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Merged
Tryanks merged 1 commit into from
Sep 18, 2026
Merged

Stop Claude Code turns whenever the serving model changes #458

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258 changes: 156 additions & 102 deletions crates/agent/src/claude.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1159,11 +1159,12 @@ struct PendingRewind {
conversation: bool,
}

fn served_model_is_fallback(expected: &str, served: &str) -> bool {
(expected.contains("fable") && served.contains("opus"))
|| (served.contains("opus-4-8")
&& expected.contains("opus")
&& !expected.contains("opus-4-8"))
fn served_model_changed(expected: &str, served: &str) -> bool {
// CLI-generated errors/refusals do not identify a serving model.
!served.is_empty()
&& served != "<synthetic>"
&& !strip_context_window_suffix(expected)
.eq_ignore_ascii_case(strip_context_window_suffix(served))
}

pub(crate) struct Mapper {
Expand Down Expand Up @@ -1243,7 +1244,7 @@ pub(crate) struct Mapper {
native_rewind: bool,
/// Last assistant model published to the canonical event stream.
last_served_model: Option<String>,
/// Model selected for this session, used when Claude reports a synthetic refusal message.
/// Selected model: the comparison baseline and the source for synthetic refusals.
expected_model: Option<String>,
/// Whether a served-model mismatch was already reported for the active turn.
fallback_detected: bool,
Expand Down Expand Up @@ -1693,6 +1694,9 @@ impl Mapper {
log::debug!("claude: ignoring malformed model_refusal_fallback");
return Vec::new();
};
if !served_model_changed(expected, actual) {
return Vec::new();
}
self.fallback_detected = true;
vec![AgentEvent::ModelFallbackDetected {
expected: expected.to_owned(),
Expand Down Expand Up @@ -1996,11 +2000,13 @@ impl Mapper {
.and_then(Value::as_str)
.map(str::to_string);
let message = &event["message"];
self.observe_request_usage(
let mut events = self.observe_served_model(message);
events.extend(self.observe_request_usage(
message.get("id").and_then(Value::as_str),
message.get("usage"),
true,
)
));
events
}
Some("content_block_delta") => {
let index = event.get("index").and_then(Value::as_u64).unwrap_or(0);
Expand Down Expand Up @@ -2118,6 +2124,39 @@ impl Mapper {
}
}

fn observe_served_model(&mut self, message: &Value) -> Vec<AgentEvent> {
let Some(model) = message
.get("model")
.and_then(Value::as_str)
.filter(|model| !model.is_empty() && *model != "<synthetic>")
else {
return Vec::new();
};
let mut events = Vec::new();
if !self.fallback_detected
&& let Some(expected) = self.expected_model.as_deref()
&& served_model_changed(expected, model)
{
self.fallback_detected = true;
events.push(AgentEvent::ModelFallbackDetected {
expected: expected.to_owned(),
actual: model.to_owned(),
category: None,
checkpoint_id: None,
// Child messages are routed to their own mapper by on_message.
parent_tool_use_id: None,
});
}
if self.last_served_model.as_deref() != Some(model) {
self.last_served_model = Some(model.to_owned());
events.push(AgentEvent::ServedModel {
model: model.to_owned(),
reason: None,
});
}
events
}

