fix: pre-load skills for subagents and fix dev-mode spawning (#918)

Co-authored-by: Letta <noreply@letta.com>

src/agent/subagents/builtin/reflection.md

@@ -75,9 +75,9 @@ All subsequent file operations target the worktree:
 
 ### Phase 2: Review Recent Conversation History
 
-Use the `searching-messages` skill (pre-loaded in
-`<loaded_skills>`) to search via `letta messages search`
-and `letta messages list`.
+Use `letta messages search` and `letta messages list`
+(documented in `<loaded_skills>` below) to search the
+parent agent's conversation history.
 
 **Sliding window through recent history:**
 

src/agent/subagents/manager.ts

@@ -517,6 +517,11 @@ function buildSubagentArgs(
     args.push("--max-turns", String(maxTurns));
   }
 
+  // Pre-load skills specified in the subagent config
+  if (config.skills.length > 0) {
+    args.push("--pre-load-skills", config.skills.join(","));
+  }
+
   return args;
 }
 
@@ -552,7 +557,7 @@ async function executeSubagent(
   }
 
   try {
-    const cliArgs = buildSubagentArgs(
+    let cliArgs = buildSubagentArgs(
       type,
       config,
       model,
@@ -566,14 +571,19 @@ async function executeSubagent(
     // Use the same binary as the current process, with fallbacks:
     // 1. LETTA_CODE_BIN env var (explicit override)
     // 2. Current process argv[1] if it's a .js file (built letta.js)
-    // 3. ./letta.js if running from dev (src/index.ts)
+    // 3. Dev mode: use process.execPath (bun) with the .ts script as first arg
     // 4. "letta" (global install)
     const currentScript = process.argv[1] || "";
-    const lettaCmd =
+    let lettaCmd =
       process.env.LETTA_CODE_BIN ||
       (currentScript.endsWith(".js") ? currentScript : null) ||
-      (currentScript.includes("src/index.ts") ? "./letta.js" : null) ||
       "letta";
+    // In dev mode (running .ts file via bun), use the runtime binary directly
+    // and prepend the script path to the CLI args
+    if (currentScript.endsWith(".ts") && !process.env.LETTA_CODE_BIN) {
+      lettaCmd = process.execPath; // e.g., /path/to/bun
+      cliArgs = [currentScript, ...cliArgs];
+    }
     // Pass parent agent ID so subagents can access parent's context (e.g., search history)
     let parentAgentId: string | undefined;
     try {

src/headless.ts

@@ -118,6 +118,7 @@ export async function handleHeadlessCommand(
       "permission-mode": { type: "string" },
       yolo: { type: "boolean" },
       skills: { type: "string" },
+      "pre-load-skills": { type: "string" },
       sleeptime: { type: "boolean" },
       "init-blocks": { type: "string" },
       "base-tools": { type: "string" },
@@ -264,6 +265,7 @@ export async function handleHeadlessCommand(
   const memfsFlag = values.memfs as boolean | undefined;
   const noMemfsFlag = values["no-memfs"] as boolean | undefined;
   const fromAfFile = values["from-af"] as string | undefined;
+  const preLoadSkillsRaw = values["pre-load-skills"] as string | undefined;
   const maxTurnsRaw = values["max-turns"] as string | undefined;
 
   // Parse and validate max-turns if provided
@@ -1104,6 +1106,32 @@ ${SYSTEM_REMINDER_CLOSE}
       if (skillsReminder) {
         pushPart(skillsReminder);
       }
+
+      // Pre-load specific skills' full content (used by subagents with skills: field)
+      if (preLoadSkillsRaw) {
+        const { readFile: readFileAsync } = await import("node:fs/promises");
+        const skillIds = preLoadSkillsRaw
+          .split(",")
+          .map((s) => s.trim())
+          .filter(Boolean);
+        const loadedContents: string[] = [];
+        for (const skillId of skillIds) {
+          const skill = skills.find((s) => s.id === skillId);
+          if (skill?.path) {
+            try {
+              const content = await readFileAsync(skill.path, "utf-8");
+              loadedContents.push(`<${skillId}>\n${content}\n</${skillId}>`);
+            } catch {
+              // Skill file not readable, skip
+            }
+          }
+        }
+        if (loadedContents.length > 0) {
+          pushPart(
+            `<loaded_skills>\n${loadedContents.join("\n\n")}\n</loaded_skills>`,
+          );
+        }
+      }
     } catch {
       // Skills discovery failed, skip
     }

src/index.ts

@@ -437,6 +437,7 @@ async function main(): Promise<void> {
         "include-partial-messages": { type: "boolean" },
         "from-agent": { type: "string" },
         skills: { type: "string" },
+        "pre-load-skills": { type: "string" },
         sleeptime: { type: "boolean" },
         "from-af": { type: "string" },
         import: { type: "string" },