feat(studio-cp,oab-mcp): K8sFleetBinding.expected_principal + k8s_fleet_config_write (studio#104)

crates/oab-mcp/src/lib.rs

@@ -245,6 +245,17 @@ pub fn tools() -> Vec<Tool> {
                 "required": ["namespace"]
             })),
         ),
+        Tool::new(
+            "k8s_fleet_config_write",
+            "Persist the whole k8s fleet-binding config (fleets-k8s.toml, separate from AWS's fleets.toml) from raw TOML `text`. Validates the text parses before writing — a bad edit never lands on disk — and the bytes are stored verbatim, so comments/layout are preserved. Returns the parsed fleets (name, context, namespace, members, expected_principal) plus the raw text. Write tool: overwrites the operator's fleets-k8s.toml.",
+            as_map(json!({
+                "type": "object",
+                "properties": {
+                    "text": { "type": "string", "description": "Full TOML document for fleets-k8s.toml (a list of [fleet.<name>] tables)." }
+                },
+                "required": ["text"]
+            })),
+        ),
     ]
 }
 
@@ -361,6 +372,7 @@ impl OabMcp {
             "list_k8s_contexts" => self.t_list_k8s_contexts(args),
             "list_namespaces" => self.t_list_namespaces(args).await,
             "list_service_accounts" => self.t_list_service_accounts(args).await,
+            "k8s_fleet_config_write" => self.t_k8s_fleet_write(args),
             other => anyhow::bail!("unknown tool {other:?}"),
         }
     }
@@ -794,6 +806,38 @@ impl OabMcp {
         Ok(json!({ "service_accounts": service_accounts }))
     }
 
+    /// Write tool: persist the whole `fleets-k8s.toml` from the editor's
+    /// `text` after validating it parses, mirroring `t_fleet_write`'s
+    /// AWS-side shape. Unlike AWS bindings, k8s bindings aren't cached
+    /// anywhere in `OabMcp` yet (nothing here dispatches provisioning to
+    /// `K8sDriver` yet either — that's a separate item), so this is a plain
+    /// validate-then-write with no in-memory state to invalidate.
+    fn t_k8s_fleet_write(&self, args: &Map<String, Value>) -> Result<Value> {
+        let text = args
+            .get("text")
+            .and_then(Value::as_str)
+            .ok_or_else(|| anyhow::anyhow!("missing required arg: text"))?;
+        let path = scp::default_k8s_bindings_path()
+            .ok_or_else(|| anyhow::anyhow!("no k8s fleet config path resolved; cannot write bindings"))?;
+        let bindings = scp::save_k8s_bindings_text(&path, text)?;
+        let fleets: Vec<Value> = bindings
+            .fleets
+            .iter()
+            .map(|b| json!({
+                "name": b.name,
+                "context": b.context,
+                "namespace": b.namespace,
+                "members": b.members,
+                "expected_principal": b.expected_principal,
+            }))
+            .collect();
+        Ok(json!({
+            "path": path.display().to_string(),
+            "fleets": fleets,
+            "text": text,
+        }))
+    }
+
     async fn t_delete(&self, args: &Map<String, Value>) -> Result<Value> {
         let t = self.target(args)?;
         let cluster = t.cluster.clone();
@@ -876,7 +920,7 @@ mod tests {
             .iter()
             .map(|t| t["name"].as_str().expect("tool has a name").to_string())
             .collect();
-        assert_eq!(names.len(), 15);
+        assert_eq!(names.len(), 16);
         for expected in [
             "deploy_list",
             "deploy_get",
@@ -893,6 +937,7 @@ mod tests {
             "list_k8s_contexts",
             "list_namespaces",
             "list_service_accounts",
+            "k8s_fleet_config_write",
         ] {
             assert!(names.contains(&expected.to_string()), "missing {expected}");
         }

crates/studio-cp/src/lib.rs

@@ -809,6 +809,15 @@ pub struct K8sFleetBinding {
     /// `FleetBinding`'s empty-members-means-everything convention).
     #[serde(default)]
     pub members: Vec<String>,
+    /// Expected principal to verify the resolved k8s identity against —
+    /// same name and verify semantics as `FleetBinding::expected_principal`
+    /// (`observe_identity`/`identity_matches` for AWS), just compared against
+    /// `observe_k8s_identity`'s `SelfSubjectReview`-derived principal instead
+    /// of an STS caller ARN. Typically `system:serviceaccount:<ns>:<name>`
+    /// for a service account, or a plain username. `None` = no identity
+    /// verification for this fleet (same "unset = don't check" contract).
+    #[serde(default)]
+    pub expected_principal: Option<String>,
 }
 
 impl K8sFleetBinding {
@@ -828,6 +837,8 @@ struct K8sFleetBody {
     namespace: String,
     #[serde(default)]
     members: Vec<String>,
+    #[serde(default)]
+    expected_principal: Option<String>,
 }
 
 #[derive(serde::Deserialize)]
@@ -847,6 +858,7 @@ impl From<K8sFleetsDoc> for K8sFleetBindings {
                     context: b.context,
                     namespace: b.namespace,
                     members: b.members,
+                    expected_principal: b.expected_principal,
                 })
                 .collect(),
         }
@@ -1389,13 +1401,32 @@ namespace = "prod"
         assert_eq!(prod.context, None);
     }
 
+    #[test]
+    fn k8s_fleet_expected_principal_parses_and_defaults_to_none() {
+        let doc = r#"
+[fleet.dev]
+namespace = "dev"
+expected_principal = "system:serviceaccount:dev:oab-agent"
+
+[fleet.unset]
+namespace = "prod"
+"#;
+        let b: K8sFleetBindings = toml::from_str(doc).expect("parse");
+        assert_eq!(
+            b.get("dev").expect("dev fleet").expected_principal.as_deref(),
+            Some("system:serviceaccount:dev:oab-agent")
+        );
+        assert_eq!(b.get("unset").expect("unset fleet").expected_principal, None);
+    }
+
     #[test]
     fn k8s_binding_includes_matches_by_name_or_whole_namespace() {
         let scoped = K8sFleetBinding {
             name: "dev".into(),
             context: Some("orbstack".into()),
             namespace: "dev".into(),
             members: vec!["scratch-agent".into()],
+            expected_principal: None,
         };
         assert!(scoped.includes("scratch-agent"));
         assert!(!scoped.includes("other-agent"));
@@ -1405,6 +1436,7 @@ namespace = "prod"
             context: None,
             namespace: "prod".into(),
             members: vec![],
+            expected_principal: None,
         };
         assert!(whole.includes("anything"));
     }