diff --git a/harbor/hooks.py b/harbor/hooks.py
index e2bccf3..ef6ad2f 100644
--- a/harbor/hooks.py
+++ b/harbor/hooks.py
@@ -63,7 +63,7 @@ ALLOWED_COMMANDS = {"brief", "inbox", "ack", "thread", "threads", "search", "tai
                     "tasks", "pins", "decisions", "handoffs", "handoff", "item", "pending-acks", "wait", "doing", "send",
                     "reply", "answer", "questions", "context", "notes", "note", "digest", "attention", "stop", "who",
                     "feed", "summarize", "git", "templates", "pulse", "metrics", "wins"}
-ALLOWED_TOOLS = {"brief", "inbox", "ack", "thread", "threads", "search", "status", "queue", "claims", "tasks", "handoff",
+ALLOWED_TOOLS = {"brief", "i_am", "mark_read", "inbox", "ack", "thread", "threads", "search", "status", "queue", "claims", "tasks", "handoff",
                  "send", "reply", "wait_for_messages", "doing", "questions", "answer", "context", "notes", "note",
                  "digest", "pin", "close_thread", "stop", "summarize", "who_knows", "git_status"}
 TOOL_NAME = re.compile(r"^(?:mcp__harbor__|harbor[_.])([a-z_]+)$")
@@ -276,6 +276,10 @@ def _run(event, harbor, agent, host, payload):
         try:                                                                # bookkeeping is best effort
             from .launch import describe_target
             tool_input = payload.get("tool_input") or payload.get("input") or {}
+            harbor_tool = _harbor_tool(str(tool))
+            if harbor_tool is not None:          # tell the app's shared Harbor server which session is calling
+                from . import sessions
+                sessions.leave(harbor, host, harbor_tool, tool_input if isinstance(tool_input, dict) else {}, agent)
             paths = harbor.edited_paths(tool, tool_input)
             harbor.activity(agent, tool, host, target=describe_target(tool, tool_input, paths))
             if not stops:
diff --git a/harbor/mcp_server.py b/harbor/mcp_server.py
index b75a59b..139af26 100644
--- a/harbor/mcp_server.py
+++ b/harbor/mcp_server.py
@@ -5,6 +5,7 @@ Run with the agent's identity fixed in its environment (it cannot be changed fro
 The project comes from $HARBOR_PROJECT or the .harbor.toml above the working directory. The human is refused.
 """
 import asyncio
+import contextvars
 import os
 import threading
 import time
@@ -14,8 +15,9 @@ os.environ.setdefault("FASTMCP_CHECK_FOR_UPDATES", "off")      # no network call
 os.environ.setdefault("FASTMCP_SHOW_SERVER_BANNER", "false")
 from fastmcp import FastMCP  # noqa: E402
 from fastmcp.exceptions import ToolError  # noqa: E402
+from fastmcp.server.middleware import Middleware  # noqa: E402
 
-from . import projects  # noqa: E402
+from . import projects, sessions  # noqa: E402
 from .core import OPEN_ITEM_STATES, Harbor, HarborError  # noqa: E402
 
 INSTRUCTIONS = """Harbor is the team's shared coordination store: messages in threads, acknowledgements, claims, a
@@ -55,6 +57,30 @@ ClaimKind = Literal["draft", "naming", "edit", "review", "band"]
 mcp = FastMCP("harbor", instructions=INSTRUCTIONS)
 _lock = threading.Lock()
 _state = {"seen": 0.0}
+_caller = contextvars.ContextVar("harbor_caller", default=None)    # the session behind the current tool call
+
+
+class SessionIdentity(Middleware):
+    """One app may share this server between several sessions (Codex and Codex2). The app's PreToolUse hook names
+    the calling session in a ticket; take it so this call runs as that agent (harbor.sessions)."""
+
+    async def on_call_tool(self, context, call_next):
+        agent = None
+        try:
+            message = context.message
+            with _lock:
+                agent = sessions.take(harbor(), os.environ.get("HARBOR_HOST", ""), message.name,
+                                      dict(message.arguments or {}))
+        except Exception:   # noqa: BLE001 - identity falls back to the server's own
+            agent = None
+        token = _caller.set(agent)
+        try:
+            return await call_next(context)
+        finally:
+            _caller.reset(token)
+
+
+mcp.add_middleware(SessionIdentity())
 
 
 def harbor():
@@ -67,9 +93,9 @@ def harbor():
 
 def me():
     h = harbor()
-    # a session bound with i_am, else the agent its working folder names (when it runs in the same app as the
-    # installed one: Codex and Codex2 share the Codex app), else the installed one
-    agent = _state.get("bound") or h.project.session_identity(os.environ.get("HARBOR_AGENT"), os.getcwd()) or ""
+    # the session its app's hook named for this call (several sessions can share this server), else the agent the
+    # server's working folder names when it runs in the same app as the installed one, else the installed one
+    agent = (_caller.get() or h.project.session_identity(os.environ.get("HARBOR_AGENT"), os.getcwd()) or "")
     if agent not in h.project.ai_names:
         raise HarborError(f"HARBOR_AGENT must be one of {', '.join(h.project.ai_names)} (set it in this server's MCP "
                           "config)")
@@ -125,22 +151,19 @@ def run(fn):
 
