diff --git a/tests/test_agent_chat_router.py b/tests/test_agent_chat_router.py
index fe4e6492..928c3183 100644
--- a/tests/test_agent_chat_router.py
+++ b/tests/test_agent_chat_router.py
@@ -522,3 +522,93 @@ async def test_lead_who_is_author_does_not_receive_own_message():
 
     slugs = [c[0] for c in bridge.calls]
     assert "coord" not in slugs
+
+
+# ---------------------------------------------------------------------------
+# System context (agent_manual) injection
+# ---------------------------------------------------------------------------
+
+def _a2a_project_channel_with_leads(members, leads, mode="quiet"):
+    return {
+        "id": "c1",
+        "type": "group",
+        "project_id": "proj-1",
+        "members": members,
+        "settings": {
+            "kind": "a2a",
+            "response_mode": mode,
+            "leads": leads,
+            "max_hops": 3,
+            "cooldown_seconds": 5,
+            "rate_cap_per_minute": 20,
+            "muted": [],
+        },
+    }
+
+
+@pytest.mark.asyncio
+async def test_manual_injected_as_first_system_message():
+    """context[0] passed to the bridge must be a system-role manual message."""
+    bridge = _FakeBridge()
+    state = _state_for({"name": "coord", "status": "running"}, bridge=bridge)
+    state.config.agents = [{"name": "coord", "status": "running"}]
+    from tinyagentos.chat.group_policy import GroupPolicy
+    state.group_policy = GroupPolicy()
+    router = AgentChatRouter(state)
+
+    msg = {"id": "m1", "author_id": "user", "author_type": "user",
+           "content": "@coord go", "metadata": {"hops_since_user": 0}}
+    ch = _a2a_project_channel_with_leads(["user", "coord"], leads=["coord"])
+    await router._route(msg, ch)
+
+    assert len(bridge.calls) == 1
+    _, enqueued = bridge.calls[0]
+    ctx = enqueued["context"]
+    assert ctx, "context must not be empty"
+    first = ctx[0]
+    assert first["role"] == "system"
+    # Spot-check for known manual content.
+    assert "@-mention routing" in first["content"]
+    assert "kanban board" in first["content"]
+
+
+@pytest.mark.asyncio
+async def test_manual_lead_branch_correct_for_lead():
+    """When the recipient is a lead, the lead branch text appears."""
+    bridge = _FakeBridge()
+    state = _state_for({"name": "coord", "status": "running"}, bridge=bridge)
+    state.config.agents = [{"name": "coord", "status": "running"}]
+    from tinyagentos.chat.group_policy import GroupPolicy
+    state.group_policy = GroupPolicy()
+    router = AgentChatRouter(state)
+
+    msg = {"id": "m1", "author_id": "user", "author_type": "user",
+           "content": "@coord go", "metadata": {"hops_since_user": 0}}
+    ch = _a2a_project_channel_with_leads(["user", "coord"], leads=["coord"])
+    await router._route(msg, ch)
+
+    _, enqueued = bridge.calls[0]
+    manual = enqueued["context"][0]["content"]
+    assert "You ARE designated lead" in manual
+    assert "You are NOT a lead" not in manual
+
+
+@pytest.mark.asyncio
+async def test_manual_non_lead_branch_correct_for_worker():
+    """When the recipient is not a lead, the non-lead branch text appears."""
+    bridge = _FakeBridge()
+    state = _state_for({"name": "worker", "status": "running"}, bridge=bridge)
+    state.config.agents = [{"name": "worker", "status": "running"}]
+    from tinyagentos.chat.group_policy import GroupPolicy
+    state.group_policy = GroupPolicy()
+    router = AgentChatRouter(state)
+
+    msg = {"id": "m1", "author_id": "user", "author_type": "user",
+           "content": "@worker do it", "metadata": {"hops_since_user": 0}}
+    ch = _a2a_project_channel_with_leads(["user", "worker"], leads=["coord"])
+    await router._route(msg, ch)
+
+    _, enqueued = bridge.calls[0]
+    manual = enqueued["context"][0]["content"]
+    assert "You are NOT a lead" in manual
+    assert "You ARE designated lead" not in manual
diff --git a/tests/test_agent_manual.py b/tests/test_agent_manual.py
new file mode 100644
index 00000000..a746ee85
--- /dev/null
+++ b/tests/test_agent_manual.py
@@ -0,0 +1,173 @@
+"""Tests for tinyagentos.agent_manual.build_manual."""
