connector-reasoning-item fix: cargo fmt

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

README.md

@@ -13,6 +13,9 @@ Crate `crates/model-connector`:
 
 - `src/contract.rs` - the v3 wire contract (`gamecult.model.*.v3`): `ProviderRequest`, `TransportInvocation`,
   `TransportResult`, `TransportReceipt`, the typed `StopReason`, `FailureKind` and `Refusal`,
+  `InputItem::ReasoningState` (a provider's opaque reasoning block, replayed by callers
+  verbatim via `TransportResult::transcript_items`; the service refuses another provider's
+  state in the in-flight tool exchange and drops it from earlier turns),
   and the canonical byte and digest functions that bind a result to its request. Every
   document is named MessagePack with unknown fields refused.
 - `src/envelope.rs` - the AES-256-GCM `TransportEnvelope` (binary ciphertext), its

crates/model-connector/src/contract.rs

@@ -7,7 +7,7 @@ use sha2::{Digest, Sha256};
 use thiserror::Error;
 use zeroize::Zeroize;
 
-use crate::envelope::ServiceError;
+use crate::envelope::{ServiceError, binary_schema};
 
 pub const PROVIDER_REQUEST_SCHEMA_ID: &str = "gamecult.model.provider_request.v3";
 pub const INVOCATION_SCHEMA_ID: &str = "gamecult.model.transport_invocation.v3";
@@ -124,6 +124,17 @@ impl ProviderRequest {
                     require_provider_call_id(call_id, "input.call_id")?;
                     require_content(output, "input.output")?;
                 }
+                InputItem::ReasoningState {
+                    provider,
+                    model,
+                    state,
+                } => {
+                    require_id(provider, "input.provider")?;
+                    require_id(model, "input.model")?;
+                    if state.is_empty() {
+                        return Err(ContractError::Invalid("input.state"));
+                    }
+                }
             }
         }
         Ok(())
@@ -210,6 +221,18 @@ pub enum InputItem {
         call_id: String,
         output: String,
     },
+    /// One provider reasoning block, opaque to every caller: `state` is the
+    /// connector's own encoding of the whole block. Callers replay it
+    /// verbatim in transcript order and never inspect or branch on it; only
+    /// the connector of `provider` reads it, and the service drops or refuses
+    /// the state of any other provider before a backend sees the request.
+    ReasoningState {
+        provider: String,
+        model: String,
+        #[serde(with = "serde_bytes")]
+        #[schemars(schema_with = "binary_schema")]
+        state: Vec<u8>,
+    },
 }
 
 #[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize, JsonSchema)]
@@ -303,15 +326,14 @@ impl TransportResult {
         }
     }
 
-    pub fn transported(
+    /// Built by `ProviderCall` in the daemon and by in-crate tests only; the
-        invocation: &TransportInvocation,
+    /// result's identity is its receipt's.
-        events: Vec<TransportEvent>,
+    #[cfg(any(test, feature = "daemon"))]
-        receipt: TransportReceipt,
+    pub(crate) fn transported(events: Vec<TransportEvent>, receipt: TransportReceipt) -> Self {
-    ) -> Self {
         Self {
             schema_id: RESULT_SCHEMA_ID.to_string(),
-            request_id: invocation.request_id().to_string(),
+            request_id: receipt.request_id.clone(),
-            caller_runtime_id: invocation.caller_runtime_id.clone(),
+            caller_runtime_id: receipt.caller_runtime_id.clone(),
             disposition: TransportDisposition::Transported {
                 events,
                 receipt: Box::new(receipt),
@@ -319,6 +341,53 @@ impl TransportResult {
         }
     }
 
+    /// The transcript items a completed result adds, ready to append to the
+    /// next request verbatim: consecutive text deltas become one assistant
+    /// text, a tool call stays a tool call and reasoning state is stamped with
+    /// the receipt's provider and model. A refused or failed result yields
+    /// none, because a partial reasoning block must never be replayed.
+    pub fn transcript_items(&self) -> Vec<InputItem> {
+        let TransportDisposition::Transported { events, receipt } = &self.disposition else {
+            return Vec::new();
+        };
+        if !matches!(receipt.outcome, TransportOutcome::Completed { .. }) {
+            return Vec::new();
+        }
+        let mut items: Vec<InputItem> = Vec::new();
+        let mut text = String::new();
+        for event in events {
+            if !matches!(event.payload, TransportEventPayload::TextDelta { .. }) && !text.is_empty()
+            {
+                items.push(InputItem::AssistantText {
+                    text: std::mem::take(&mut text),
+                });
+            }
+            match &event.payload {
+                TransportEventPayload::TextDelta { text: delta } => text.push_str(delta),
+                TransportEventPayload::ToolCall {
+                    call_id,
+                    name,
+                    arguments,
+                } => items.push(InputItem::ToolCall {
+                    call_id: call_id.clone(),
+                    name: name.clone(),
+                    arguments: arguments.clone(),
+                }),
+                TransportEventPayload::ReasoningState { state } => {
+                    items.push(InputItem::ReasoningState {
+                        provider: receipt.provider.clone(),
+                        model: receipt.model.clone(),
+                        state: state.clone(),
+                    })
+                }
+            }
+        }
+        if !text.is_empty() {
+            items.push(InputItem::AssistantText { text });
+        }
+        items
+    }
+
     pub fn validate_against(&self, invocation: &TransportInvocation) -> Result<(), ContractError> {
         if self.schema_id != RESULT_SCHEMA_ID {
             return Err(ContractError::Schema);
@@ -353,6 +422,14 @@ pub enum TransportEventPayload {
         name: String,
         arguments: String,
     },
+    /// One reasoning block of the provider that answered. It carries no
+    /// provider or model: the receipt names them, so a backend cannot tag its
+    /// own state.
+    ReasoningState {
+        #[serde(with = "serde_bytes")]
+        #[schemars(schema_with = "binary_schema")]
+        state: Vec<u8>,
+    },
 }
 
 #[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize, JsonSchema)]
@@ -375,6 +452,12 @@ impl TransportEvent {
                 require_id(name, "event.tool_name")?;
                 require_content(arguments, "event.arguments")
             }
+            TransportEventPayload::ReasoningState { state } => {
+                if state.is_empty() {
+                    return Err(ContractError::Invalid("event.state"));
+                }
+                Ok(())
+            }
         }
     }
 }
@@ -389,6 +472,9 @@ pub struct TransportReceipt {
     pub provider_request_sha256: [u8; 32],
     pub model: String,
     pub provider: String,
+    /// How many foreign `ReasoningState` items the service removed from the
+    /// request before the backend saw it.
+    pub foreign_reasoning_dropped: u32,
     pub outcome: TransportOutcome,
 }
 
@@ -454,6 +540,10 @@ pub enum Refusal {
     Indeterminate,
     ReplayConflict,
     Malformed,
+    // A `ReasoningState` of another provider sits in the in-flight tool
+    // exchange, where dropping it would break the provider's own rules. A plain
+    // comment: a doc comment would split the published schema into a union.
+    ForeignReasoningState,
 }
 
