diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 2c29f86dc..a82ad9f7b 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -265,6 +265,16 @@ jobs:
       - name: cargo test --workspace -- --skip dst_
         run: cargo test --workspace -- --skip dst_
 
+      # spec_validate_endpoint declares required-features = ["observe"]. The
+      # workspace run above usually still covers it via feature unification
+      # (temper-cli/temper-mcp enable temper-server's observe feature), but
+      # that coverage is incidental — it evaporates if those edges change.
+      # Run the observe-gated tests explicitly so coverage is guaranteed.
+      - name: cargo test observe-gated tests
+        run: |
+          cargo test -p temper-server --features observe --test spec_validate_endpoint
+          cargo test -p temper-server --features observe --lib observe::
+
   # ─────────────────────────────────────────────────────
   # Gate 3b: DST/platform coverage (matrixed)
   # ─────────────────────────────────────────────────────
diff --git a/crates/temper-server/Cargo.toml b/crates/temper-server/Cargo.toml
index 6ce2378df..0ed9c51e5 100644
--- a/crates/temper-server/Cargo.toml
+++ b/crates/temper-server/Cargo.toml
@@ -6,6 +6,10 @@ license.workspace = true
 rust-version.workspace = true
 description = "HTTP server assembly for Temper entity services"
 
+[[test]]
+name = "spec_validate_endpoint"
+required-features = ["observe"]
+
 [features]
 default = []
 observe = ["temper-verify"]
diff --git a/crates/temper-server/src/observe/mod.rs b/crates/temper-server/src/observe/mod.rs
index fbd3e3cfd..8a0c58f78 100644
--- a/crates/temper-server/src/observe/mod.rs
+++ b/crates/temper-server/src/observe/mod.rs
@@ -74,6 +74,25 @@ pub struct ActionDetail {
     pub guards: Vec<String>,
     /// Effects (Debug representation).
     pub effects: Vec<String>,
+    /// Parameters this action accepts, in spec order.
+    #[serde(default)]
+    pub params: Vec<ActionParamDetail>,
+    /// Agent-facing hint from the spec (empty when the spec has none).
+    #[serde(default)]
+    pub hint: String,
+}
+
+/// A single action parameter: name plus its declared type ("string" default).
+#[derive(Serialize, Deserialize)]
+pub struct ActionParamDetail {
+    /// Parameter name exactly as declared in the spec's `params` list.
+    pub name: String,
+    /// Declared parameter type, serialized under the JSON key `"type"`.
+    /// Bare-named params carry `"string"`; typed params carry the spec's
+    /// type name (e.g. `"uint64"`). This is an OPEN set — generated clients
+    /// must not assume a closed enum.
+    #[serde(rename = "type")]
+    pub param_type: String,
 }
 