+import pytest
+
+from tinyagentos.agent_manual import build_manual
+
+
+# ---------------------------------------------------------------------------
+# Helpers
+# ---------------------------------------------------------------------------
+
+def _dm_channel():
+    return {"id": "c1", "type": "dm", "settings": {}}
+
+
+def _group_channel():
+    return {"id": "c2", "type": "group", "settings": {"response_mode": "quiet"}}
+
+
+def _a2a_project_channel(leads=None):
+    return {
+        "id": "c3",
+        "type": "group",
+        "project_id": "proj-1",
+        "settings": {
+            "kind": "a2a",
+            "leads": leads or [],
+        },
+    }
+
+
+def _token_estimate(text: str) -> float:
+    """Simple heuristic: words * 1.3 (matches spec)."""
+    return len(text.split()) * 1.3
+
+
+# ---------------------------------------------------------------------------
+# DM channel
+# ---------------------------------------------------------------------------
+
+class TestDMChannel:
+    def test_dm_has_header(self):
+        text = build_manual(_dm_channel(), "alice", [])
+        assert "taOS" in text
+        assert "operating manual" in text
+
+    def test_dm_has_dm_stub(self):
+        text = build_manual(_dm_channel(), "alice", [])
+        assert "1-on-1" in text or "direct-message" in text
+
+    def test_dm_no_verbs_section(self):
+        # The verbs section header must not appear (stub may mention the word)
+        text = build_manual(_dm_channel(), "alice", [])
+        assert "## 2. Project task verbs" not in text
+        assert "/new" not in text
+
+    def test_dm_no_lead_section(self):
+        text = build_manual(_dm_channel(), "alice", [])
+        assert "Lead vs non-lead" not in text
+
+    def test_dm_no_mention_routing_section(self):
+        # The section header must not appear (stub mentions the term to say it doesn't apply)
+        text = build_manual(_dm_channel(), "alice", [])
+        assert "## 1. @-mentions are how messages route" not in text
+
+    def test_dm_token_budget(self):
+        text = build_manual(_dm_channel(), "alice", [])
+        assert _token_estimate(text) <= 200, (
+            f"DM manual exceeds 200-token budget: {_token_estimate(text):.0f} tokens"
+        )
+
+
+# ---------------------------------------------------------------------------
+# Group channel without project_id
+# ---------------------------------------------------------------------------
+
+class TestGroupChannelNoProject:
+    def test_has_mention_section(self):
+        text = build_manual(_group_channel(), "alice", [])
+        assert "@-mention routing" in text
+
+    def test_has_quick_ref_section(self):
+        text = build_manual(_group_channel(), "alice", [])
+        assert "Quick reference" in text
+
+    def test_no_task_verbs_section(self):
+        text = build_manual(_group_channel(), "alice", [])
+        assert "kanban board" not in text
+
+    def test_no_lead_section(self):
+        text = build_manual(_group_channel(), "alice", [])
+        assert "Lead vs non-lead" not in text
+
+
+# ---------------------------------------------------------------------------
+# Project a2a channel — lead agent
+# ---------------------------------------------------------------------------
+
+class TestProjectA2AChannelLead:
+    def setup_method(self):
+        self.channel = _a2a_project_channel(leads=["coord"])
+        self.text = build_manual(self.channel, "coord", ["coord"])
+
+    def test_has_mention_section(self):
+        assert "@-mention routing" in self.text
+
+    def test_has_task_verbs_section(self):
+        assert "kanban board" in self.text
+
+    def test_has_lead_section(self):
+        assert "Lead vs non-lead" in self.text
+
+    def test_lead_branch_text(self):
+        assert "You ARE designated lead" in self.text
+
+    def test_has_quick_ref_section(self):
+        assert "Quick reference" in self.text
+
+    def test_no_non_lead_text(self):
+        assert "You are NOT a lead" not in self.text
+
+
+# ---------------------------------------------------------------------------
+# Project a2a channel — non-lead agent
+# ---------------------------------------------------------------------------
+
+class TestProjectA2AChannelNonLead:
+    def setup_method(self):
+        self.channel = _a2a_project_channel(leads=["coord"])