fn on_assistant(&mut self, msg: &Value) -> Vec<AgentEvent> {
let message = match msg.get("message") {
Some(m) => m,
Expand All @@ -2138,42 +2177,7 @@ impl Mapper {
.and_then(Value::as_str)
.map(ClassifierCategory::parse);
}
if let Some(model) = message.get("model").and_then(Value::as_str) {
if !self.fallback_detected
&& let Some(expected) = self.expected_model.as_deref()
{
let normalized_expected = expected
.split('[')
.next()
.unwrap_or(expected)
.to_ascii_lowercase();
let normalized_served = model
.split('[')
.next()
.unwrap_or(model)
.to_ascii_lowercase();
if served_model_is_fallback(&normalized_expected, &normalized_served) {
self.fallback_detected = true;
out.push(AgentEvent::ModelFallbackDetected {
expected: expected.to_owned(),
actual: model.to_owned(),
category: None,
checkpoint_id: None,
parent_tool_use_id: msg
.get("parent_tool_use_id")
.and_then(Value::as_str)
.map(str::to_owned),
});
}
}
if self.last_served_model.as_deref() != Some(model) {
self.last_served_model = Some(model.to_owned());
out.push(AgentEvent::ServedModel {
model: model.to_owned(),
reason: None,
});
}
}
out.extend(self.observe_served_model(message));
out.extend(self.observe_stop_reason(message.get("stop_reason").and_then(Value::as_str)));
let msg_id = message
.get("id")
Expand Down Expand Up @@ -3396,78 +3400,128 @@ mod tests {
}

#[test]
fn served_model_fallback_family_rule() {
let cases = [
("claude-fable-5", "claude-opus-4-8", true),
("claude-fable-5", "claude-opus-5", true),
("claude-opus-5", "claude-opus-4-8", true),
("claude-opus-4-8", "claude-opus-4-8", false),
("claude-fable-5", "claude-fable-5", false),
("claude-fable-5", "claude-sonnet-4-5", false),
("claude-fable-5", "claude-haiku-4-5", false),
("anything", "<synthetic>", false),
];
for (expected, served, is_fallback) in cases {
fn assistant_model_changes_are_detected_without_family_rules() {
for (expected, served, changed) in [
("claude-fable-5-1", "claude-fable-5", true),
("claude-fable-5-1", "claude-opus-5", true),
("claude-fable-5-1", "claude-opus-4-8", true),
("claude-fable-5-1", "claude-sonnet-4-5", true),
("claude-fable-5-1", "claude-haiku-4-5", true),
("claude-opus-4-8", "claude-opus-5", true),
("custom-model", "another-model", true),
("claude-fable-5-1", "claude-fable-5-1", false),
("claude-opus-5[1m]", "claude-opus-5", false),
("claude-opus-5", "CLAUDE-OPUS-5[1M]", false),
("claude-opus-5[2m]", "claude-opus-5", false),
("custom-model[variant]", "custom-model", true),
("claude-fable-5-1", "<synthetic>", false),
] {
let mut mapper = Mapper::new_configured(
false,
InteractionMode::Build,
"default",
"default".into(),
ApprovalMode::Supervised,
false,
Some(expected.into()),
);
mapper.start_turn();
let events = mapper.on_message(json!({
"type": "assistant",
"message": { "id": "msg-change", "model": served, "content": [] },
"parent_tool_use_id": null,
}));
let changes: Vec<_> = events
.iter()
.filter(|event| matches!(event, AgentEvent::ModelFallbackDetected { .. }))
.collect();
assert_eq!(
served_model_is_fallback(expected, served),
is_fallback,
"expected={expected}, served={served}"
changes.len(),
usize::from(changed),
"{expected} -> {served}"
);
if changed {
assert!(matches!(changes[0], AgentEvent::ModelFallbackDetected {
expected: requested, actual, category: None,
checkpoint_id: None, parent_tool_use_id: None,
} if requested == expected && actual == served));
}
}

let expected = "claude-opus-5[1m]";
let normalized_expected = expected.split('[').next().unwrap_or(expected);
assert!(served_model_is_fallback(
normalized_expected,
"claude-opus-4-8"
));
}

