diff --git a/Cargo.lock b/Cargo.lock
index fc80f4d81..781078207 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -5166,7 +5166,7 @@ checksum = "9b4f627cb1b25917193a259e49bdad08f671f8d9708acfd5fe0a8c1455d87220"
 [[package]]
 name = "petri-attractor-steps"
 version = "0.1.0"
-source = "git+https://github.com/lithoscomputer/petri.git?branch=main#2548c104e1b0b5ac710abc59b25724d6b2c4d66d"
+source = "git+https://github.com/lithoscomputer/petri.git?branch=main#e94a2fec1a4c88de43c46ac527968f67f1753b2b"
 dependencies = [
  "async-trait",
  "globset",
@@ -5197,7 +5197,7 @@ dependencies = [
 [[package]]
 name = "petri-driver"
 version = "0.1.0"
-source = "git+https://github.com/lithoscomputer/petri.git?branch=main#2548c104e1b0b5ac710abc59b25724d6b2c4d66d"
+source = "git+https://github.com/lithoscomputer/petri.git?branch=main#e94a2fec1a4c88de43c46ac527968f67f1753b2b"
 dependencies = [
  "async-trait",
  "getrandom 0.3.4",
@@ -5217,7 +5217,7 @@ dependencies = [
 [[package]]
 name = "petri-engine"
 version = "0.1.0"
-source = "git+https://github.com/lithoscomputer/petri.git?branch=main#2548c104e1b0b5ac710abc59b25724d6b2c4d66d"
+source = "git+https://github.com/lithoscomputer/petri.git?branch=main#e94a2fec1a4c88de43c46ac527968f67f1753b2b"
 dependencies = [
  "petri-ir",
  "serde",
@@ -5229,7 +5229,7 @@ dependencies = [
 [[package]]
 name = "petri-execution"
 version = "0.1.0"
-source = "git+https://github.com/lithoscomputer/petri.git?branch=main#2548c104e1b0b5ac710abc59b25724d6b2c4d66d"
+source = "git+https://github.com/lithoscomputer/petri.git?branch=main#e94a2fec1a4c88de43c46ac527968f67f1753b2b"
 dependencies = [
  "async-trait",
  "petri-driver",
@@ -5253,7 +5253,7 @@ dependencies = [
 [[package]]
 name = "petri-executor"
 version = "0.1.0"
-source = "git+https://github.com/lithoscomputer/petri.git?branch=main#2548c104e1b0b5ac710abc59b25724d6b2c4d66d"
+source = "git+https://github.com/lithoscomputer/petri.git?branch=main#e94a2fec1a4c88de43c46ac527968f67f1753b2b"
 dependencies = [
  "async-trait",
  "libc",
@@ -5268,7 +5268,7 @@ dependencies = [
 [[package]]
 name = "petri-executor-sandbox"
 version = "0.1.0"
-source = "git+https://github.com/lithoscomputer/petri.git?branch=main#2548c104e1b0b5ac710abc59b25724d6b2c4d66d"
+source = "git+https://github.com/lithoscomputer/petri.git?branch=main#e94a2fec1a4c88de43c46ac527968f67f1753b2b"
 dependencies = [
  "async-trait",
  "petri-executor",
@@ -5290,7 +5290,7 @@ dependencies = [
 [[package]]
 name = "petri-frontend"
 version = "0.1.0"
-source = "git+https://github.com/lithoscomputer/petri.git?branch=main#2548c104e1b0b5ac710abc59b25724d6b2c4d66d"
+source = "git+https://github.com/lithoscomputer/petri.git?branch=main#e94a2fec1a4c88de43c46ac527968f67f1753b2b"
 dependencies = [
  "marked-yaml",
  "petri-ir",
@@ -5304,7 +5304,7 @@ dependencies = [
 [[package]]
 name = "petri-frontend-attractor"
 version = "0.1.0"
-source = "git+https://github.com/lithoscomputer/petri.git?branch=main#2548c104e1b0b5ac710abc59b25724d6b2c4d66d"
+source = "git+https://github.com/lithoscomputer/petri.git?branch=main#e94a2fec1a4c88de43c46ac527968f67f1753b2b"
 dependencies = [
  "minijinja",
  "petri-frontend",
@@ -5321,7 +5321,7 @@ dependencies = [
 [[package]]
 name = "petri-frontend-fabro"
