diff --git a/crates/temper-server/src/state/dispatch/actions.rs b/crates/temper-server/src/state/dispatch/actions.rs
index 4b0952ce..3d99c319 100644
--- a/crates/temper-server/src/state/dispatch/actions.rs
+++ b/crates/temper-server/src/state/dispatch/actions.rs
@@ -672,6 +672,7 @@ impl crate::state::ServerState {
             entity_id,
             action,
             agent_ctx,
+            dispatch_idempotency_key: idempotency_key.as_deref(),
             action_params: &action_params,
             await_integration,
         };
diff --git a/crates/temper-server/src/state/dispatch/adapter.rs b/crates/temper-server/src/state/dispatch/adapter.rs
index 02df3d44..b8177b16 100644
--- a/crates/temper-server/src/state/dispatch/adapter.rs
+++ b/crates/temper-server/src/state/dispatch/adapter.rs
@@ -73,6 +73,7 @@ impl crate::state::ServerState {
                     custom_effects: &custom_effects,
                     entity_state: &entity_state,
                     agent_ctx: &agent_ctx,
+                    dispatch_idempotency_key: None,
                     action_params: &action_params,
                     mode: WasmDispatchMode::Background,
                 };
diff --git a/crates/temper-server/src/state/dispatch/effects.rs b/crates/temper-server/src/state/dispatch/effects.rs
index 2b1d4a74..f202ed4c 100644
--- a/crates/temper-server/src/state/dispatch/effects.rs
+++ b/crates/temper-server/src/state/dispatch/effects.rs
@@ -24,6 +24,7 @@ pub(crate) struct PostDispatchContext<'a> {
     pub entity_id: &'a str,
     pub action: &'a str,
     pub agent_ctx: &'a AgentContext,
+    pub dispatch_idempotency_key: Option<&'a str>,
     pub action_params: &'a serde_json::Value,
     pub await_integration: bool,
 }
@@ -500,6 +501,7 @@ impl crate::state::ServerState {
                     custom_effects: &response.custom_effects,
                     entity_state: &response.state,
                     agent_ctx: ctx.agent_ctx,
+                    dispatch_idempotency_key: ctx.dispatch_idempotency_key,
                     action_params: ctx.action_params,
                     mode: super::WasmDispatchMode::Inline,
                 };
@@ -557,6 +559,7 @@ impl crate::state::ServerState {
                     custom_effects: &response.custom_effects,
                     entity_state: adapter_state,
                     agent_ctx: ctx.agent_ctx,
+                    dispatch_idempotency_key: None,
                     action_params: ctx.action_params,
                     mode: super::WasmDispatchMode::Inline,
                 };
diff --git a/crates/temper-server/src/state/dispatch/mod.rs b/crates/temper-server/src/state/dispatch/mod.rs
index 4a498aee..6143210d 100644
--- a/crates/temper-server/src/state/dispatch/mod.rs
+++ b/crates/temper-server/src/state/dispatch/mod.rs
@@ -45,6 +45,7 @@ pub(crate) struct WasmDispatchRequest<'a> {
     pub custom_effects: &'a [String],
     pub entity_state: &'a EntityState,
     pub agent_ctx: &'a AgentContext,
+    pub dispatch_idempotency_key: Option<&'a str>,
     pub action_params: &'a serde_json::Value,
     pub mode: WasmDispatchMode,
 }
@@ -394,6 +395,7 @@ impl crate::state::ServerState {
                     custom_effects: &custom_effects,
                     entity_state: &entity_state,
                     agent_ctx: &agent_ctx,
+                    dispatch_idempotency_key: None,
                     action_params: &action_params,
                     mode: WasmDispatchMode::Background,
                 };
diff --git a/crates/temper-server/src/state/dispatch/state_timeouts.rs b/crates/temper-server/src/state/dispatch/state_timeouts.rs
index b79fc2a9..a6d77ef8 100644
--- a/crates/temper-server/src/state/dispatch/state_timeouts.rs
+++ b/crates/temper-server/src/state/dispatch/state_timeouts.rs
@@ -1157,6 +1157,7 @@ queue_timeout_seconds = 30
             entity_id: "t-1",
             action: "__Created",
             agent_ctx: &agent_ctx,
+            dispatch_idempotency_key: None,
             action_params: &serde_json::json!({}),
             await_integration: false,
         };
diff --git a/crates/temper-server/src/state/dispatch/wasm.rs b/crates/temper-server/src/state/dispatch/wasm.rs
index 53c70bf5..a47e6be2 100644
--- a/crates/temper-server/src/state/dispatch/wasm.rs
+++ b/crates/temper-server/src/state/dispatch/wasm.rs
@@ -38,9 +38,23 @@ struct WasmDispatchCtx<'a> {
     entity_ref: WasmEntityRef<'a>,
     action: &'a str,
     agent_ctx: &'a AgentContext,
+    dispatch_idempotency_key: Option<&'a str>,
     mode: WasmDispatchMode,
 }
 
