diff --git a/backend/apps/agents/manager/prompt/prompt_context.py b/backend/apps/agents/manager/prompt/prompt_context.py
index c92c3a44..73a0868d 100644
--- a/backend/apps/agents/manager/prompt/prompt_context.py
+++ b/backend/apps/agents/manager/prompt/prompt_context.py
@@ -442,7 +442,13 @@ AGENT_IDENTITY = (
 @typechecked
 def compose_system_prompt(default_prompt: Optional[str], mode_prompt: Optional[str], session_prompt: Optional[str], browser_ctx: Optional[str] = None, mcp_registry_ctx: Optional[str] = None, skills_catalog_ctx: Optional[str] = None) -> Optional[str]:
     # Identity always leads so it overrides the preset's Claude Code persona, even when the user has no custom default/mode/session prompt of their own.
-    parts = [AGENT_IDENTITY] + [p for p in (default_prompt, mode_prompt, session_prompt, mcp_registry_ctx, skills_catalog_ctx, browser_ctx) if p]
+    # The session prompt goes LAST with explicit priority framing: buried mid-prompt it was delivered but ignored on turn one (Haik's hackathon blocker; live-proven with a marker token both ways).
+    framed_session = (
+        "## Instructions from your operator (highest priority)\n"
+        "The person who configured this agent wrote the following. Follow it over any earlier "
+        "guidance in this prompt, starting from your very first reply.\n\n" + session_prompt
+    ) if session_prompt else None
+    parts = [AGENT_IDENTITY] + [p for p in (default_prompt, mode_prompt, mcp_registry_ctx, skills_catalog_ctx, browser_ctx, framed_session) if p]
     return "\n\n".join(parts)
 
 
diff --git a/backend/tests/test_session_prompt_position.py b/backend/tests/test_session_prompt_position.py
new file mode 100644
index 00000000..a4e18d06
--- /dev/null
+++ b/backend/tests/test_session_prompt_position.py
@@ -0,0 +1,39 @@
+"""A custom system prompt must actually bite on the FIRST message (Haik's hackathon blocker).
+
+The prompt was always DELIVERED (verified in the live CLI argv, and the model could quote it when
+asked), but it sat mid-prompt between the identity block and the MCP registry, after the whole
+default prompt, and the model ignored it: a marker-token drill on the packaged build showed 0/3
+arms applying it. Moving it last with explicit operator framing flipped all arms to applied.
+
+These pin the structural half of that fix, the part a unit test can hold: position and framing.
+The behavioural half lives in the live drill (scratchpad/sysprompt_test.sh pattern).
+"""
+from backend.apps.agents.manager.prompt.prompt_context import compose_system_prompt
+
+SESSION = "Always answer in pirate speak."
+DEFAULT = "Be helpful and concise."
+MODE = "You are in coding mode."
+
+
+def test_session_prompt_is_the_last_content_in_the_composed_prompt():
+    out = compose_system_prompt(DEFAULT, MODE, SESSION, "browser ctx", "mcp ctx", "skills ctx")
+    assert out is not None
+    assert out.rstrip().endswith(SESSION), "anything after the operator's words dilutes them again"
+
+
+def test_session_prompt_carries_priority_framing():
+    out = compose_system_prompt(DEFAULT, MODE, SESSION)
+    assert "highest priority" in out
+    assert "your very first reply" in out, "turn one is the reported failure; the framing must name it"
+    assert out.index("highest priority") < out.index(SESSION), "the framing introduces the prompt, not trails it"
+
+
+def test_no_session_prompt_means_no_framing_block():
+    out = compose_system_prompt(DEFAULT, MODE, None, "browser ctx")
+    assert "highest priority" not in out, "an empty operator block would be framing around nothing"
+    assert DEFAULT in out and "browser ctx" in out
+
+
+def test_default_and_mode_prompts_still_precede_context_blocks():
+    out = compose_system_prompt(DEFAULT, MODE, SESSION, "browser ctx", "mcp ctx")
+    assert out.index(DEFAULT) < out.index(MODE) < out.index("mcp ctx") < out.index(SESSION)