 version = "0.1.0"
-source = "git+https://github.com/lithoscomputer/petri.git?branch=main#2548c104e1b0b5ac710abc59b25724d6b2c4d66d"
+source = "git+https://github.com/lithoscomputer/petri.git?branch=main#e94a2fec1a4c88de43c46ac527968f67f1753b2b"
 dependencies = [
  "petri-frontend",
  "petri-frontend-attractor",
@@ -5337,7 +5337,7 @@ dependencies = [
 [[package]]
 name = "petri-frontend-native"
 version = "0.1.0"
-source = "git+https://github.com/lithoscomputer/petri.git?branch=main#2548c104e1b0b5ac710abc59b25724d6b2c4d66d"
+source = "git+https://github.com/lithoscomputer/petri.git?branch=main#e94a2fec1a4c88de43c46ac527968f67f1753b2b"
 dependencies = [
  "petri-frontend",
  "petri-ir",
@@ -5348,7 +5348,7 @@ dependencies = [
 [[package]]
 name = "petri-ir"
 version = "0.1.0"
-source = "git+https://github.com/lithoscomputer/petri.git?branch=main#2548c104e1b0b5ac710abc59b25724d6b2c4d66d"
+source = "git+https://github.com/lithoscomputer/petri.git?branch=main#e94a2fec1a4c88de43c46ac527968f67f1753b2b"
 dependencies = [
  "regex",
  "serde",
@@ -5361,7 +5361,7 @@ dependencies = [
 [[package]]
 name = "petri-runtime"
 version = "0.1.0"
-source = "git+https://github.com/lithoscomputer/petri.git?branch=main#2548c104e1b0b5ac710abc59b25724d6b2c4d66d"
+source = "git+https://github.com/lithoscomputer/petri.git?branch=main#e94a2fec1a4c88de43c46ac527968f67f1753b2b"
 dependencies = [
  "async-trait",
  "petri-driver",
@@ -5382,7 +5382,7 @@ dependencies = [
 [[package]]
 name = "petri-steps"
 version = "0.1.0"
-source = "git+https://github.com/lithoscomputer/petri.git?branch=main#2548c104e1b0b5ac710abc59b25724d6b2c4d66d"
+source = "git+https://github.com/lithoscomputer/petri.git?branch=main#e94a2fec1a4c88de43c46ac527968f67f1753b2b"
 dependencies = [
  "async-trait",
  "petri-executor",
@@ -5398,7 +5398,7 @@ dependencies = [
 [[package]]
 name = "petri-store"
 version = "0.1.0"
-source = "git+https://github.com/lithoscomputer/petri.git?branch=main#2548c104e1b0b5ac710abc59b25724d6b2c4d66d"
+source = "git+https://github.com/lithoscomputer/petri.git?branch=main#e94a2fec1a4c88de43c46ac527968f67f1753b2b"
 dependencies = [
  "async-trait",
  "getrandom 0.3.4",
@@ -5413,7 +5413,7 @@ dependencies = [
 [[package]]
 name = "petri-testkit"
 version = "0.1.0"
-source = "git+https://github.com/lithoscomputer/petri.git?branch=main#2548c104e1b0b5ac710abc59b25724d6b2c4d66d"
+source = "git+https://github.com/lithoscomputer/petri.git?branch=main#e94a2fec1a4c88de43c46ac527968f67f1753b2b"
 dependencies = [
  "async-trait",
  "petri-driver",
diff --git a/lib/components/fabro-petri/tests/agent_usage.rs b/lib/components/fabro-petri/tests/agent_usage.rs
new file mode 100644
index 000000000..038e032f4
--- /dev/null
+++ b/lib/components/fabro-petri/tests/agent_usage.rs
@@ -0,0 +1,218 @@
+//! An agent stage's usage, from Petri's real step metrics to the projected
+//! stage: one agent stage runs on the real step registry against a scripted
+//! model whose primary route answers once and then fails mid-prompt, so the
+//! prompt continues on the fallback route. The finished stage keeps the
+//! usage Petri reported and files each route's share under the model that
+//! spent it, as `pebble.usage_by_model` breaks it down.