 /// The one wire codec of every v3 document: named MessagePack (struct fields
@@ -677,7 +767,6 @@ mod tests {
     fn transported_result_binds_identity_digest_and_event_order() {
         let invocation = invocation();
         let result = TransportResult::transported(
-            &invocation,
             vec![TransportEvent {
                 sequence: 0,
                 payload: TransportEventPayload::ToolCall {
@@ -738,7 +827,7 @@ mod tests {
             ]
         );
         let invocation = invocation();
-        let result = TransportResult::transported(&invocation, Vec::new(), receipt(&invocation));
+        let result = TransportResult::transported(Vec::new(), receipt(&invocation));
         let TransportDisposition::Transported { receipt: sent, .. } = &result.disposition else {
             unreachable!()
         };
@@ -784,7 +873,7 @@ mod tests {
     #[test]
     fn an_unknown_field_is_refused_not_dropped() {
         let invocation = invocation();
-        let result = TransportResult::transported(&invocation, Vec::new(), receipt(&invocation));
+        let result = TransportResult::transported(Vec::new(), receipt(&invocation));
         let TransportDisposition::Transported { receipt: sent, .. } = &result.disposition else {
             unreachable!()
         };
@@ -876,7 +965,7 @@ mod tests {
     #[test]
     fn validate_against_refuses_each_identity_field() {
         let invocation = invocation();
-        let result = TransportResult::transported(&invocation, Vec::new(), receipt(&invocation));
+        let result = TransportResult::transported(Vec::new(), receipt(&invocation));
         assert_eq!(result.validate_against(&invocation), Ok(()));
         let mut other_request = result.clone();
         other_request.request_id = "request-2".to_string();
@@ -903,4 +992,118 @@ mod tests {
             );
         }
     }
+
+    fn reasoning(state: &[u8]) -> TransportEventPayload {
+        TransportEventPayload::ReasoningState {
+            state: state.to_vec(),
+        }
+    }
+
+    fn event(sequence: u64, payload: TransportEventPayload) -> TransportEvent {
+        TransportEvent { sequence, payload }
+    }
+
+    fn text(delta: &str) -> TransportEventPayload {
+        TransportEventPayload::TextDelta {
+            text: delta.to_string(),
+        }
+    }
+
+    fn tool_call() -> TransportEventPayload {
+        TransportEventPayload::ToolCall {
+            call_id: "call-9".to_string(),
+            name: "read_source".to_string(),
+            arguments: "{}".to_string(),
+        }
+    }
+
+    #[test]
+    fn transcript_items_follow_event_order() {
+        let invocation = invocation();
+        let events = vec![
+            event(0, text("one ")),
+            event(1, text("two")),
+            event(2, reasoning(&[0x80, 0xff])),
+            event(3, tool_call()),
+            event(4, text("three")),
+            event(5, reasoning(&[7])),
+        ];
+        let result = TransportResult::transported(events, receipt(&invocation));
+        assert_eq!(
+            result.transcript_items(),
+            vec![
+                InputItem::AssistantText {
+                    text: "one two".to_string()
+                },
+                InputItem::ReasoningState {
+                    provider: "fixture-sse".to_string(),
+                    model: invocation.request.model.clone(),
+                    state: vec![0x80, 0xff],
+                },
+                InputItem::ToolCall {
+                    call_id: "call-9".to_string(),
+                    name: "read_source".to_string(),
+                    arguments: "{}".to_string(),
+                },
+                InputItem::AssistantText {
+                    text: "three".to_string()
+                },
+                InputItem::ReasoningState {
+                    provider: "fixture-sse".to_string(),
+                    model: invocation.request.model.clone(),
+                    state: vec![7],
+                },
+            ]
+        );
+    }
+
+    #[test]
+    fn transcript_items_of_refused_or_failed_are_empty() {
+        let invocation = invocation();
+        let refused = TransportResult::refused(&invocation, Refusal::OutputBound);
+        assert_eq!(refused.transcript_items(), Vec::new());
+
+        let mut failed = receipt(&invocation);
+        failed.outcome = TransportOutcome::Failed {
+            kind: FailureKind::RateLimited,
+            message: "slow down".to_string(),
+        };
+        let partial = TransportResult::transported(
+            vec![event(0, text("half")), event(1, reasoning(&[1, 2, 3]))],
+            failed,
+        );
+        assert_eq!(partial.transcript_items(), Vec::new());
+    }
+
+    #[test]
+    fn reasoning_state_validation() {
+        let item = |provider: &str, model: &str, state: &[u8]| InputItem::ReasoningState {
+            provider: provider.to_string(),
+            model: model.to_string(),
+            state: state.to_vec(),
+        };
+        let validate = |item: InputItem| {
+            let mut request = request();
+            request.input.push(item);
+            request.validate()
+        };
+        assert_eq!(validate(item("anthropic", "claude", &[1])), Ok(()));
+        assert_eq!(
+            validate(item("", "claude", &[1])),
+            Err(ContractError::Invalid("input.provider"))
+        );
+        assert_eq!(
+            validate(item("anthropic", "", &[1])),
+            Err(ContractError::Invalid("input.model"))
+        );
+        assert_eq!(
+            validate(item("anthropic", "claude", &[])),
+            Err(ContractError::Invalid("input.state"))
+        );
+        assert_eq!(event(0, reasoning(&[1])).validate(), Ok(()));
+        assert_eq!(
+            event(0, reasoning(&[])).validate(),
+            Err(ContractError::Invalid("event.state"))
+        );
+    }
 }

crates/model-connector/src/envelope.rs

@@ -37,12 +37,13 @@ pub struct TransportEnvelope {
     pub ciphertext: Vec<u8>,
 }
 
-/// The ciphertext is MessagePack `bin` on the wire, never an array of integers.
+/// Raw bytes are MessagePack `bin` on the wire, never an array of integers.
-fn binary_schema(_: &mut schemars::SchemaGenerator) -> schemars::Schema {
+/// Serves the ciphertext and both reasoning states.
+pub(crate) fn binary_schema(_: &mut schemars::SchemaGenerator) -> schemars::Schema {
     schemars::json_schema!({
         "type": "string",
         "format": "binary",
-        "description": "MessagePack bin: the raw ciphertext bytes, never an array of integers"
+        "description": "MessagePack bin: raw bytes, never an array of integers"
     })
 }
 
@@ -556,7 +557,7 @@ mod tests {
     fn the_outer_identity_must_match_the_sealed_result_on_each_field() {
         let key = security("epiphany-distinct-test-key");
         let invocation = invocation();
-        let result = TransportResult::transported(&invocation, Vec::new(), receipt(&invocation));
+        let result = TransportResult::transported(Vec::new(), receipt(&invocation));
         let plaintext = wire_encode(&result).unwrap();
         let seal = |caller: &str, request_id: &str| {
             encrypt_message(caller, request_id, EnvelopeKind::Result, &plaintext, &key).unwrap()

crates/model-connector/src/fixtures.rs

@@ -69,6 +69,7 @@ pub(crate) fn receipt(invocation: &TransportInvocation) -> TransportReceipt {
         provider_request_sha256: invocation.provider_request_sha256,
         model: invocation.request.model.clone(),
         provider: "fixture-sse".to_string(),
+        foreign_reasoning_dropped: 0,
         outcome: TransportOutcome::Completed {
             provider_response_id: Some("response-1".to_string()),
             stop_reason: StopReason::EndTurn,
@@ -104,6 +105,7 @@ pub(crate) fn caller(
 pub(crate) fn open_service(store: &TestStore, max_concurrent_requests: usize) -> TransportService {
     TransportService::open(
         &store.path,
+        "fixture-sse",
         [
             caller(
                 "epiphany-yggdrasil",

crates/model-connector/src/serve.rs

@@ -10,12 +10,12 @@ use serde::{Deserialize, Serialize};
 use thiserror::Error;
 use zeroize::Zeroizing;
 
-use crate::contract::{TransportInvocation, TransportResult};
+use crate::contract::TransportResult;
 use crate::envelope::{
     ServiceError, TransportFrameError, decode_invocation_frame, encode_result_frame,
     frame_bytes_for_payload, read_transport_frame, write_transport_frame,
 };
-use crate::service::{CallerAdmission, TransportAdmission, TransportService};
+use crate::service::{CallerAdmission, ProviderCall, TransportAdmission, TransportService};
 
 /// The only provider seam of the connector kit. A connector binary implements
 /// it over one model provider; the kit names no provider.
@@ -24,9 +24,14 @@ pub trait ProviderBackend: Send + Sync {
     /// opens the replay store or accepts a connection; the request path does
     /// not consult it.
     fn ready(&self) -> bool;
-    /// Executes one admitted invocation. The service has already bound the
+    /// The tag of the provider this backend fronts. The service owns it from
-    /// invocation to its caller and recorded its replay claim.
+    /// `serve` on: it names the provider on every receipt and decides which
-    fn execute(&self, invocation: &TransportInvocation) -> TransportResult;
+    /// reasoning state is foreign.
+    fn provider(&self) -> &str;
+    /// Executes one admitted call. The service has already bound it to its
+    /// caller and recorded its replay claim. The call cannot show a foreign
+    /// reasoning item and builds the result's receipt itself.
+    fn execute(&self, call: &ProviderCall) -> TransportResult;
 }
 
 /// Bounds of one serve loop. The connector binary's own document owns where
@@ -157,6 +162,7 @@ pub fn serve(
     }
     let service = Arc::new(Mutex::new(TransportService::open(
         replay_store,
+        backend.provider(),
         admissions,
         limits.max_expiry_skew_ms,
     )?));
@@ -230,7 +236,7 @@ fn execute_inference_frame(
     let response = match admission {
         TransportAdmission::Reply(response) => response,
         TransportAdmission::Execute(claim) => {
-            let result = backend.execute(claim.invocation());
+            let result = backend.execute(claim.call());
             service
                 .lock()
                 .map_err(|_| ServeError::ServicePoisoned)?
@@ -328,7 +334,7 @@ mod tests {
     use crate::client::ConnectorClient;
     use crate::contract::{
         FailureKind, Refusal, TransportDisposition, TransportEvent, TransportEventPayload,
-        TransportOutcome, TransportResult,
+        TransportInvocation, TransportOutcome, TransportResult,
     };
     use crate::fixtures::{TestStore, caller, invocation_for, receipt, request};
 
@@ -360,17 +366,20 @@ mod tests {
             self.ready
         }
 
-        fn execute(&self, invocation: &TransportInvocation) -> TransportResult {
+        fn provider(&self) -> &str {
+            "fixture-sse"
+        }
+
+        fn execute(&self, call: &ProviderCall) -> TransportResult {
             self.executions.fetch_add(1, Ordering::SeqCst);
-            TransportResult::transported(
+            call.transported(
-                invocation,
                 vec![TransportEvent {
                     sequence: 0,
                     payload: TransportEventPayload::TextDelta {
                         text: "done".to_string(),
                     },
                 }],
-                receipt(invocation),
+                receipt(&fresh("sizing")).outcome,
             )
         }
     }
@@ -568,8 +577,13 @@ mod tests {
         // The wide completion goes straight through the service: serve holds
         // the replay store for as long as it runs, so a second serve cannot
         // open it while the first lives.
-        let mut service =
+        let mut service = TransportService::open(
-            TransportService::open(&store.path, vec![caller(CALLER, KEY, 4)], 300_000).unwrap();
+            &store.path,
+            "fixture-sse",
+            vec![caller(CALLER, KEY, 4)],
+            300_000,
+        )
+        .unwrap();
         let envelope =
             crate::envelope::encrypt_invocation(&invocation, &crate::fixtures::security(KEY))
                 .unwrap();
@@ -578,13 +592,8 @@ mod tests {
         else {
             panic!("a fresh request must execute");
         };
-        service
+        let wide = sized_result(claim.call(), 150_000);
-            .complete(
+        service.complete(*claim, wide, 1 << 20).unwrap();
-                *claim,
-                sized_result(&invocation, 150_000, "fixture-sse"),
-                1 << 20,
-            )
-            .unwrap();
         drop(service);
 
         let narrow = 140_000;
@@ -684,7 +693,7 @@ mod tests {
     fn the_smallest_frame_also_carries_the_failure_that_stands_in_for_a_result() {
         let long = "x".repeat(crate::envelope::MAX_IDENTITY_BYTES);
         let plaintext = crate::contract::wire_encode(&crate::service::result_size_failure(
-            &long, &long, &long, [0xff; 32], [0xff; 32],
+            &long, &long, &long, [0xff; 32], [0xff; 32], 0,
         ))
         .unwrap()
         .len();
@@ -913,19 +922,13 @@ mod tests {
     /// Answers every invocation with one text event of a chosen size.
     struct SizedBackend {
         text_len: usize,
-        transport: String,
         executions: AtomicUsize,
     }
 
     impl SizedBackend {
         fn new(text_len: usize) -> Arc<Self> {
-            Self::with_transport(text_len, "fixture-sse".to_string())
-        }
-
-        fn with_transport(text_len: usize, transport: String) -> Arc<Self> {
             Arc::new(Self {
                 text_len,
-                transport,
                 executions: AtomicUsize::new(0),
             })
         }
@@ -936,28 +939,25 @@ mod tests {
             true
         }
 