#[test]
fn assistant_model_mismatch_emits_one_fallback_per_turn() {
fn model_changes_are_detected_at_stream_start_once_per_turn() {
let mut mapper = Mapper::new_configured(
false,
InteractionMode::Build,
"default",
"default".into(),
ApprovalMode::Supervised,
false,
Some("claude-fable-5".into()),
);
mapper.start_turn();

let first = feed(
&mut mapper,
r#"{"type":"assistant","message":{"id":"msg-fallback-1","model":"claude-opus-4-8","content":[]},"parent_tool_use_id":null}"#,
);
assert_eq!(
first
.iter()
.filter(|event| matches!(event, AgentEvent::ModelFallbackDetected { .. }))
.count(),
1
);
assert!(first.iter().any(|event| matches!(
event,
AgentEvent::ModelFallbackDetected {
expected,
actual,
category: None,
checkpoint_id: None,
parent_tool_use_id: None,
} if expected == "claude-fable-5"
&& actual == "claude-opus-4-8"
)));
Some("claude-fable-5-1".into()),
);
for served in ["claude-opus-5", "claude-opus-4-8", "claude-fable-5"] {
let stream = json!({
"type": "stream_event",
"event": { "type": "message_start", "message": {
"id": "msg-change", "model": served,
} },
"parent_tool_use_id": null,
});
for _ in 0..2 {
mapper.start_turn();
// A child using another model must not consume the parent's guard.
let mut child = stream.clone();
child["parent_tool_use_id"] = json!("child-tool");
let child_events = mapper.on_message(child);
assert!(
!child_events
.iter()
.any(|event| matches!(event, AgentEvent::ModelFallbackDetected { .. }))
);
let first = mapper.on_message(stream.clone());
assert_eq!(
first
.iter()
.filter(|event| matches!(
event, AgentEvent::ModelFallbackDetected { expected, actual, .. }
if expected == "claude-fable-5-1" && actual == served
))
.count(),
1
);
let repeated = mapper.on_message(stream.clone());
let completed = mapper.on_message(json!({
"type": "assistant", "message": {
"id": "msg-change", "model": served, "content": [],
}, "parent_tool_use_id": null,
}));
assert!(
!repeated
.iter()
.chain(&completed)
.any(|event| matches!(event, AgentEvent::ModelFallbackDetected { .. }))
);
}
}
}

let second = feed(
&mut mapper,
r#"{"type":"assistant","message":{"id":"msg-fallback-2","model":"claude-opus-4-8","content":[]},"parent_tool_use_id":null}"#,
);
assert!(
!second
.iter()
.any(|event| matches!(event, AgentEvent::ModelFallbackDetected { .. }))
);
#[test]
fn explicit_model_changes_ignore_only_context_suffix_differences() {
for (actual, changed) in [("claude-opus-5", false), ("claude-opus-4-8", true)] {
let mut mapper = Mapper::new();
let events = mapper.on_message(json!({
"type": "system", "subtype": "model_refusal_fallback",
"original_model": "claude-opus-5[1m]", "fallback_model": actual,
}));
assert_eq!(
events
.iter()
.filter(|event| matches!(event, AgentEvent::ModelFallbackDetected { .. }))
.count(),
usize::from(changed)
);
}
}

#[test]
Expand Down
28 changes: 23 additions & 5 deletions crates/runtime/src/app/events.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -364,18 +364,35 @@ impl AppState {
..
} => {
if self.settings.abort_on_model_fallback {
let is_active = self
let stopped_turn = self
.residents
.live
.get_mut(session_id)
.filter(|active| active.meta.id == session_id)
.is_some_and(|active| {
.map(|active| {
let turn_id = active
.timeline
.turns
.last()
.and_then(|turn| turn.provider_turn_id.clone())
.unwrap_or_default();
active.queue.clear();
active.timeline.mark_idle();
active.shutdown_to_idle();
true
turn_id
});
if is_active {
if let Some(turn_id) = stopped_turn {
// Shutdown drops the provider pump, so its completion cannot
// close the persisted turn or the clients' running indicators.
self.record_event(session_id, &event, cx);
self.on_event(
session_id,
AgentEvent::TurnCompleted {
turn_id,
status: TurnStatus::Interrupted,
usage: None,
},
cx,
);
self.emit_domain(
Topic::SessionStatus {
session_id: session_id.to_owned(),
Expand All @@ -389,6 +406,7 @@ impl AppState {
},
cx,
);
return;
}
}
}
Expand Down
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