+fn agent_ctx_for_composite_wasm_result(
+    agent_ctx: &AgentContext,
+    dispatch_idempotency_key: Option<&str>,
+) -> AgentContext {
+    let mut composite_agent_ctx = agent_ctx.clone();
+    if composite_agent_ctx.idempotency_key.is_none()
+        && let Some(idempotency_key) = dispatch_idempotency_key
+    {
+        composite_agent_ctx.idempotency_key = Some(idempotency_key.to_string());
+    }
+    composite_agent_ctx
+}
+
 const HTTP_CALL_AUTHZ_DENIED_PREFIX: &str = "authorization denied for http_call";
 const MONTY_REPL_MODULE: &str = "monty_repl";
 const WASM_DISPATCH_PHASE_MODULE_CACHE: &str = "dispatch.wasm.phase.module_cache";
@@ -355,6 +369,7 @@ impl crate::state::ServerState {
             },
             action: req.action,
             agent_ctx: req.agent_ctx,
+            dispatch_idempotency_key: req.dispatch_idempotency_key,
             mode: req.mode,
         };
         let mut last_response: Option<EntityResponse> = None;
@@ -1121,6 +1136,10 @@ impl crate::state::ServerState {
                 .await;
 
                 let callback_params = strip_private_observability_params(result.callback_params);
+                let composite_agent_ctx = agent_ctx_for_composite_wasm_result(
+                    ctx.agent_ctx,
+                    ctx.dispatch_idempotency_key,
+                );
                 let composite_result_consumed = self
                     .apply_composite_integration_result(
                         ctx.entity_ref.tenant,
@@ -1128,7 +1147,7 @@ impl crate::state::ServerState {
                         ctx.entity_ref.entity_id,
                         ctx.action,
                         &callback_params,
-                        ctx.agent_ctx,
+                        &composite_agent_ctx,
                     )
                     .await
                     .map_err(|e| e.to_string())?;
@@ -2008,6 +2027,36 @@ fn progress_emitter_fn(
 mod tests {
     use super::*;
 
+    #[test]
+    fn composite_wasm_result_inherits_generated_dispatch_idempotency() {
+        let agent = AgentContext::for_service("version-publisher");
+
+        let composite_agent = agent_ctx_for_composite_wasm_result(
+            &agent,
+            Some("dispatch:default:App:app:PublishNewVersion:one"),
+        );
+
+        assert_eq!(
+            composite_agent.idempotency_key.as_deref(),
+            Some("dispatch:default:App:app:PublishNewVersion:one"),
+            "composite sub-writes need the parent dispatch idempotency so repeated app version updates get distinct sub-write keys"
+        );
+    }
+
+    #[test]
+    fn composite_wasm_result_preserves_caller_supplied_idempotency() {
+        let mut agent = AgentContext::for_service("version-publisher");
+        agent.idempotency_key = Some("caller-key".to_string());
+
+        let composite_agent = agent_ctx_for_composite_wasm_result(&agent, Some("generated-key"));
+
+        assert_eq!(
+            composite_agent.idempotency_key.as_deref(),
+            Some("caller-key"),
+            "caller idempotency remains authoritative for retries"
+        );
+    }
+
     #[test]
     fn strips_private_llm_observability_params_before_callback_dispatch() {
         let params = json!({
@@ -2183,6 +2232,7 @@ mod tests {
                 },
                 action: "ContextReady",
                 agent_ctx: &agent_ctx,
+                dispatch_idempotency_key: None,
                 mode: WasmDispatchMode::Inline,
             };
             let span = build_llm_root_span(&ctx, &integration, &entity_state, "provider_caller");