-        fn execute(&self, invocation: &TransportInvocation) -> TransportResult {
+        fn provider(&self) -> &str {
+            "fixture-sse"
+        }
+
+        fn execute(&self, call: &ProviderCall) -> TransportResult {
             self.executions.fetch_add(1, Ordering::SeqCst);
-            sized_result(invocation, self.text_len, &self.transport)
+            sized_result(call, self.text_len)
         }
     }
 
-    fn sized_result(
+    fn sized_result(call: &ProviderCall, text_len: usize) -> TransportResult {
-        invocation: &TransportInvocation,
+        call.transported(
-        text_len: usize,
-        transport: &str,
-    ) -> TransportResult {
-        let mut receipt = receipt(invocation);
-        receipt.provider = transport.to_string();
-        TransportResult::transported(
-            invocation,
             vec![TransportEvent {
                 sequence: 0,
                 payload: TransportEventPayload::TextDelta {
                     text: "y".repeat(text_len),
                 },
             }],
-            receipt,
+            receipt(&fresh("sizing")).outcome,
         )
     }
 
@@ -997,7 +997,25 @@ mod tests {
 
     /// The encoded size of a result carrying no text, for this request id.
     fn empty_result_len(request_id: &str) -> usize {
-        encoded_len(&sized_result(&fresh(request_id), 0, "fixture-sse"))
+        let store = TestStore::new();
+        let mut service = TransportService::open(
+            &store.path,
+            "fixture-sse",
+            vec![caller(CALLER, KEY, 4)],
+            300_000,
+        )
+        .unwrap();
+        let envelope = crate::envelope::encrypt_invocation(
+            &fresh(request_id),
+            &crate::fixtures::security(KEY),
+        )
+        .unwrap();
+        let TransportAdmission::Execute(claim) =
+            service.begin(&envelope, now_ms(), 1 << 20).unwrap()
+        else {
+            panic!("a fresh request must execute");
+        };
+        encoded_len(&sized_result(claim.call(), 0))
     }
 
     #[test]
@@ -1030,17 +1048,6 @@ mod tests {
         assert_eq!(executions, 1);
     }
 
-    #[test]
-    fn a_stand_in_failure_never_carries_the_backends_transport() {
-        let (first, second, executions) = call_twice(
-            SizedBackend::with_transport(FRAME, "t".repeat(FRAME)),
-            "request-transport",
-        );
-        assert!(failed_result_size(&first));
-        assert_eq!(first, second);
-        assert_eq!(executions, 1);
-    }
-
     /// The largest result plaintext whose sealed frame fits at the worst encoding.
     fn widest_guaranteed_plaintext(base: usize) -> usize {
         (base..=FRAME)
@@ -1093,7 +1100,13 @@ mod tests {
             let listener = TcpListener::bind("127.0.0.1:0").unwrap();
             let endpoint = listener.local_addr().unwrap();
             let service = Arc::new(Mutex::new(
-                TransportService::open(&store.path, vec![caller(CALLER, KEY, 4)], 300_000).unwrap(),
+                TransportService::open(
+                    &store.path,
+                    "fixture-sse",
+                    vec![caller(CALLER, KEY, 4)],
+                    300_000,
+                )
+                .unwrap(),
             ));
             let served = backend.clone();
             thread::spawn(move || {

crates/model-connector/src/service.rs

@@ -7,9 +7,9 @@ use sha2::{Digest, Sha256};
 use zeroize::Zeroizing;
 
 use crate::contract::{
-    ContractError, FailureKind, RECEIPT_SCHEMA_ID, RESULT_SCHEMA_ID, Refusal, TransportDisposition,
+    ContractError, FailureKind, InputItem, ProviderRequest, RECEIPT_SCHEMA_ID, RESULT_SCHEMA_ID,
-    TransportInvocation, TransportKey, TransportOutcome, TransportReceipt, TransportResult,
+    Refusal, TransportDisposition, TransportEvent, TransportInvocation, TransportKey,
-    canonical_invocation_bytes, require_id,
+    TransportOutcome, TransportReceipt, TransportResult, canonical_invocation_bytes, require_id,
 };
 use crate::envelope::{
     EnvelopeKind, MAX_IDENTITY_BYTES, ServiceError, TransportEnvelope, decrypt_invocation,
@@ -106,15 +106,57 @@ struct ReplayRecord {
     state: ReplayState,
 }
 
+/// What a backend is handed: the request with every foreign reasoning item
+/// already removed, and the means to answer it. The caller's own invocation is
+/// not held here at all, so no path from a call (Debug included) reaches
+/// foreign reasoning state, and a backend cannot write the identity of its
+/// receipt.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct ProviderCall {
+    request: ProviderRequest,
+    receipt: TransportReceipt,
+}
+
+impl ProviderCall {
+    /// The request as the provider may see it: foreign reasoning items absent,
+    /// every other item in the caller's order.
+    pub fn request(&self) -> &ProviderRequest {
+        &self.request
+    }
+
+    /// How many foreign reasoning items the service removed from the request.
+    pub fn foreign_reasoning_dropped(&self) -> u32 {
+        self.receipt.foreign_reasoning_dropped
+    }
+
+    /// The result of this call. The whole receipt (schema, ids, both digests,
+    /// model, provider tag and drop count) is derived here, so a backend
+    /// writes only the events and the outcome.
+    pub fn transported(
+        &self,
+        events: Vec<TransportEvent>,
+        outcome: TransportOutcome,
+    ) -> TransportResult {
+        TransportResult::transported(
+            events,
+            TransportReceipt {
+                outcome,
+                ..self.receipt.clone()
+            },
+        )
+    }
+}
+
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct ExecutionClaim {
+    call: ProviderCall,
     invocation: TransportInvocation,
     invocation_sha256: [u8; 32],
 }
 
 impl ExecutionClaim {
-    pub fn invocation(&self) -> &TransportInvocation {
+    pub fn call(&self) -> &ProviderCall {
-        &self.invocation
+        &self.call
     }
 }
 
@@ -129,15 +171,23 @@ pub struct TransportService {
     live: HashSet<RequestIdentity>,
     replay_store: CultCache,
     max_expiry_skew_ms: u64,
+    provider: String,
 }
 
 impl TransportService {
+    /// `provider` is the tag of the backend this service fronts. The service
+    /// owns it from here on: it decides which reasoning state is foreign and
+    /// what provider every receipt names.
     pub fn open(
         replay_store_path: &Path,
+        provider: &str,
         admissions: impl IntoIterator<Item = CallerAdmission>,
         max_expiry_skew_ms: u64,
     ) -> Result<Self, ServiceError> {
-        if max_expiry_skew_ms == 0 {
+        if max_expiry_skew_ms == 0
+            || require_id(provider, "provider").is_err()
+            || provider == STAND_IN_PROVIDER
+        {
             return Err(ServiceError::InvalidAdmission);
         }
         let mut callers = HashMap::new();
@@ -195,6 +245,7 @@ impl TransportService {
             live: HashSet::new(),
             replay_store,
             max_expiry_skew_ms,
+            provider: provider.to_string(),
         })
     }
 
@@ -242,6 +293,11 @@ impl TransportService {
         if invocation.request.max_output_tokens > caller.max_output_tokens {
             return self.reply_refusal(&invocation, Refusal::OutputBound, &security);
         }
+        let (request, foreign_reasoning_dropped) =
+            match partition_reasoning(&invocation.request, &self.provider) {
+                Ok(partition) => partition,
+                Err(refusal) => return self.reply_refusal(&invocation, refusal, &security),
+            };
 