+//!
+//! Built-in Host scopes run in process without a plugin executable.
+
+use std::collections::BTreeMap;
+use std::path::{Path, PathBuf};
+use std::sync::Arc;
+use std::time::Duration;
+
+use fabro_petri::projection::{Item, RunView};
+use fabro_petri::runtime::RuntimeSpec;
+use fabro_store::platform_records::{PlatformRecord, RunCreatedRecord, StoredPlatformRecord};
+use fabro_types::{ModelRef, RunId, StageId, test_support as types_support};
+use lithos_llm::catalog::{ModelId, ProviderId};
+use lithos_llm::types::{ErrorKind, Usage};
+use pebble_coding_agent::test_support::{
+    ScriptedCall, ScriptedFailure, scripted_client, text_response, tool_call_response,
+};
+use petri_execution::events::{RunEvent, replay_run};
+use petri_execution::host::{self, HostRun};
+use petri_runtime::engine::Event;
+use petri_runtime::executor::Retention;
+use petri_runtime::frontend::CompileInputs;
+use petri_runtime::ir::RunStatus;
+use petri_runtime::{RunOptions, Runtime};
+use petri_store::{Access, MemoryRunStore, RunKey, RunStore};
+use serde_json::{Value, json};
+use smol_str::SmolStr;
+use tokio::fs;
+
+/// One agent stage on the native backend, on the scripted catalog's
+/// `test/model`.
+const AGENT_WORKFLOW: &str = r#"digraph Agent {
+    graph [goal="Say hello", backend="api", default_max_retries=0]
+    start [shape=Mdiamond]
+    exit [shape=Msquare]
+    work [shape=box, prompt="Say hello", model="model", provider="test", max_retries=0]
+    start -> work -> exit
+}"#;
+
+/// The scripted catalog's `small` is the stage model's one fallback.
+const AGENT_SETTINGS: &str = "_version = 1\n\n[workflow]\ngraph = \"workflow.fabro\"\n\n\
+                              [run.model.fallbacks]\n\"model\" = [\"test:small\"]\n";
+
+/// Write the agent bundle into `<root>/.fabro/workflows/agent`; the
+/// workflow file.
+async fn install_bundle(root: &Path) -> PathBuf {
+    let bundle = root.join(".fabro").join("workflows").join("agent");
+    fs::create_dir_all(&bundle)
+        .await
+        .expect("the bundle directory is creatable");
+    fs::write(bundle.join("workflow.fabro"), AGENT_WORKFLOW)
+        .await
+        .expect("the workflow is writable");
+    fs::write(bundle.join("workflow.toml"), AGENT_SETTINGS)
+        .await
+        .expect("the settings are writable");
+    bundle.join("workflow.fabro")
+}
+
+fn runtime(
+    run_dir: &Path,
+    run_id: &str,
+    model_client: lithos_llm::Client,
+    store: &Arc<MemoryRunStore>,
+) -> Runtime {
+    let mut options = RunOptions::new(run_dir);
+    options.grace = Duration::from_secs(2);
+    options.retention = Retention::Never;
+    options.echo = false;
+    options.run_key = Some(RunKey::new(run_id));
+    RuntimeSpec {
+        model_client: Some(model_client),
+        ..RuntimeSpec::default()
+    }
+    .runtime(true)
+    .store(Arc::clone(store) as Arc<dyn RunStore>)
+    .options(options)
+}
+
+/// Lower the bundle and run it to its end.
+async fn run(rt: &Runtime, workflow: &Path) {
+    let lowered = rt
+        .check(workflow, None, None, &CompileInputs::new())
+        .expect("the workflow file loads");
+    let graph = lowered
+        .graph
+        .unwrap_or_else(|| panic!("the workflow lowers: {:?}", lowered.diagnostics));
+    let report = host::run_configured(rt, HostRun::new(graph), |_, _| {})
+        .await
+        .expect("the run completes");
+    assert_eq!(
+        report.status,
+        RunStatus::Success,
+        "errors: {:?}; history: {:#?}",
+        report.state.errors(),
+        report.state.history()
+    );
+}
+
+/// The agent's finished step metrics, as Petri recorded them.
