feat: allow /eval agent to load external fixture files

Quickstart.md

@@ -283,6 +283,12 @@ resolved relative to that fixture file and may not escape that root:
 cargo run --release -- --eval ./evals/local/external-readme-check.json --json
 ```
 
+The interactive agent eval command accepts the same fixture path:
+
+```text
+/eval agent ./evals/local/external-readme-check.json
+```
+
 ## A Good First Session
 
 Here is a simple sequence that exercises the whole product:

README.md

@@ -836,10 +836,12 @@ runtime.
 - **One-shot mode** — `small-harness --print "summarize this repo"` or
   `printf '…\n' | small-harness` for scripts and CI. Approval-gated tools
   are denied by default; pass `--allow-tools` to allow them.
-- **Agent eval CLI** — `small-harness --eval fix-failing-test [--model M] [--json]`
+- **Agent eval** — `small-harness --eval fix-failing-test [--model M] [--json]`
   runs a bundled eval fixture and exits 0/1 (for CI scripts). `--eval` can
   also point at a data-only fixture JSON file; its workspace is resolved
-  relative to that file and rejected if it escapes the fixture root.
+  relative to that file and rejected if it escapes the fixture root. In the
+  interactive TUI, `/eval agent <fixture.json>` accepts the same external
+  fixture path.
 - **Warmup.** Small Harness sends a 1-token request with the full system
   prompt + tools at startup so llama.cpp-derived engines have a hot
   prompt-eval cache before your first prompt. Disable with `WARMUP=false`.

src/commands/workflow.rs

@@ -253,6 +253,7 @@ async fn cmd_eval_agent(parts: &[&str], state: &AppState) -> Result<()> {
         };
         (vec![fixture], models)
     };
+    let fixtures = resolve_eval_agent_fixtures(&fixture_ids)?;
 
     let eval_dir = Path::new(&state.session_dir).join("evals");
     fs::create_dir_all(&eval_dir)?;
@@ -262,16 +263,14 @@ async fn cmd_eval_agent(parts: &[&str], state: &AppState) -> Result<()> {
     for spec in model_specs {
         let (backend_desc, model) = parse_eval_model(&spec, state);
         validate(&backend_desc)?;
-        for fixture_id in &fixture_ids {
-            let fixture = crate::agent_eval::fixture_by_id(fixture_id)
-                .ok_or_else(|| anyhow!("unknown agent eval fixture: {fixture_id}"))?;
+        for fixture in &fixtures {
             println!(
                 "  {DIM}agent eval {} · {} · {}{RESET}",
-                fixture_id,
+                fixture.id,
                 backend_desc.name.as_str(),
                 model
             );
-            let result = run_agent_eval(&state.config, &backend_desc, &model, &fixture).await?;
+            let result = run_agent_eval(&state.config, &backend_desc, &model, fixture).await?;
             println!(
                 "  {} {}{RESET}",
                 if result.passed {
@@ -297,6 +296,15 @@ async fn cmd_eval_agent(parts: &[&str], state: &AppState) -> Result<()> {
     Ok(())
 }
 
+fn resolve_eval_agent_fixtures(
+    fixture_specs: &[String],
+) -> Result<Vec<crate::agent_eval::AgentEvalFixture>> {
+    fixture_specs
+        .iter()
+        .map(|spec| crate::agent_eval::fixture_by_spec(spec))
+        .collect()
+}
+
 pub(super) fn cmd_batch(args: &str, state: &AppState) -> Result<()> {
     let parts: Vec<&str> = args.split_whitespace().collect();
     if parts.is_empty() {
@@ -870,3 +878,44 @@ fn truncate_string(s: &str, max_len: usize) -> String {
         format!("{}...", &s[..max_len.saturating_sub(3)])
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn eval_agent_resolves_external_fixture_specs() {
+        let dir = tempfile::tempdir().unwrap();
+        fs::create_dir_all(dir.path().join("workspace/basic/src")).unwrap();
+        fs::write(
+            dir.path().join("workspace/basic/Cargo.toml"),
+            "[package]\nname=\"x\"\nversion=\"0.1.0\"\nedition=\"2021\"\n",
+        )
+        .unwrap();
+        fs::write(
+            dir.path().join("workspace/basic/src/lib.rs"),
+            "pub fn add() {}\n",
+        )
+        .unwrap();
+        let fixture_path = dir.path().join("external.json");
+        fs::write(
+            &fixture_path,
+            r#"{
+              "id": "external-basic",
+              "prompt": "Read the library.",
+              "workspace": "workspace/basic",
+              "checks": [
+                { "type": "fileContains", "path": "src/lib.rs", "needle": "add" }
+              ]
+            }"#,
+        )
+        .unwrap();
+        let spec = fixture_path.to_str().unwrap();
+
+        let fixtures = resolve_eval_agent_fixtures(&[spec.to_string()]).unwrap();
+
+        assert_eq!(fixtures.len(), 1);
+        assert_eq!(fixtures[0].id, "external-basic");
+        assert!(fixtures[0].fixture_root.is_some());
+    }
+}