 /// Detail of a single invariant.
diff --git a/crates/temper-server/src/observe/mod_test.rs b/crates/temper-server/src/observe/mod_test.rs
index b5bf6abd0..9c7a44460 100644
--- a/crates/temper-server/src/observe/mod_test.rs
+++ b/crates/temper-server/src/observe/mod_test.rs
@@ -874,6 +874,66 @@ async fn test_get_spec_detail_found() {
     assert_eq!(detail.entity_type, "Order");
     assert!(!detail.states.is_empty());
     assert!(!detail.actions.is_empty());
+
+    // The params/hint contract (consumed by generated typed clients):
+    // AddItem declares two bare-named params (default "string" type, spec
+    // order preserved) and a hint; RemoveItem declares no hint (empty, not
+    // null).
+    let add_item = detail
+        .actions
+        .iter()
+        .find(|a| a.name == "AddItem")
+        .expect("Order fixture declares AddItem");
+    let param_pairs: Vec<(&str, &str)> = add_item
+        .params
+        .iter()
+        .map(|p| (p.name.as_str(), p.param_type.as_str()))
+        .collect();
+    assert_eq!(
+        param_pairs,
+        vec![("ProductId", "string"), ("Quantity", "string")]
+    );
+    assert!(add_item.hint.starts_with("Add a product"));
+    let remove_item = detail
+        .actions
+        .iter()
+        .find(|a| a.name == "RemoveItem")
+        .expect("Order fixture declares RemoveItem");
+    assert_eq!(remove_item.params.len(), 1);
+    assert_eq!(remove_item.params[0].name, "ItemId");
+    assert_eq!(remove_item.hint, "");
+
+    // Wire-level contract: the type field serializes under the key "type",
+    // and params are objects, not bare strings.
+    let raw: serde_json::Value = serde_json::from_slice(&body).unwrap();
+    let raw_add_item = raw["actions"]
+        .as_array()
+        .unwrap()
+        .iter()
+        .find(|a| a["name"] == "AddItem")
+        .unwrap();
+    assert_eq!(raw_add_item["params"][0]["name"], "ProductId");
+    assert_eq!(raw_add_item["params"][0]["type"], "string");
+    assert_eq!(raw_add_item["hint"], add_item.hint);
+}
+
+#[test]
+fn action_param_detail_serializes_typed_params_under_type_key() {
+    // Typed params (e.g. `{ name = "sleep_seconds", type = "uint64" }` in a
+    // spec) reach ActionParamDetail through ActionParam::name()/param_type();
+    // this locks the wire shape those values serialize into.
+    let detail = ActionParamDetail {
+        name: "sleep_seconds".to_string(),
+        param_type: "uint64".to_string(),
+    };
+    let json = serde_json::to_value(&detail).unwrap();
+    assert_eq!(
+        json,
+        serde_json::json!({"name": "sleep_seconds", "type": "uint64"})
+    );
+    let back: ActionParamDetail = serde_json::from_value(json).unwrap();
+    assert_eq!(back.name, "sleep_seconds");
+    assert_eq!(back.param_type, "uint64");
 }
 
 #[tokio::test]
diff --git a/crates/temper-server/src/observe/specs.rs b/crates/temper-server/src/observe/specs.rs
index dab48e848..69905e8c4 100644
--- a/crates/temper-server/src/observe/specs.rs
+++ b/crates/temper-server/src/observe/specs.rs
@@ -8,7 +8,9 @@ use crate::authz::{observe_tenant_scope, require_observe_auth};
 use crate::registry::VerificationStatus;
 use crate::state::ServerState;
 
-use super::{ActionDetail, InvariantDetail, SpecDetail, SpecSummary, StateVarDetail};
+use super::{
+    ActionDetail, ActionParamDetail, InvariantDetail, SpecDetail, SpecSummary, StateVarDetail,
+};
 
 mod load_dir;
 mod load_inline;
@@ -115,6 +117,15 @@ pub(crate) async fn handle_get_spec_detail(
                         to: a.to.clone(),
                         guards: a.guard.iter().map(|g| format!("{g:?}")).collect(),
                         effects: a.effect.iter().map(|e| format!("{e:?}")).collect(),
+                        params: a
+                            .params
+                            .iter()
+                            .map(|p| ActionParamDetail {
+                                name: p.name().to_string(),
+                                param_type: p.param_type().to_string(),
+                            })
+                            .collect(),
+                        hint: a.hint.clone().unwrap_or_default(),
                     })
                     .collect(),
                 invariants: automaton
diff --git a/crates/temper-server/tests/wasm_dispatch.rs b/crates/temper-server/tests/wasm_dispatch.rs
index 50c4b29ff..2619d3b1b 100644
--- a/crates/temper-server/tests/wasm_dispatch.rs
+++ b/crates/temper-server/tests/wasm_dispatch.rs
@@ -354,7 +354,7 @@ async fn persisted_wasm_modules_are_lazy_compiled_on_first_invoke() {
         "EchoTest",
         "echo-lazy-1",
         &["Done", "Failed"],
-        Duration::from_secs(5),
+        Duration::from_secs(45),
     )
     .await;
     assert_eq!(final_status, "Done");
@@ -423,7 +423,7 @@ async fn persisted_wasm_modules_with_legacy_db_blob_fallback_execute_after_start
         "EchoTest",
         "echo-legacy-hash",
         &["Done", "Failed"],
-        Duration::from_secs(5),
+        Duration::from_secs(45),
     )
     .await;
     assert_eq!(final_status, "Done");