         let identity = RequestIdentity {
             caller_runtime_id: invocation.caller_runtime_id.clone(),
@@ -262,7 +318,12 @@ impl TransportService {
                     if fits_frame(response, max_frame_bytes)? {
                         return Ok(TransportAdmission::Reply(response.clone()));
                     }
-                    let stand_in = self.seal_stand_in(&invocation, &security, max_frame_bytes)?;
+                    let stand_in = self.seal_stand_in(
+                        &invocation,
+                        &security,
+                        max_frame_bytes,
+                        FailureKind::ResultSize,
+                    )?;
                     self.replay_store
                         .put(
                             replay_key(&identity),
@@ -308,6 +369,24 @@ impl TransportService {
             .map_err(replay_store_error)?;
         self.live.insert(identity);
         Ok(TransportAdmission::Execute(Box::new(ExecutionClaim {
+            call: ProviderCall {
+                receipt: TransportReceipt {
+                    schema_id: RECEIPT_SCHEMA_ID.to_string(),
+                    request_id: invocation.request_id().to_string(),
+                    caller_runtime_id: invocation.caller_runtime_id.clone(),
+                    native_request_sha256: invocation.native_request_sha256,
+                    provider_request_sha256: invocation.provider_request_sha256,
+                    model: invocation.request.model.clone(),
+                    provider: self.provider.clone(),
+                    foreign_reasoning_dropped,
+                    // Replaced by the backend's outcome in `transported`.
+                    outcome: TransportOutcome::Failed {
+                        kind: FailureKind::Provider,
+                        message: String::new(),
+                    },
+                },
+                request,
+            },
             invocation,
             invocation_sha256,
         })))
@@ -324,16 +403,10 @@ impl TransportService {
         result: TransportResult,
         max_frame_bytes: usize,
     ) -> Result<TransportEnvelope, ServiceError> {
-        if !matches!(
+        let invocation = &claim.invocation;
-            &result.disposition,
-            TransportDisposition::Transported { .. }
-        ) {
-            return Err(ServiceError::InvalidCompletion);
-        }
-        result.validate_against(&claim.invocation)?;
         let identity = RequestIdentity {
-            caller_runtime_id: claim.invocation.caller_runtime_id.clone(),
+            caller_runtime_id: invocation.caller_runtime_id.clone(),
-            request_id: claim.invocation.request_id().to_string(),
+            request_id: invocation.request_id().to_string(),
         };
         if !self.live.contains(&identity) {
             return Err(ServiceError::NoActiveRequest);
@@ -353,17 +426,39 @@ impl TransportService {
             .get(&identity.caller_runtime_id)
             .ok_or(ServiceError::CallerNotAdmitted)?;
         let security = caller.security.clone();
-        let mut response = encrypt_result(&result, &security)?;
+        // A result the service refuses (not a transported result, not bound to
-        if !fits_frame(&response, max_frame_bytes)? {
+        // this invocation, or carrying a provider tag or drop count the call
-            response = match self.seal_stand_in(&claim.invocation, &security, max_frame_bytes) {
+        // did not derive) is answered like an oversized one: a typed failure
-                Ok(stand_in) => stand_in,
+        // is recorded and the slot released, so the caller gets an answer and
-                Err(error) => {
+        // a retry replays it.
-                    // Nothing is recorded, but the caller's slot is not held
+        let admissible = self.admits_result(&result, &claim);
-                    // by a request that can no longer finish.
+        let mut response = if admissible {
+            encrypt_result(&result, &security)?
+        } else {
+            self.seal_stand_in(
+                invocation,
+                &security,
+                max_frame_bytes,
+                FailureKind::Provider,
+            )
+            .inspect_err(|_| {
+                self.live.remove(&identity);
+            })?
+        };
+        if admissible && !fits_frame(&response, max_frame_bytes)? {
+            // Nothing is recorded when even the stand-in cannot be carried,
+            // but the caller's slot is not held by a request that can no
+            // longer finish.
+            response = self
+                .seal_stand_in(
+                    invocation,
+                    &security,
+                    max_frame_bytes,
+                    FailureKind::ResultSize,
+                )
+                .inspect_err(|_| {
                     self.live.remove(&identity);
-                    return Err(error);
+                })?;
-                }
-            };
         }
         let caller = self
             .callers
@@ -374,7 +469,7 @@ impl TransportService {
             request_id: identity.request_id.clone(),
             connection_key_epoch: caller.connection_key_epoch,
             invocation_sha256: claim.invocation_sha256,
-            expires_at_unix_ms: claim.invocation.expires_at_unix_ms,
+            expires_at_unix_ms: invocation.expires_at_unix_ms,
             state: ReplayState::Completed {
                 response: response.clone(),
             },
@@ -392,14 +487,20 @@ impl TransportService {
         invocation: &TransportInvocation,
         security: &TransportKey,
         max_frame_bytes: usize,
+        kind: FailureKind,
     ) -> Result<TransportEnvelope, ServiceError> {
+        let (_, foreign_reasoning_dropped) =
+            partition_reasoning(&invocation.request, &self.provider)
+                .map_err(|_| ServiceError::InvalidCompletion)?;
         let stand_in = encrypt_result(
-            &result_size_failure(
+            &stand_in_failure(
                 &invocation.caller_runtime_id,
                 invocation.request_id(),
                 &invocation.request.model,
                 invocation.native_request_sha256,
                 invocation.provider_request_sha256,
+                foreign_reasoning_dropped,
+                kind,
             ),
             security,
         )?;
@@ -410,6 +511,18 @@ impl TransportService {
         }
     }
 
+    /// Whether `result` is the answer to this claim's call: transported,
+    /// bound to the caller's invocation, and carrying the provider tag and drop
+    /// count the service derived.
+    fn admits_result(&self, result: &TransportResult, claim: &ExecutionClaim) -> bool {
+        let TransportDisposition::Transported { receipt, .. } = &result.disposition else {
+            return false;
+        };
+        result.validate_against(&claim.invocation).is_ok()
+            && receipt.provider == self.provider
+            && receipt.foreign_reasoning_dropped == claim.call.receipt.foreign_reasoning_dropped
+    }
+
     fn reply_refusal(
         &self,
         invocation: &TransportInvocation,
@@ -433,13 +546,41 @@ const STAND_IN_PROVIDER: &str = "model-connector";
 /// The failed result that stands in for one whose sealed frame cannot be
 /// carried: the same shape a provider failure takes, with nothing a provider
 /// controls but the identities the invocation already bound.
+#[cfg(test)]
 pub(crate) fn result_size_failure(
     caller_runtime_id: &str,
     request_id: &str,
     model: &str,
     native_request_sha256: [u8; 32],
     provider_request_sha256: [u8; 32],
+    foreign_reasoning_dropped: u32,
 ) -> TransportResult {
+    stand_in_failure(
+        caller_runtime_id,
+        request_id,
+        model,
+        native_request_sha256,
+        provider_request_sha256,
+        foreign_reasoning_dropped,
+        FailureKind::ResultSize,
+    )
+}
+
+/// The stand-in failure for `kind`: `ResultSize` for a result that cannot be
+/// carried, `Provider` for one the service refused.
+fn stand_in_failure(
+    caller_runtime_id: &str,
+    request_id: &str,
+    model: &str,
+    native_request_sha256: [u8; 32],
+    provider_request_sha256: [u8; 32],
+    foreign_reasoning_dropped: u32,
+    kind: FailureKind,
+) -> TransportResult {
+    let message = match kind {
+        FailureKind::ResultSize => "provider result exceeded its byte bound",
+        _ => "the service refused the backend's result",
+    };
     TransportResult {
         schema_id: RESULT_SCHEMA_ID.to_string(),
         request_id: request_id.to_string(),
@@ -454,15 +595,50 @@ pub(crate) fn result_size_failure(
                 provider_request_sha256,
                 model: model.to_string(),
                 provider: STAND_IN_PROVIDER.to_string(),
+                foreign_reasoning_dropped,
                 outcome: TransportOutcome::Failed {
-                    kind: FailureKind::ResultSize,
+                    kind,
-                    message: "provider result exceeded its byte bound".to_string(),
+                    message: message.to_string(),
                 },
             }),
         },
     }
 }
 
+/// The one place foreignness is decided. A reasoning item of another provider
+/// in the in-flight exchange (after the last user text; the whole input when
+/// there is none) is refused, because dropping it would break the provider's
+/// own tool-exchange rules. Earlier foreign items are removed and counted.
+/// Foreignness is the provider tag alone: another model of this provider
+/// passes through for the provider to judge.
+fn partition_reasoning(
+    request: &ProviderRequest,
+    provider: &str,
+) -> Result<(ProviderRequest, u32), Refusal> {
+    let in_flight_from = request
+        .input
+        .iter()
+        .rposition(|item| matches!(item, InputItem::UserText { .. }))
+        .map_or(0, |last_user_text| last_user_text + 1);
+    let mut input = Vec::with_capacity(request.input.len());
+    let mut dropped = 0u32;
+    for (position, item) in request.input.iter().enumerate() {
+        if let InputItem::ReasoningState { provider: tag, .. } = item
+            && tag != provider
+        {
+            if position >= in_flight_from {
+                return Err(Refusal::ForeignReasoningState);
+            }
+            dropped += 1;
+            continue;
+        }
+        input.push(item.clone());
+    }
+    let mut filtered = request.clone();
+    filtered.input = input;
+    Ok((filtered, dropped))
+}
+
 fn replay_key(identity: &RequestIdentity) -> String {
     let mut hasher = Sha256::new();
     hasher.update((identity.caller_runtime_id.len() as u64).to_be_bytes());
@@ -509,6 +685,7 @@ mod tests {
         assert!(matches!(
             TransportService::open(
                 &store.path,
+                "fixture-sse",
                 [
                     caller("epiphany-yggdrasil", "shared-key", 1),
                     caller("ghostlight-yggdrasil", "shared-key", 1),
@@ -566,7 +743,6 @@ mod tests {
             .complete(
                 *claim,
                 TransportResult::transported(
-                    &invocation,
                     vec![TransportEvent {
                         sequence: 0,
                         payload: TransportEventPayload::ToolCall {
@@ -710,6 +886,7 @@ mod tests {
         assert!(matches!(
             TransportService::open(
                 &store.path,
+                "fixture-sse",
                 [CallerAdmission::new(
                     "epiphany-yggdrasil",
                     "rotated-connection-key",
@@ -818,7 +995,7 @@ mod tests {
                 32_768,
             )
             .unwrap();
-            TransportService::open(&store.path, [admission], 5_000)
+            TransportService::open(&store.path, "fixture-sse", [admission], 5_000)
                 .unwrap()
                 .begin(&envelope, 1_000, FRAME)
         };
@@ -887,7 +1064,15 @@ mod tests {
     fn restart_refuses_each_malformed_replay_record() {
         let control = TestStore::new();
         seed(&control.path, &seeded_key(), |_| {});
-        assert!(TransportService::open(&control.path, [caller(CALLER, KEY, 1)], 5_000).is_ok());
+        assert!(
+            TransportService::open(
+                &control.path,
+                "fixture-sse",
+                [caller(CALLER, KEY, 1)],
+                5_000
+            )
+            .is_ok()
+        );
 
         type Edit = fn(&mut ReplayRecord);
         let cases: [(&str, Edit); 3] = [
@@ -905,7 +1090,12 @@ mod tests {
             seed(&store.path, &key, edit);
             assert!(
                 matches!(
-                    TransportService::open(&store.path, [caller(CALLER, KEY, 1)], 5_000),
+                    TransportService::open(
+                        &store.path,
+                        "fixture-sse",
+                        [caller(CALLER, KEY, 1)],
+                        5_000
+                    ),
                     Err(ServiceError::InvalidReplayRecord)
                 ),
                 "{name}"
@@ -921,16 +1111,7 @@ mod tests {
         let TransportAdmission::Execute(claim) = admission else {
             panic!("first invocation must execute");
         };
-        let result = TransportResult::transported(
+        let result = text_result(claim.call(), "done");
-            claim.invocation(),
-            vec![TransportEvent {
-                sequence: 0,
-                payload: TransportEventPayload::TextDelta {
-                    text: "done".to_string(),
-                },
-            }],
-            receipt(claim.invocation()),
-        );
 
         let mut forged = (*claim).clone();
         forged.invocation_sha256 = [1; 32];
@@ -1071,22 +1252,15 @@ mod tests {
         }
     }
 
