diff --git a/navi/core/agent.py b/navi/core/agent.py
index 7b6b716..79814dc 100644
--- a/navi/core/agent.py
+++ b/navi/core/agent.py
@@ -241,6 +241,7 @@
         profile_id: str,
         max_iterations: int = 20,
         exclude_tools: list[str] | None = None,
+        briefing: str | None = None,
         custom_system_prompt: str | None = None,
         context_transfer: str | None = None,
         timeout_seconds: float = 300.0,
@@ -256,10 +257,13 @@
         Tools listed in exclude_tools are stripped from the tool list
         (use this to prevent recursion: exclude 'spawn_agent').
 
-        custom_system_prompt: injected after the profile's system prompt (overrides
-            profile.subagent_system_prompt if provided).
-        context_transfer: text passed from the parent's scratchpad context_transfer
-            section, injected as a priming exchange before the task message.
+        System prompt structure (completely separate from the parent's system prompt):
+          1. profile.subagent_system_prompt  — focused executor persona
+          2. custom_system_prompt            — optional role specialisation for this task
+          3. briefing                        — task context (credentials, paths, instructions)
+
+        context_transfer: text from the parent's scratchpad context_transfer section,
+            injected as a priming exchange before the task message.
         timeout_seconds: wall-clock timeout for the entire sub-agent run.
         """
         import time as _time
@@ -281,13 +285,20 @@
 
         mem = await self._memory_msg()
 
-        # Build subagent system prompt: profile.system_prompt + subagent-specific prompt.
-        # No persona, no profiles block — subagents are focused executors.
-        effective_subagent_prompt = custom_system_prompt or profile.subagent_system_prompt
-        subagent_sys_content = profile.system_prompt
-        if effective_subagent_prompt:
-            subagent_sys_content = subagent_sys_content + "\n\n---\n\n" + effective_subagent_prompt
-        subagent_sys_msg = Message(role="system", content=subagent_sys_content)
+        # Build subagent system prompt — completely separate from the parent's system prompt.
+        # No persona, no orchestrator instructions, no profiles block.
+        # Structure: executor persona → role specialisation → task context (briefing)
+        sys_parts: list[str] = []
+        if profile.subagent_system_prompt:
+            sys_parts.append(profile.subagent_system_prompt)
+        if custom_system_prompt:
+            sys_parts.append(custom_system_prompt)
+        if briefing:
+            sys_parts.append(f"## Task context\n\n{briefing}")
+        if not sys_parts:
+            # Fallback if profile has no subagent_system_prompt defined
+            sys_parts.append(profile.system_prompt)
+        subagent_sys_msg = Message(role="system", content="\n\n---\n\n".join(sys_parts))
 
         # Build initial context.
         # If context_transfer is provided, inject it as a priming exchange so the
diff --git a/navi/tools/spawn_agent.py b/navi/tools/spawn_agent.py
index b58b94e..2e54083 100644
--- a/navi/tools/spawn_agent.py
+++ b/navi/tools/spawn_agent.py
@@ -41,9 +41,10 @@
             "briefing": {
                 "type": "string",
                 "description": (
-                    "All context the sub-agent needs — it has zero knowledge of your conversation. "
+                    "All context the sub-agent needs, injected as a system-level instruction. "
                     "Include: IPs, credentials, file paths, prior findings, constraints, "
-                    "step-by-step instructions if helpful."
+                    "step-by-step instructions. The sub-agent has zero knowledge of your "
+                    "conversation — include everything it needs to act autonomously."
                 ),
             },
             "profile_id": {
@@ -91,19 +92,13 @@
         from navi.tools.scratchpad import get_section
 
         task = params["task"].strip()
-        briefing = (params.get("briefing") or "").strip()
+        briefing = (params.get("briefing") or "").strip() or None
         custom_system_prompt = (params.get("system_prompt") or "").strip() or None
         max_iterations = int(params.get("max_iterations") or 20)
 
-        # Compose user message: briefing provides context, task states the goal.
-        if briefing:
-            user_message = (
-                f"## Context\n\n{briefing}\n\n"
-                f"---\n\n"
-                f"## Task\n\n{task}"
-            )
-        else:
-            user_message = task
+        # task → user message (what to do)
+        # briefing → system prompt (context, credentials, instructions)
+        user_message = task
 
         # Resolve profile: explicit override → parent session's profile → first available
         profile_id = params.get("profile_id", "").strip()
@@ -117,7 +112,7 @@
         log.info("spawn_agent.start", profile_id=profile_id, max_iterations=max_iterations,
                  task_preview=task[:80], has_briefing=bool(briefing),
                  has_context_transfer=bool(context_transfer),
-                 has_custom_prompt=bool(custom_system_prompt))
+                 has_system_prompt=bool(custom_system_prompt))
 
         agent = Agent(
             session_store=None,          # ephemeral — no DB access
@@ -134,6 +129,7 @@
                 profile_id=profile_id,
                 max_iterations=max_iterations,
                 exclude_tools=["spawn_agent"],  # prevent recursion
+                briefing=briefing,
                 custom_system_prompt=custom_system_prompt,
                 context_transfer=context_transfer or None,
                 timeout_seconds=300.0,