fix(agent): raise combined system prompt cap to 1 MiB

crates/buzz-agent/src/config.rs

@@ -3,7 +3,10 @@ use std::time::Duration;
 pub const PROTOCOL_VERSION: u32 = 2;
 
 pub const MAX_PROMPT_BYTES: usize = 1024 * 1024;
-pub const MAX_SYSTEM_PROMPT_BYTES: usize = 512 * 1024;
+/// Ceiling on the combined system prompt (harness prompt + persona + hints).
+/// Raised from 512 KiB to 1 MiB to fit large discovered skill/AGENTS.md hint
+/// sections; matches `MAX_PROMPT_BYTES`.
+pub const MAX_SYSTEM_PROMPT_BYTES: usize = 1024 * 1024;
 /// Total per-result byte ceiling (text + images). Sized for image-bearing
 /// results — view_image can legitimately return multi-MiB base64 payloads.
 /// Text is governed by the much smaller `BUZZ_AGENT_MAX_TOOL_RESULT_TEXT_BYTES`.

crates/buzz-agent/src/lib.rs

@@ -285,7 +285,7 @@ async fn session_new(app: &Arc<App>, id: Value, params: Value, wire_tx: &WireSen
         } else {
             format!("{base}\n\n{hints}")
         };
-        // Reject combined prompts exceeding 512KB.
+        // Reject combined prompts exceeding MAX_SYSTEM_PROMPT_BYTES.
         if prompt.len() > MAX_SYSTEM_PROMPT_BYTES {
             return reject(
                 wire_tx,

crates/buzz-agent/tests/fake_llm.rs

@@ -423,7 +423,7 @@ async fn rejects_oversized_line() {
 
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
 async fn session_new_rejects_oversized_system_prompt() {
-    // A systemPrompt exceeding 512KB must produce a JSON-RPC error, not a panic.
+    // A systemPrompt exceeding 1 MiB must produce a JSON-RPC error, not a panic.
     let url = spawn_fake_llm(vec![]).await;
     let mut h = Harness::spawn(&url).await;
     h.send(
@@ -434,8 +434,8 @@ async fn session_new_rejects_oversized_system_prompt() {
     let r = h.recv().await;
     assert_eq!(r["result"]["protocolVersion"], 2);
 
-    // 600KB payload — exceeds the 512KB limit.
-    let big_prompt = "x".repeat(600 * 1024);
+    // 1100KB payload — exceeds the 1 MiB limit.
+    let big_prompt = "x".repeat(1100 * 1024);
     let id = h
         .send(
             "session/new",
@@ -449,8 +449,8 @@ async fn session_new_rejects_oversized_system_prompt() {
     );
     let err_msg = r["error"]["message"].as_str().unwrap_or("");
     assert!(
-        err_msg.contains("512KB limit"),
-        "error message should mention 512KB limit, got: {err_msg}"
+        err_msg.contains("1024KB limit"),
+        "error message should mention 1024KB limit, got: {err_msg}"
     );
     h.shutdown().await;
 }