-    fn text_result(
+    fn text_result(call: &ProviderCall, text: &str) -> TransportResult {
-        invocation: &TransportInvocation,
+        call.transported(
-        text: &str,
-        transport: &str,
-    ) -> TransportResult {
-        let mut receipt = receipt(invocation);
-        receipt.provider = transport.to_string();
-        TransportResult::transported(
-            invocation,
             vec![TransportEvent {
                 sequence: 0,
                 payload: TransportEventPayload::TextDelta {
                     text: text.to_string(),
                 },
             }],
-            receipt,
+            receipt(&invocation_for(CALLER, "outcome")).outcome,
         )
     }
 
@@ -1095,7 +1269,7 @@ mod tests {
         let store = TestStore::new();
         let mut service = open_service(&store, 8);
         let (claim, invocation) = claim_for(&mut service, "stand-in");
-        let big = text_result(&invocation, &"y".repeat(4000), &"t".repeat(5000));
+        let big = text_result(claim.call(), &"y".repeat(4000));
         let response = service.complete(*claim, big, 2000).unwrap();
         assert!(encode_result_frame(&response).unwrap().len() <= 2000);
         let stand_in = decrypt_result(&response, &security(KEY), &invocation).unwrap();
@@ -1107,6 +1281,7 @@ mod tests {
                 &invocation.request.model,
                 invocation.native_request_sha256,
                 invocation.provider_request_sha256,
+                0,
             )
         );
         let TransportDisposition::Transported { receipt, .. } = &stand_in.disposition else {
@@ -1129,7 +1304,7 @@ mod tests {
         let store = TestStore::new();
         let mut service = open_service(&store, 8);
         let (claim, invocation) = claim_for(&mut service, "fits");
-        let small = text_result(&invocation, "done", "fixture-sse");
+        let small = text_result(claim.call(), "done");
         let response = service.complete(*claim, small.clone(), 1 << 20).unwrap();
         assert_eq!(
             decrypt_result(&response, &security(KEY), &invocation).unwrap(),
@@ -1142,7 +1317,7 @@ mod tests {
         let store = TestStore::new();
         let mut service = open_service(&store, 1);
         let (claim, invocation) = claim_for(&mut service, "wedge");
-        let big = text_result(&invocation, "y", "fixture-sse");
+        let big = text_result(claim.call(), "y");
         assert_eq!(
             service.complete(*claim, big, 10).unwrap_err(),
             ServiceError::FrameBound
@@ -1169,7 +1344,7 @@ mod tests {
         let store = TestStore::new();
         let mut service = open_service(&store, 8);
         let (claim, invocation) = claim_for(&mut service, "restart");
-        let big = text_result(&invocation, &"y".repeat(4000), "fixture-sse");
+        let big = text_result(claim.call(), &"y".repeat(4000));
         let recorded = service.complete(*claim, big, FRAME).unwrap();
         assert!(encode_result_frame(&recorded).unwrap().len() > 2000);
         drop(service);
@@ -1200,6 +1375,7 @@ mod tests {
                 &invocation.request.model,
                 invocation.native_request_sha256,
                 invocation.provider_request_sha256,
+                0,
             )
         );
         // The stand-in is what is recorded now, byte for byte, at any frame.
@@ -1217,7 +1393,7 @@ mod tests {
         let store = TestStore::new();
         let mut service = open_service(&store, 8);
         let (claim, invocation) = claim_for(&mut service, "no-room");
-        let big = text_result(&invocation, "y", "fixture-sse");
+        let big = text_result(claim.call(), "y");
         service.complete(*claim, big, FRAME).unwrap();
         assert_eq!(
             service.begin(&raw_envelope(&invocation), 1_000, 10).err(),
@@ -1230,7 +1406,7 @@ mod tests {
         let store = TestStore::new();
         let mut service = open_service(&store, 8);
         let (claim, invocation) = claim_for(&mut service, "nothing-fits");
-        let big = text_result(&invocation, "y", "fixture-sse");
+        let big = text_result(claim.call(), "y");
         assert_eq!(
             service.complete(*claim, big, 10).unwrap_err(),
             ServiceError::FrameBound
@@ -1271,4 +1447,324 @@ mod tests {
             assert_eq!(contract_refusal(&other), Refusal::Malformed, "{other:?}");
         }
     }
+
+    fn user(text: &str) -> InputItem {
+        InputItem::UserText {
+            text: text.to_string(),
+        }
+    }
+
+    fn state(provider: &str, model: &str, byte: u8) -> InputItem {
+        InputItem::ReasoningState {
+            provider: provider.to_string(),
+            model: model.to_string(),
+            state: vec![byte],
+        }
+    }
+
+    fn admit_input(
+        service: &mut TransportService,
+        request_id: &str,
+        input: Vec<InputItem>,
+    ) -> (TransportAdmission, TransportInvocation) {
+        run(service, request_id, |request| request.input = input)
+    }
+
+    #[test]
+    fn foreign_reasoning_in_flight_is_refused_and_never_executed() {
+        let store = TestStore::new();
+        let mut service = open_service(&store, 1);
+        let (admission, invocation) = admit_input(
+            &mut service,
+            "in-flight",
+            vec![
+                user("question"),
+                state("fixture-sse", "gpt-5.4", 1),
+                state("other-provider", "x", 2),
+                InputItem::ToolResult {
+                    call_id: "call-1".to_string(),
+                    output: "evidence".to_string(),
+                },
+            ],
+        );
+        assert_eq!(
+            refusal_of(admission, &invocation),
+            Refusal::ForeignReasoningState
+        );
+        // Nothing was recorded or held: the caller's one slot is free and the
+        // same request id is not a replay.
+        let (admission, _) = admit_input(&mut service, "in-flight", vec![user("question")]);
+        assert!(matches!(admission, TransportAdmission::Execute(_)));
+    }
+
+    #[test]
+    fn foreign_reasoning_with_no_user_text_is_in_flight() {
+        let store = TestStore::new();
+        let mut service = open_service(&store, 4);
+        let (admission, invocation) = admit_input(
+            &mut service,
+            "no-user-text",
+            vec![
+                state("other-provider", "x", 2),
+                InputItem::AssistantText {
+                    text: "earlier".to_string(),
+                },
+            ],
+        );
+        assert_eq!(
+            refusal_of(admission, &invocation),
+            Refusal::ForeignReasoningState
+        );
+        // The boundary is the position after the last user text: a foreign item
+        // directly after it is in flight too.
+        let (admission, invocation) = admit_input(
+            &mut service,
+            "just-after",
+            vec![user("a"), state("other-provider", "x", 2)],
+        );
+        assert_eq!(
+            refusal_of(admission, &invocation),
+            Refusal::ForeignReasoningState
+        );
+    }
+
+    #[test]
+    fn foreign_reasoning_in_completed_turns_is_dropped_and_counted() {
+        let store = TestStore::new();
+        let mut service = open_service(&store, 4);
+        let own = state("fixture-sse", "gpt-5.4", 3);
+        let tool_call = InputItem::ToolCall {
+            call_id: "call-1".to_string(),
+            name: "read_source".to_string(),
+            arguments: "{}".to_string(),
+        };
+        let (admission, invocation) = admit_input(
+            &mut service,
+            "completed-turns",
+            vec![
+                state("other-provider", "x", 1),
+                user("first"),
+                own.clone(),
+                state("third-provider", "y", 2),
+                tool_call.clone(),
+                user("second"),
+                tool_call.clone(),
+                own.clone(),
+            ],
+        );
+        let TransportAdmission::Execute(claim) = admission else {
+            panic!("foreign state in completed turns must not stop the request");
+        };
+        assert_eq!(
+            claim.call().request().input,
+            vec![
+                user("first"),
+                own.clone(),
+                tool_call.clone(),
+                user("second"),
+                tool_call,
+                own,
+            ]
+        );
+        assert_eq!(claim.call().foreign_reasoning_dropped(), 2);
+        // The caller's digest binds what the caller sent, not the filtered view,
+        // and the completion below is accepted against it.
+        assert_ne!(
+            invocation.provider_request_sha256,
+            provider_request_sha256(claim.call().request()).unwrap()
+        );
+        let result = text_result(claim.call(), "done");
+        let response = service.complete(*claim, result, FRAME).unwrap();
+        let TransportDisposition::Transported { receipt, .. } =
+            decrypt_result(&response, &security(KEY), &invocation)
+                .unwrap()
+                .disposition
+        else {
+            panic!("completed");
+        };
+        assert_eq!(receipt.foreign_reasoning_dropped, 2);
+    }
+
+    #[test]
+    fn same_provider_other_model_reasoning_passes_through() {
+        let store = TestStore::new();
+        let mut service = open_service(&store, 4);
+        let other_model = state("fixture-sse", "some-other-model", 9);
+        let (admission, _) = admit_input(
+            &mut service,
+            "other-model",
+            vec![other_model.clone(), user("first"), other_model.clone()],
+        );
+        let TransportAdmission::Execute(claim) = admission else {
+            panic!("an own-provider item is never foreign");
+        };
+        assert_eq!(
+            claim.call().request().input,
+            vec![other_model.clone(), user("first"), other_model]
+        );
+        assert_eq!(claim.call().foreign_reasoning_dropped(), 0);
+    }
+
+    #[test]
+    fn open_refuses_a_blank_or_stand_in_provider_tag() {
+        let store = TestStore::new();
+        for tag in ["", " ", STAND_IN_PROVIDER] {
+            assert!(
+                matches!(
+                    TransportService::open(&store.path, tag, [caller(CALLER, KEY, 1)], 5_000),
+                    Err(ServiceError::InvalidAdmission)
+                ),
+                "{tag:?}"
+            );
+        }
+        assert!(
+            TransportService::open(&store.path, "fixture-sse", [caller(CALLER, KEY, 1)], 5_000)
+                .is_ok()
+        );
+    }
+
+    #[test]
+    fn complete_answers_a_hand_built_receipt_with_another_provider_or_count_as_a_typed_failure() {
+        let store = TestStore::new();
+        let mut service = open_service(&store, 1);
+        let input = vec![state("other-provider", "x", 1), user("first")];
+        let tamper_edits: [fn(&mut TransportReceipt); 4] = [
+            |receipt| receipt.provider = "other-provider".to_string(),
+            |receipt| receipt.provider = STAND_IN_PROVIDER.to_string(),
+            |receipt| receipt.foreign_reasoning_dropped = 2,
+            |receipt| receipt.foreign_reasoning_dropped = 0,
+        ];
+        for (index, edit) in tamper_edits.into_iter().enumerate() {
+            let id = format!("hand-built-{index}");
+            let (admission, invocation) = admit_input(&mut service, &id, input.clone());
+            let TransportAdmission::Execute(claim) = admission else {
+                panic!("a refused completion must have released the slot");
+            };
+            assert_eq!(claim.call().foreign_reasoning_dropped(), 1);
+            let mut bad = text_result(claim.call(), "done");
+            let TransportDisposition::Transported { receipt, .. } = &mut bad.disposition else {
+                unreachable!();
+            };
+            edit(receipt);
+            let response = service.complete(*claim, bad, FRAME).unwrap();
+            let answer = decrypt_result(&response, &security(KEY), &invocation).unwrap();
+            let TransportDisposition::Transported { events, receipt } = &answer.disposition else {
+                panic!("a typed failure is transported");
+            };
+            assert!(events.is_empty());
+            assert_eq!(receipt.provider, STAND_IN_PROVIDER);
+            assert_eq!(receipt.foreign_reasoning_dropped, 1);
+            assert!(matches!(
+                receipt.outcome,
+                TransportOutcome::Failed {
+                    kind: FailureKind::Provider,
+                    ..
+                }
+            ));
+            // A retry of the same id replays the failure, not ReplayConflict.
+            let TransportAdmission::Reply(replay) = service
+                .begin(&raw_envelope(&invocation), 1_000, FRAME)
+                .unwrap()
+            else {
+                panic!("a retry must replay the recorded failure");
+            };
+            assert_eq!(replay, response);
+        }
+    }
+
+    #[test]
+    fn a_result_that_fails_validation_is_answered_as_a_typed_failure_and_releases_the_slot() {
+        let store = TestStore::new();
+        let mut service = open_service(&store, 1);
+        let (claim, invocation) = claim_for(&mut service, "invalid-result");
+        let mut bad = text_result(claim.call(), "done");
+        bad.request_id = "someone-elses".to_string();
+        let response = service.complete(*claim, bad, FRAME).unwrap();
+        let answer = decrypt_result(&response, &security(KEY), &invocation).unwrap();
+        let TransportDisposition::Transported { receipt, .. } = &answer.disposition else {
+            panic!("a typed failure is transported");
+        };
+        assert!(matches!(
+            receipt.outcome,
+            TransportOutcome::Failed {
+                kind: FailureKind::Provider,
+                ..
+            }
+        ));
+        // The caller's only slot is free for the next request.
+        let (next, _) = claim_for(&mut service, "next");
+        drop(next);
+    }
+
+    #[test]
+    fn a_provider_call_formats_without_foreign_reasoning_state() {
+        let store = TestStore::new();
+        let mut service = open_service(&store, 1);
+        let canary = "canary-foreign-provider-tag";
+        let foreign = InputItem::ReasoningState {
+            provider: canary.to_string(),
+            model: canary.to_string(),
+            state: vec![0xC7, 0xC8, 0xC9, 0xCA],
+        };
+        let (admission, _) = admit_input(&mut service, "debug-leak", vec![foreign, user("first")]);
+        let TransportAdmission::Execute(claim) = admission else {
+            panic!("expected an execution claim");
+        };
+        assert_eq!(claim.call().foreign_reasoning_dropped(), 1);
+        for text in [
+            format!("{:?}", claim.call()),
+            format!("{:#?}", claim.call()),
+        ] {
+            assert!(!text.contains(canary), "{text}");
+            assert!(!text.contains("199, 200, 201, 202"), "{text}");
+        }
+    }
+
+    #[test]
+    fn stand_in_carries_the_drop_count() {
+        let store = TestStore::new();
+        let mut service = open_service(&store, 4);
+        let input = vec![state("other-provider", "x", 1), user("first")];
+        let (admission, invocation) = admit_input(&mut service, "stand-in-count", input.clone());
+        let TransportAdmission::Execute(claim) = admission else {
+            panic!("expected an execution claim");
+        };
+        let big = text_result(claim.call(), &"y".repeat(4000));
+        let response = service.complete(*claim, big, 2000).unwrap();
+        let expected = result_size_failure(
+            CALLER,
+            "stand-in-count",
+            &invocation.request.model,
+            invocation.native_request_sha256,
+            invocation.provider_request_sha256,
+            1,
+        );
+        assert_eq!(
+            decrypt_result(&response, &security(KEY), &invocation).unwrap(),
+            expected
+        );
+
+        // A recorded wide result replayed at a smaller frame keeps the count too.
+        let (admission, invocation) = admit_input(&mut service, "replay-count", input);
+        let TransportAdmission::Execute(claim) = admission else {
+            panic!("expected an execution claim");
+        };
+        let big = text_result(claim.call(), &"y".repeat(4000));
+        service.complete(*claim, big, FRAME).unwrap();
+        let TransportAdmission::Reply(smaller) = service
+            .begin(&raw_envelope(&invocation), 1_000, 2000)
+            .unwrap()
+        else {
+            panic!("expected a replay");
+        };
+        let TransportDisposition::Transported { receipt, .. } =
+            decrypt_result(&smaller, &security(KEY), &invocation)
+                .unwrap()
+                .disposition
+        else {
+            panic!("expected the stand-in");
+        };
+        assert_eq!(receipt.provider, STAND_IN_PROVIDER);
+        assert_eq!(receipt.foreign_reasoning_dropped, 1);
+    }
 }

