diff --git a/server/src/agents/pool/start/spawn.rs b/server/src/agents/pool/start/spawn.rs
index 4e4367aa..1dffc363 100644
--- a/server/src/agents/pool/start/spawn.rs
+++ b/server/src/agents/pool/start/spawn.rs
@@ -263,7 +263,18 @@ pub(super) async fn run_agent_spawn(
         Some(_) => {
             // Keep the full rendered prompt as fallback if resume fails.
             let fallback = prompt;
-            (resume_context_owned.unwrap_or_default(), Some(fallback))
+            // claude-code's --resume requires a non-empty -p prompt unless the
+            // resumed session has a deferred-tool marker. Watchdog-killed
+            // sessions don't have one, so an empty -p aborts the CLI with
+            // "No deferred tool marker found... Provide a prompt to continue
+            // the conversation." We default to a brief "continue from
+            // PLAN.md" message when no gate-failure context was provided.
+            let resume_msg = resume_context_owned.filter(|s| !s.is_empty()).unwrap_or_else(
+                || {
+                    "Continue from your prior session. Read PLAN.md for your current state and pick up where you left off.".to_string()
+                },
+            );
+            (resume_msg, Some(fallback))
         }
         None => {
             if let Some(ctx) = resume_context_owned {