+        self.text = build_manual(self.channel, "worker", ["coord"])
+
+    def test_has_mention_section(self):
+        assert "@-mention routing" in self.text
+
+    def test_has_task_verbs_section(self):
+        assert "kanban board" in self.text
+
+    def test_has_lead_section(self):
+        assert "Lead vs non-lead" in self.text
+
+    def test_non_lead_branch_text(self):
+        assert "You are NOT a lead" in self.text
+
+    def test_has_quick_ref_section(self):
+        assert "Quick reference" in self.text
+
+    def test_no_lead_text(self):
+        assert "You ARE designated lead" not in self.text
+
+
+# ---------------------------------------------------------------------------
+# Project a2a channel — empty leads list
+# ---------------------------------------------------------------------------
+
+class TestProjectA2AEmptyLeads:
+    def test_empty_leads_gives_non_lead_branch(self):
+        channel = _a2a_project_channel(leads=[])
+        text = build_manual(channel, "worker", [])
+        assert "You are NOT a lead" in text
+        assert "You ARE designated lead" not in text
+
+
+# ---------------------------------------------------------------------------
+# Token budget — longest branch (lead in project a2a)
+# ---------------------------------------------------------------------------
+
+class TestTokenBudget:
+    def test_longest_branch_under_500_tokens(self):
+        channel = _a2a_project_channel(leads=["coord"])
+        text = build_manual(channel, "coord", ["coord"])
+        estimate = _token_estimate(text)
+        assert estimate <= 500, (
+            f"Manual exceeds 500-token budget: {estimate:.0f} estimated tokens"
+        )
diff --git a/tinyagentos/agent_chat_router.py b/tinyagentos/agent_chat_router.py
index d340693d..2ec77db5 100644
--- a/tinyagentos/agent_chat_router.py
+++ b/tinyagentos/agent_chat_router.py
@@ -142,6 +142,9 @@ async def _route_inner(self, message: dict, channel: dict) -> None:
                 logger.warning("context fetch failed for channel %s", channel.get("id"), exc_info=True)
                 context = []
 
+        leads = list((settings.get("leads") or []))  # post-PR #291
+        from tinyagentos.agent_manual import build_manual
+
         for agent_name in recipients:
             forced = force_by_slug.get(agent_name, False)
             if not forced:
@@ -165,6 +168,8 @@ async def _route_inner(self, message: dict, channel: dict) -> None:
                 )
                 continue
 
+            manual_text = build_manual(channel, agent_name, leads)
+            agent_context = [{"role": "system", "content": manual_text}, *context]
             await bridge.enqueue_user_message(
                 agent_name,
                 {
@@ -176,7 +181,7 @@ async def _route_inner(self, message: dict, channel: dict) -> None:
                     "created_at": message.get("created_at"),
                     "hops_since_user": next_hops,
                     "force_respond": forced,
-                    "context": context,
+                    "context": agent_context,
                     "thread_id": thread_id,
                 },
             )
diff --git a/tinyagentos/agent_manual.py b/tinyagentos/agent_manual.py
new file mode 100644
index 00000000..05a6cf61
--- /dev/null
+++ b/tinyagentos/agent_manual.py
@@ -0,0 +1,124 @@
+"""Always-on system context injector.
+
+build_manual returns a markdown string that is prepended as a system-role
+message to every agent's context window at chat-dispatch time.  It is a
+pure function: no IO, no globals beyond the constant strings below.
+"""
+from __future__ import annotations
+
+_HEADER = """\
+# taOS — operating manual (always-on system context)
+
+You are running inside taOS. You communicate with humans and other agents
+via chat channels. Read these primitives carefully — getting them right
+is the difference between productive collaboration and silent dropouts.
+"""
+
+_SECTION_MENTIONS = """\
+## 1. @-mentions are how messages route
+
+This channel uses @-mention routing. A reply with no @-tag reaches NO ONE.
+
+- `@<name>` — addresses one agent by name
+- `@all` — addresses every agent in the channel
+- `@humans` — pings the human(s); no agent reply
+
+When handing off work, ALWAYS @-tag the next agent in your reply.
+Without an @-tag the channel does not route and the conversation stalls.
