to or replay a native mutation.
+"""
+from contextlib import asynccontextmanager
+from io import StringIO
+import json
+from pathlib import Path
+import shlex
+
+import pytest
+
+from test_mcp_dev_client_pipeline_results import ControlledWireSession
+from openhcs.agent.dto.functions import CustomFunctionRegistrationObservation
+from openhcs.mcp import dev_client
+from openhcs.mcp.dev_client_core import McpDevPayloadFailure, McpDevToolBatchResponse
+from openhcs.serialization.json import to_jsonable
+
+
+ROOT = Path('/home/ts/wt/openhcs-issue-batch-20260929/engineering567/public94-attempt01')
+
+
+@pytest.mark.parametrize('mutation,message', (
+    (None, None),
+    ({'outcome': 'not_observed'}, 'disagrees with its constructed value'),
+    ({'outcome': True}, 'must be one of'),
+    ({'extra': 'not declared'}, 'undeclared field'),
+))
+def test_saved_native_success_and_declared_contradictions_through_normal_shell(
+    monkeypatch, capsys, mutation, message,
+):
+    receipts = json.loads((ROOT / 'PUBLIC-REPLIES-FINAL01.json').read_text())
+    original_lines = (ROOT / 'ADMIN_REGISTRATION56794/author-workspace/output/runtime/mcp.stdin').read_text().splitlines()
+    commands = tuple(line for line in original_lines if line.startswith('call '))
+    assert len(commands) == len(receipts) == 8
+    assert tuple(shlex.split(line)[1] for line in commands) == tuple(row['tool'] for row in receipts)
+    status_index = next(index for index, row in enumerate(receipts)
+                        if row['tool'] == 'openhcs_get_custom_function_registration_status')
+    original_status = json.loads(json.dumps(receipts[status_index]['payloads'][0]))
+    if mutation is not None:
+        commands = (commands[status_index],)
+        receipts = [receipts[status_index]]
+        receipts[0]['payloads'][0].update(mutation)
+    peer = ControlledWireSession(tuple(row['payloads'][0] for row in receipts))
+
+    @asynccontextmanager
+    async def closed_wire_peer(*args, **kwargs):
+        yield peer
+
+    def forbidden_launch(*args, **kwargs):
+        raise AssertionError('Closed-reply acceptance must never launch a process')
+
+    import asyncio
+    import subprocess
+    monkeypatch.setattr(asyncio, 'create_subprocess_exec', forbidden_launch)
+    monkeypatch.setattr(asyncio, 'create_subprocess_shell', forbidden_launch)
+    monkeypatch.setattr(subprocess, 'Popen', forbidden_launch)
+    monkeypatch.setattr(dev_client, 'open_mcp_dev_session', closed_wire_peer)
+    monkeypatch.setattr('sys.stdin', StringIO('\n'.join((*commands, 'exit', ''))))
+    # main -> persistent shell -> original client lifecycle/execute -> actual
+    # command/session/framing/DTO codec -> canonical JSON -> shell returncode.
+    terminal = dev_client.main(['shell', '--no-resident', '--no-prompt'])
+    output = capsys.readouterr()
+    assert not output.err
+    batches = []
+    remaining = output.out.lstrip()
+    decoder = json.JSONDecoder()
+    while remaining:
+        batch, end = decoder.raw_decode(remaining)
+        batches.append(batch)
+        remaining = remaining[end:].lstrip()
+    assert len(batches) == len(commands)
+    assert tuple(call[0] for call in peer.calls) == tuple(row['tool'] for row in receipts)
+    for command, call in zip(commands, peer.calls):
+        arguments = shlex.split(command)
+        assert call[1] == json.loads(arguments[arguments.index('--arguments') + 1])
+    if mutation is None:
+        assert terminal == 0
+        for batch in batches:
+            restored = McpDevToolBatchResponse.for_rendering(batch)
+            assert not restored.has_errors()
+            assert not restored.diagnostic_errors()
+        restored_status = McpDevToolBatchResponse.for_rendering(batches[status_index])
+        value = restored_status.results[0].first_decoded_payload()
+        assert isinstance(value, CustomFunctionRegistrationObservation)
+        assert to_jsonable(value) == original_status
+        assert value.outcome.value == 'registered'
+        assert len(value.published_sources) == 1
+        assert value.persisted_source is not None
+    else:
+        assert terminal == 1
+        rejection = batches[0]['results'][0]['payloads'][0]
+        assert rejection['receipt'] == {**original_status, **mutation}
+        assert rejection['receipt']['errors'] == []
+        assert len(rejection['errors']) == 1
+        cause = rejection['errors'][0]
+        assert cause['code'] == 'mcp_payload_invalid'
+        assert cause['exception_type'] == 'ValueError'
+        assert message in cause['message']
+        restored = McpDevToolBatchResponse.for_rendering(batches[0])
+        assert restored.has_errors()
+        assert isinstance(restored.results[0].payloads[0], McpDevPayloadFailure)
+        assert to_jsonable(restored.diagnostic_errors()) == rejection['errors']
+    # Preserve full canonical user output and actual exit, not only assertions.
+    print(json.dumps({'case': mutation, 'terminal': terminal,
+                      'controlled_wire_calls': len(peer.calls)}))
+    print(output.out, end='')