crates/model-connector/tests/fixtures/wire_v3/README.md

@@ -5,7 +5,8 @@ produced by the kit at the revision that added them. They pin drift; the types i
 `src/contract.rs` own the shape, and `schemas/` publishes it.
 
 - `provider_request.mp`, `transport_invocation.mp`, `transport_result_transported.mp`,
-  `transport_result_refused.mp`, `transport_receipt_failed.mp`, `transport_envelope.mp`:
+  `transport_result_refused.mp`, `transport_receipt_failed.mp`, `transport_envelope.mp`,
+  `input_reasoning_state.mp` (an `InputItem::ReasoningState`, its state as MessagePack `bin`):
   the plaintext documents.
 - `carriage_invocation.frame`: a `cultnet.operation_request.v0` for service
   `gamecult.model.connector`, operation `invoke`, whose payload is the base64 of an envelope

crates/model-connector/tests/fixtures/wire_v3/input_reasoning_state.mp

@@ -0,0 +1 @@
+<EFBFBD>ReasoningState<EFBFBD>provider淮nthropic-messages叮odel畚laude-opus-4-5叫tate<74><65><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>﹜ㄓ它夾帚型陋秣捲陷絮溢劃遞蝨螃謝藥齪ヌ圴佮迓玿旂衲欶趹欹詘棰葮摵蜠樉賥濋錎膼瀔嚦黀蘜蠲╭帉爎<E5B889>

crates/model-connector/tests/published_schemas.rs

@@ -98,3 +98,18 @@ fn the_published_ciphertext_is_what_the_wire_sends() {
         .unwrap();
     assert!(matches!(wire, rmpv::Value::Binary(bytes) if bytes.len() == 40));
 }
+
+#[test]
+fn the_refusal_schema_is_one_flat_string_enum() {
+    let schema: serde_json::Value = serde_json::from_str(&render::<Refusal>()).unwrap();
+    assert!(schema.get("oneOf").is_none(), "{schema}");
+    assert_eq!(schema["type"], "string");
+    let variants: Vec<&str> = schema["enum"]
+        .as_array()
+        .expect("a closed set of strings")
+        .iter()
+        .map(|value| value.as_str().unwrap())
+        .collect();
+    assert_eq!(variants.len(), 12);
+    assert!(variants.contains(&"ForeignReasoningState"));
+}