+
+If you @-tag a teammate and they go silent for two turns, tag them again
+with a polite nudge.
+"""
+
+_SECTION_TASK_VERBS = """\
+## 2. Project task verbs (kanban board)
+
+In a project chat channel, drive the kanban board with these single-line
+verbs anywhere in your message:
+
+- `/new "<title>" [@<assignee>]` — create a new task; optional assignee
+- `/claim <tsk-id>` — claim a ready task as your own
+- `/release <tsk-id>` — release a claimed task back to ready
+- `/close <tsk-id> [<note>]` — close a task with optional outcome note
+
+The kanban board updates live. Task ids look like `tsk-abc123` and the
+system announces them when created.
+"""
+
+_SECTION_LEAD_IS = """\
+## 3. Lead vs non-lead
+
+You ARE designated lead on this project. You receive every message in
+this channel regardless of @-mentions. Drive task allocation; chase
+silent teammates with @-mentions; see the project through to delivery.
+"""
+
+_SECTION_NON_LEAD = """\
+## 3. Lead vs non-lead
+
+You are NOT a lead on this project. You only see messages where you're
+explicitly @-tagged. Always @-tag the next agent or the lead when you
+hand off your work.
+"""
+
+_SECTION_QUICK_REF = """\
+## 4. Quick reference
+
+| You want to… | Do this |
+|---|---|
+| Address one agent | `@<name>` |
+| Address everyone | `@all` |
+| Create a task | `/new "<title>" @<name>` |
+| Claim a task | `/claim tsk-XXX` |
+| Close a task | `/close tsk-XXX <note>` |
+| Hand off work | Reply with `@<next-agent>` + deliverable / task id |
+
+Full chat guide: `/docs/chat-guide`.
+"""
+
+_DM_STUB = """\
+This is a 1-on-1 direct-message channel. Both you and the human always
+see every message here. No @-mention routing or kanban verbs apply.
+"""
+
+
+def build_manual(channel: dict, agent_name: str, leads: list[str]) -> str:
+    """Return the operating manual for *agent_name* in *channel*.
+
+    Args:
+        channel:    The channel dict (needs ``type``, ``settings``,
+                    ``project_id`` keys — missing keys are handled safely).
+        agent_name: Recipient agent's slug/name.
+        leads:      List of lead agent names from ``channel.settings.leads``.
+
+    Returns:
+        A markdown string suitable for a ``role: "system"`` message.
+    """
+    channel_type = channel.get("type") or ""
+    project_id = channel.get("project_id")
+    settings = channel.get("settings") or {}
+    is_a2a = settings.get("kind") == "a2a"
+
+    # DM: header + stub only.
+    if channel_type == "dm":
+        return _HEADER + _DM_STUB
+
+    # Group / topic channels.
+    parts = [_HEADER]
+
+    # Section 1: @-mention routing (group and topic channels).
+    if channel_type in ("group", "topic"):
+        parts.append(_SECTION_MENTIONS)
+
+    # Sections 2 + 3: project a2a only.
+    if project_id and is_a2a:
+        parts.append(_SECTION_TASK_VERBS)
+        if agent_name in leads:
+            parts.append(_SECTION_LEAD_IS)
+        else:
+            parts.append(_SECTION_NON_LEAD)
+
+    # Section 4: always for non-DM.
+    parts.append(_SECTION_QUICK_REF)
+
+    return "\n".join(parts)
diff --git a/tinyagentos/routes/cluster.py b/tinyagentos/routes/cluster.py
index 04c404f5..fb549738 100644
--- a/tinyagentos/routes/cluster.py
+++ b/tinyagentos/routes/cluster.py
@@ -71,6 +71,13 @@ async def list_workers(request: Request):
     result = []
     for w in workers:
         d = asdict(w)
+        # signing_key is the worker's raw HMAC secret (bytes). Two reasons
+        # to strip it from API responses: (1) FastAPI's default encoder
+        # tries to utf-8 decode bytes fields, which crashes on random key
+        # material — the entire workers list 500s when any worker has a
+        # non-utf8 signing key, and (2) even when serialization didn't
+        # crash, the secret has no business being on the wire.
+        d.pop("signing_key", None)
         if registry is not None:
             tier_id, pot_caps = _potential_capabilities(w.hardware, registry)
             d["tier_id"] = tier_id