+fn agent_metrics(events: &[RunEvent]) -> BTreeMap<SmolStr, Value> {
+    events
+        .iter()
+        .find_map(|event| match event.engine() {
+            Some(Event::StepFinished { outcome, .. })
+                if outcome.metrics.custom.contains_key("pebble.usage") =>
+            {
+                Some(outcome.metrics.custom.clone())
+            }
+            _ => None,
+        })
+        .expect("the agent's step finished with its usage")
+}
+
+fn usage(value: &Value) -> Usage {
+    serde_json::from_value(value.clone()).expect("a usage")
+}
+
+fn model(provider: &str, model: &str) -> ModelRef {
+    ModelRef::new(ProviderId::new(provider), ModelId::new(model))
+}
+
+#[tokio::test]
+async fn a_fallback_mid_prompt_keeps_each_routes_usage_under_its_model() {
+    let root = tempfile::tempdir().expect("a temp dir");
+    let workflow = install_bundle(root.path()).await;
+    let run_id = RunId::new();
+    let (client, provider) = scripted_client(vec![
+        ScriptedCall::response(tool_call_response(
+            "shell",
+            "work",
+            json!({"command": "true"}),
+        )),
+        ScriptedCall::Failure(ScriptedFailure::retryable(
+            ErrorKind::Server,
+            "primary down",
+        )),
+        ScriptedCall::response(text_response("Hello from small.")),
+    ]);
+    let store = Arc::new(MemoryRunStore::new());
+    let rt = runtime(
+        &root.path().join("run"),
+        &run_id.to_string(),
+        client,
+        &store,
+    );
+
+    run(&rt, &workflow).await;
+
+    let requested: Vec<String> = provider
+        .requests()
+        .iter()
+        .map(|request| request.model().to_owned())
+        .collect();
+    assert_eq!(requested, ["test/model", "test/model", "test/small"]);
+
+    // The run's events, folded as the projector folds them: the run's
+    // `run.created` record first, then Petri's events in record order.
+    let logs = store
+        .open(&RunKey::new(run_id.to_string()), Access::Read)
+        .await
+        .expect("the run opens");
+    let events = replay_run(&*logs).await.expect("the record replays");
+    let mut spec = types_support::test_run_spec();
+    spec.run_id = run_id;
+    let created = StoredPlatformRecord {
+        seq:         1,
+        recorded_at: 0,
+        record:      PlatformRecord::RunCreated(RunCreatedRecord {
+            spec,
+            title: Some("Say hello".to_string()),
+            parent_id: None,
+            retried_from: None,
+            web_url: None,
+        }),
+        position:    None,
+    };
+    let mut view = RunView::new();
+    view.fold(&Item::Platform(&created), 1);
+    for (index, event) in events.iter().enumerate() {
+        view.fold(&Item::Petri(event), index as u64 + 2);
+    }
+    let projection = view.projection().expect("the run has a projection");
+    let stage = projection
+        .stage(&StageId::new("work", 1))
+        .expect("the agent stage is projected");
+
+    // Petri's breakdown, one entry per route in first-use order.
+    let metrics = agent_metrics(&events);
+    let routes = metrics["pebble.usage_by_model"]
+        .as_array()
+        .expect("Petri breaks the root's usage down by route");
+    assert_eq!(routes.len(), 2, "{metrics:?}");
+    let primary = usage(&routes[0]["usage"]);
+    let fallback = usage(&routes[1]["usage"]);
+    assert!(primary.total_tokens() > 0, "{metrics:?}");
+    assert!(fallback.total_tokens() > 0, "{metrics:?}");
+
+    // The stage keeps every token Petri reported, and each route's share
+    // stays under the model that spent it.
+    assert_eq!(stage.usage, usage(&metrics["pebble.usage"]));
+    assert_eq!(stage.usage, primary.saturating_add(fallback));
+    let rows: Vec<(ModelRef, Usage)> = stage
+        .usage_by_model
+        .iter()
+        .map(|row| (row.model.clone(), row.usage))
+        .collect();
+    assert_eq!(rows, [
+        (model("test", "model"), primary),
+        (model("test", "small"), fallback),
+    ]);
+}