crates/model-connector/tests/reasoning_state.rs

@@ -0,0 +1,348 @@
+//! The reasoning-state rules through a live serve loop and the public surface
+//! only: what a backend is shown, what a caller gets back and what it replays.
+#![cfg(feature = "daemon")]
+
+use std::net::TcpListener;
+use std::path::PathBuf;
+use std::sync::atomic::{AtomicUsize, Ordering};
+use std::sync::{Arc, Mutex};
+use std::thread;
+use std::time::{Duration, SystemTime, UNIX_EPOCH};
+
+use model_connector::*;
+
+const CALLER: &str = "reasoning-caller";
+const KEY: &str = "reasoning-distinct-test-key";
+const PROVIDER: &str = "anthropic-messages";
+const FRAME: usize = 256 * 1024;
+
+/// Answers every call with fixed events and records what it was shown.
+struct RecordingBackend {
+    events: Vec<TransportEventPayload>,
+    executions: AtomicUsize,
+    seen: Mutex<Vec<ProviderRequest>>,
+}
+
+impl RecordingBackend {
+    fn new(events: Vec<TransportEventPayload>) -> Arc<Self> {
+        Arc::new(Self {
+            events,
+            executions: AtomicUsize::new(0),
+            seen: Mutex::new(Vec::new()),
+        })
+    }
+
+    fn seen(&self) -> Vec<ProviderRequest> {
+        self.seen.lock().unwrap().clone()
+    }
+}
+
+impl ProviderBackend for RecordingBackend {
+    fn ready(&self) -> bool {
+        true
+    }
+
+    fn provider(&self) -> &str {
+        PROVIDER
+    }
+
+    fn execute(&self, call: &ProviderCall) -> TransportResult {
+        self.executions.fetch_add(1, Ordering::SeqCst);
+        self.seen.lock().unwrap().push(call.request().clone());
+        call.transported(
+            self.events
+                .iter()
+                .cloned()
+                .enumerate()
+                .map(|(sequence, payload)| TransportEvent {
+                    sequence: sequence as u64,
+                    payload,
+                })
+                .collect(),
+            TransportOutcome::Completed {
+                provider_response_id: Some("msg-1".to_string()),
+                stop_reason: StopReason::ToolUse,
+                usage: Usage {
+                    input_tokens: 1,
+                    cache_read_tokens: 0,
+                    cache_write_tokens: 0,
+                    output_tokens: 1,
+                    reasoning_tokens: None,
+                },
+            },
+        )
+    }
+}
+
+fn now_ms() -> u64 {
+    SystemTime::now()
+        .duration_since(UNIX_EPOCH)
+        .unwrap()
+        .as_millis() as u64
+}
+
+/// A running serve loop and a client for it.
+fn start(backend: Arc<RecordingBackend>) -> ConnectorClient {
+    start_with(backend, 4)
+}
+
+/// As `start`, with the caller's concurrent-request limit.
+fn start_with(backend: Arc<dyn ProviderBackend>, max_concurrent: usize) -> ConnectorClient {
+    static SEQUENCE: AtomicUsize = AtomicUsize::new(0);
+    let root: PathBuf = std::env::temp_dir().join(format!(
+        "model-connector-reasoning-{}-{}",
+        std::process::id(),
+        SEQUENCE.fetch_add(1, Ordering::Relaxed)
+    ));
+    std::fs::create_dir_all(&root).unwrap();
+    let store = root.join("replay.cc");
+    let listener = TcpListener::bind("127.0.0.1:0").unwrap();
+    let endpoint = listener.local_addr().unwrap();
+    let admission = CallerAdmission::new(
+        CALLER,
+        KEY,
+        1,
+        ["claude-opus-4-5".to_string()],
+        max_concurrent,
+        64 * 1024,
+        32_768,
+    )
+    .unwrap();
+    let limits = ServeLimits {
+        max_frame_bytes: FRAME,
+        max_connections: 8,
+        socket_timeout_ms: 5_000,
+        max_expiry_skew_ms: 300_000,
+    };
+    thread::spawn(move || serve(listener, limits, vec![admission], &store, backend));
+    ConnectorClient::new(endpoint, KEY, FRAME, Some(Duration::from_secs(5))).unwrap()
+}
+
+fn invocation(request_id: &str, input: Vec<InputItem>) -> TransportInvocation {
+    let mut request = ProviderRequest::new(
+        request_id,
+        "conversation-1",
+        "claude-opus-4-5",
+        "Return the typed result.",
+        4_096,
+    );
+    request.input = input;
+    TransportInvocation::new(CALLER, now_ms() + 60_000, [7; 32], request).unwrap()
+}
+
+fn user(text: &str) -> InputItem {
+    InputItem::UserText {
+        text: text.to_string(),
+    }
+}
+
+fn state(provider: &str, byte: u8) -> InputItem {
+    InputItem::ReasoningState {
+        provider: provider.to_string(),
+        model: "claude-opus-4-5".to_string(),
+        state: vec![0x80 | byte, byte],
+    }
+}
+
+fn receipt_of(result: &TransportResult) -> &TransportReceipt {
+    let TransportDisposition::Transported { receipt, .. } = &result.disposition else {
+        panic!(
+            "expected a transported result, got {:?}",
+            result.disposition
+        );
+    };
+    receipt
+}
+
+#[test]
+fn foreign_reasoning_in_flight_is_refused_and_never_executed() {
+    let backend = RecordingBackend::new(vec![TransportEventPayload::TextDelta {
+        text: "done".to_string(),
+    }]);
+    let client = start(backend.clone());
+    let result = client
+        .execute(&invocation(
+            "foreign-in-flight",
+            vec![
+                user("question"),
+                InputItem::ToolCall {
+                    call_id: "call-1".to_string(),
+                    name: "read_source".to_string(),
+                    arguments: "{}".to_string(),
+                },
+                state("another-provider", 1),
+                InputItem::ToolResult {
+                    call_id: "call-1".to_string(),
+                    output: "evidence".to_string(),
+                },
+            ],
+        ))
+        .unwrap();
+    assert_eq!(
+        result.disposition,
+        TransportDisposition::Refused(Refusal::ForeignReasoningState)
+    );
+    assert_eq!(backend.executions.load(Ordering::SeqCst), 0);
+}
+
+#[test]
+fn a_backend_never_sees_foreign_reasoning_state() {
+    let backend = RecordingBackend::new(vec![TransportEventPayload::TextDelta {
+        text: "done".to_string(),
+    }]);
+    let client = start(backend.clone());
+    let own = state(PROVIDER, 2);
+    let result = client
+        .execute(&invocation(
+            "foreign-earlier",
+            vec![
+                state("another-provider", 1),
+                user("first"),
+                own.clone(),
+                state("a-third-provider", 3),
+                user("second"),
+            ],
+        ))
+        .unwrap();
+    assert_eq!(receipt_of(&result).foreign_reasoning_dropped, 2);
+    assert_eq!(receipt_of(&result).provider, PROVIDER);
+    assert_eq!(
+        backend.seen()[0].input,
+        vec![user("first"), own, user("second")]
+    );
+}
+
+#[test]
+fn replayed_transcript_reaches_the_same_provider_verbatim() {
+    let thinking = vec![0x80, 0xfe, 0x00, 0xff];
+    let backend = RecordingBackend::new(vec![
+        TransportEventPayload::TextDelta {
+            text: "let me ".to_string(),
+        },
+        TransportEventPayload::TextDelta {
+            text: "look".to_string(),
+        },
+        TransportEventPayload::ReasoningState {
+            state: thinking.clone(),
+        },
+        TransportEventPayload::ToolCall {
+            call_id: "call-1".to_string(),
+            name: "read_source".to_string(),
+            arguments: "{}".to_string(),
+        },
+    ]);
+    let client = start(backend.clone());
+    let first = client
+        .execute(&invocation("turn-1", vec![user("question")]))
+        .unwrap();
+    let added = first.transcript_items();
+    assert_eq!(
+        added,
+        vec![
+            InputItem::AssistantText {
+                text: "let me look".to_string()
+            },
+            InputItem::ReasoningState {
+                provider: PROVIDER.to_string(),
+                model: "claude-opus-4-5".to_string(),
+                state: thinking,
+            },
+            InputItem::ToolCall {
+                call_id: "call-1".to_string(),
+                name: "read_source".to_string(),
+                arguments: "{}".to_string(),
+            },
+        ]
+    );
+
+    // The caller appends the items untouched and answers the tool call; the
+    // next call is in flight on the same provider and is admitted as it is.
+    let mut next = vec![user("question")];
+    next.extend(added.clone());
+    next.push(InputItem::ToolResult {
+        call_id: "call-1".to_string(),
+        output: "evidence".to_string(),
+    });
+    let second = client.execute(&invocation("turn-2", next.clone())).unwrap();
+    assert_eq!(receipt_of(&second).foreign_reasoning_dropped, 0);
+    assert_eq!(backend.seen()[1].input, next);
+}
+
+/// A backend that answers with a receipt it has edited after the service
+/// derived it.
+struct TamperingBackend {
+    edit: fn(&mut TransportReceipt),
+}
+
+impl ProviderBackend for TamperingBackend {
+    fn ready(&self) -> bool {
+        true
+    }
+
+    fn provider(&self) -> &str {
+        PROVIDER
+    }
+
+    fn execute(&self, call: &ProviderCall) -> TransportResult {
+        let mut result = call.transported(
+            vec![TransportEvent {
+                sequence: 0,
+                payload: TransportEventPayload::TextDelta {
+                    text: "done".to_string(),
+                },
+            }],
+            TransportOutcome::Completed {
+                provider_response_id: None,
+                stop_reason: StopReason::EndTurn,
+                usage: Usage {
+                    input_tokens: 1,
+                    cache_read_tokens: 0,
+                    cache_write_tokens: 0,
+                    output_tokens: 1,
+                    reasoning_tokens: None,
+                },
+            },
+        );
+        let TransportDisposition::Transported { receipt, .. } = &mut result.disposition else {
+            unreachable!();
+        };
+        (self.edit)(receipt);
+        result
+    }
+}
+
+#[test]
+fn a_refused_completion_reaches_the_caller_as_a_typed_failure_and_frees_the_slot() {
+    let edits: [fn(&mut TransportReceipt); 2] = [
+        |receipt| receipt.provider = "another-provider".to_string(),
+        |receipt| receipt.foreign_reasoning_dropped += 1,
+    ];
+    for edit in edits {
+        // One concurrent request: a wedged slot would refuse the next id.
+        let client = start_with(Arc::new(TamperingBackend { edit }), 1);
+        let first = invocation("tampered", vec![user("question")]);
+        let answer = client.execute(&first).unwrap();
+        let TransportDisposition::Transported { events, receipt } = &answer.disposition else {
+            panic!("expected a typed failure, got {:?}", answer.disposition);
+        };
+        assert!(events.is_empty());
+        assert!(matches!(
+            receipt.outcome,
+            TransportOutcome::Failed {
+                kind: FailureKind::Provider,
+                ..
+            }
+        ));
+        // The same id replays that failure rather than conflicting.
+        assert_eq!(client.execute(&first).unwrap(), answer);
+        // The next id is not refused for capacity.
+        let next = client
+            .execute(&invocation("tampered-next", vec![user("again")]))
+            .unwrap();
+        assert!(
+            !matches!(next.disposition, TransportDisposition::Refused(_)),
+            "{:?}",
+            next.disposition
+        );
+    }
+}

crates/model-connector/tests/wire_golden_v3.rs

@@ -94,6 +94,7 @@ fn receipt(outcome: TransportOutcome) -> TransportReceipt {
         provider_request_sha256: invocation.provider_request_sha256,
         model: invocation.request.model.clone(),
         provider: "anthropic-messages".to_string(),
+        foreign_reasoning_dropped: 2,
         outcome,
     }
 }
@@ -118,26 +119,46 @@ fn wire_golden_v3() {
     assert_wire("provider_request.mp", &invocation.request);
     assert_wire("transport_invocation.mp", &invocation);
 
-    let transported = TransportResult::transported(
+    // The reasoning bytes are all >= 0x80 so a byte-array encoding cannot pass
-        &invocation,
+    // for MessagePack bin.
-        vec![
+    let reasoning = || (0x80..=0xff_u8).collect::<Vec<u8>>();
-            TransportEvent {
+    assert_wire(
-                sequence: 0,
+        "input_reasoning_state.mp",
-                payload: TransportEventPayload::TextDelta {
+        &InputItem::ReasoningState {
-                    text: "thinking".to_string(),
+            provider: "anthropic-messages".to_string(),
-                },
+            model: "claude-opus-4-5".to_string(),
-            },
+            state: reasoning(),
-            TransportEvent {
+        },
-                sequence: 1,
-                payload: TransportEventPayload::ToolCall {
-                    call_id: "call-2".to_string(),
-                    name: "read_source".to_string(),
-                    arguments: "{}".to_string(),
-                },
-            },
-        ],
-        receipt(completed()),
     );
+
+    let transported = TransportResult {
+        schema_id: RESULT_SCHEMA_ID.to_string(),
+        request_id: invocation.request_id().to_string(),
+        caller_runtime_id: CALLER.to_string(),
+        disposition: TransportDisposition::Transported {
+            events: vec![
+                TransportEvent {
+                    sequence: 0,
+                    payload: TransportEventPayload::TextDelta {
+                        text: "thinking".to_string(),
+                    },
+                },
+                TransportEvent {
+                    sequence: 1,
+                    payload: TransportEventPayload::ReasoningState { state: reasoning() },
+                },
+                TransportEvent {
+                    sequence: 2,
+                    payload: TransportEventPayload::ToolCall {
+                        call_id: "call-2".to_string(),
+                        name: "read_source".to_string(),
+                        arguments: "{}".to_string(),
+                    },
+                },
+            ],
+            receipt: Box::new(receipt(completed())),
+        },
+    };
     assert_eq!(transported.validate_against(&invocation), Ok(()));
     assert_wire("transport_result_transported.mp", &transported);
 
@@ -212,3 +233,12 @@ fn the_golden_carriage_frame_decrypts_and_validates_under_the_fixed_key() {
     assert_eq!(decrypted, invocation);
     assert_eq!(decrypted.validate(1_799_999_999_000, 5_000), Ok(()));
 }
+
+/// The reasoning bytes travel as MessagePack `bin` (0xc4 length marker), never
+/// as an array of integers.
+#[test]
+fn reasoning_state_is_messagepack_bin() {
+    let golden = std::fs::read(fixtures().join("input_reasoning_state.mp")).unwrap();
+    let marker = golden.windows(3).any(|window| window == [0xc4, 0x80, 0x80]);
+    assert!(marker, "state must be a bin 8 of 128 bytes starting 0x80");
+}

schemas/provider_request.json

@@ -186,6 +186,38 @@
           "required": [
             "ToolResult"
           ]
+        },
+        {
+          "description": "One provider reasoning block, opaque to every caller: `state` is the\nconnector's own encoding of the whole block. Callers replay it\nverbatim in transcript order and never inspect or branch on it; only\nthe connector of `provider` reads it, and the service drops or refuses\nthe state of any other provider before a backend sees the request.",
+          "type": "object",
+          "properties": {
+            "ReasoningState": {
+              "type": "object",
+              "properties": {
+                "model": {
+                  "type": "string"
+                },
+                "provider": {
+                  "type": "string"
+                },
+                "state": {
+                  "description": "MessagePack bin: raw bytes, never an array of integers",
+                  "type": "string",
+                  "format": "binary"
+                }
+              },
+              "additionalProperties": false,
+              "required": [
+                "provider",
+                "model",
+                "state"
+              ]
+            }
+          },
+          "additionalProperties": false,
+          "required": [
+            "ReasoningState"
+          ]
         }
       ]
     },

schemas/transport_envelope.json

@@ -7,7 +7,7 @@
       "type": "string"
     },
     "ciphertext": {
-      "description": "MessagePack bin: the raw ciphertext bytes, never an array of integers",
+      "description": "MessagePack bin: raw bytes, never an array of integers",
       "type": "string",
       "format": "binary"
     },

schemas/transport_invocation.json

@@ -154,6 +154,38 @@
           "required": [
             "ToolResult"
           ]
+        },
+        {
+          "description": "One provider reasoning block, opaque to every caller: `state` is the\nconnector's own encoding of the whole block. Callers replay it\nverbatim in transcript order and never inspect or branch on it; only\nthe connector of `provider` reads it, and the service drops or refuses\nthe state of any other provider before a backend sees the request.",
+          "type": "object",
+          "properties": {
+            "ReasoningState": {
+              "type": "object",
+              "properties": {
+                "model": {
+                  "type": "string"
+                },
+                "provider": {
+                  "type": "string"
+                },
+                "state": {
+                  "description": "MessagePack bin: raw bytes, never an array of integers",
+                  "type": "string",
+                  "format": "binary"
+                }
+              },
+              "additionalProperties": false,
+              "required": [
+                "provider",
+                "model",
+                "state"
+              ]
+            }
+          },
+          "additionalProperties": false,
+          "required": [
+            "ReasoningState"
+          ]
         }
       ]
     },

schemas/transport_receipt.json

@@ -6,6 +6,12 @@
     "caller_runtime_id": {
       "type": "string"
     },
+    "foreign_reasoning_dropped": {
+      "description": "How many foreign `ReasoningState` items the service removed from the\nrequest before the backend saw it.",
+      "type": "integer",
+      "format": "uint32",
+      "minimum": 0
+    },
     "model": {
       "type": "string"
     },
@@ -53,6 +59,7 @@
     "provider_request_sha256",
     "model",
     "provider",
+    "foreign_reasoning_dropped",
     "outcome"
   ],
   "$defs": {

schemas/transport_result.json

@@ -50,7 +50,8 @@
         "InFlight",
         "Indeterminate",
         "ReplayConflict",
-        "Malformed"
+        "Malformed",
+        "ForeignReasoningState"
       ]
     },
     "StopReason": {
@@ -178,6 +179,30 @@
           "required": [
             "ToolCall"
           ]
+        },
+        {
+          "description": "One reasoning block of the provider that answered. It carries no\nprovider or model: the receipt names them, so a backend cannot tag its\nown state.",
+          "type": "object",
+          "properties": {
+            "ReasoningState": {
+              "type": "object",
+              "properties": {
+                "state": {
+                  "description": "MessagePack bin: raw bytes, never an array of integers",
+                  "type": "string",
+                  "format": "binary"
+                }
+              },
+              "additionalProperties": false,
+              "required": [
+                "state"
+              ]
+            }
+          },
+          "additionalProperties": false,
+          "required": [
+            "ReasoningState"
+          ]
         }
       ]
     },
@@ -247,6 +272,12 @@
         "caller_runtime_id": {
           "type": "string"
         },
+        "foreign_reasoning_dropped": {
+          "description": "How many foreign `ReasoningState` items the service removed from the\nrequest before the backend saw it.",
+          "type": "integer",
+          "format": "uint32",
+          "minimum": 0
+        },
         "model": {
           "type": "string"
         },
@@ -294,6 +325,7 @@
         "provider_request_sha256",
         "model",
         "provider",
+        "foreign_reasoning_dropped",
         "outcome"
       ]
     },