 @mcp.tool
 def i_am(agent: str) -> dict:
-    """Say which of the project's agents this session is, when one app runs several (Codex and Codex2). Call it once
-    at the start of the session if your instructions or your working folder name you; only an agent of the same
-    app is accepted, and a server already bound to another agent refuses."""
+    """Check which of the project's agents Harbor takes this session to be, when one app runs several (Codex and
+    Codex2). Call it at the start of the session with the name your instructions give you. Harbor knows the session
+    from its working folder (through the app's hooks); if the answer is not you, stop and tell the user."""
     def do(h):
-        pinned = os.environ.get("HARBOR_AGENT") or ""
         if agent not in h.project.ai_names:
             raise HarborError(f"{agent} is not one of {', '.join(h.project.ai_names)}")
-        if pinned and h.project.host_of(agent) != h.project.host_of(pinned):
-            raise HarborError(f"{agent} runs in another app ({h.project.host_of(agent) or 'unknown'}), not this one")
-        bound = _state.get("bound")
-        if bound and bound != agent:
-            raise HarborError(f"this Harbor server is already {bound}: the app shares one server between sessions, "
-                              "so give each session its own app profile instead")
-        _state["bound"] = agent
-        return {"you_are": agent, "working_folder": os.getcwd(),
-                "folder_says": h.project.identity_for(os.getcwd())}
+        seen = me()
+        out = {"you_are": seen, "matches": seen == agent}
+        if seen != agent:
+            out["fix"] = (f"Harbor sees this session as {seen}, not {agent}. Check that this session works in "
+                          f"{agent}'s own worktree and that the app's Harbor hooks are installed and trusted; do no "
+                          "work until it matches.")
+        return out
     return run(do)
 
 
diff --git a/harbor/sessions.py b/harbor/sessions.py
new file mode 100644
index 0000000..54a3e66
--- /dev/null
+++ b/harbor/sessions.py
@@ -0,0 +1,51 @@
+"""Which agent made this MCP call, when one app runs several sessions (Codex and Codex2) on one shared Harbor server.
+
+An app starts one Harbor MCP server and shares it between its sessions, so the server cannot tell them apart. The
+app's PreToolUse hook can: it runs before every tool call with the session's working folder. So the hook leaves a
+ticket (app, tool, arguments, agent) and the server takes the matching ticket when the call arrives - oldest first,
+within two minutes. Without a ticket (hooks not installed or not trusted) the server falls back to its own identity."""
+import json
+import time
+
+SCHEMA = """
+CREATE TABLE IF NOT EXISTS session_tickets(id INTEGER PRIMARY KEY, host TEXT NOT NULL, tool TEXT NOT NULL,
+    args TEXT NOT NULL, agent TEXT NOT NULL, at REAL NOT NULL, used INTEGER NOT NULL DEFAULT 0);
+CREATE INDEX IF NOT EXISTS session_tickets_open ON session_tickets(host, tool, used, at);
+"""
+MAX_AGE = 120.0
+
+
+def args_key(args):
+    return json.dumps(args or {}, sort_keys=True, separators=(",", ":"), default=str)
+
+
+def leave(harbor, host, tool, args, agent, now=None):
+    now = time.time() if now is None else now
+
+    def do(c):
+        c.execute("DELETE FROM session_tickets WHERE at < ?", (now - 10 * MAX_AGE,))
+        c.execute("INSERT INTO session_tickets(host, tool, args, agent, at) VALUES (?,?,?,?,?)",
+                  (host or "", tool, args_key(args), agent, now))
+    ensure(harbor)
+    harbor._write(do)
+
+
+def take(harbor, host, tool, args, now=None):
+    """The agent whose hook announced this exact call, or None."""
+    now = time.time() if now is None else now
+    ensure(harbor)
+
+    def do(c):
+        row = c.execute("SELECT id, agent FROM session_tickets WHERE host=? AND tool=? AND args=? AND used=0 AND at>=? "
+                        "ORDER BY at, id LIMIT 1", (host or "", tool, args_key(args), now - MAX_AGE)).fetchone()
+        if not row:
+            return None
+        c.execute("UPDATE session_tickets SET used=1 WHERE id=?", (row[0],))
+        return row[1]
+    return harbor._write(do)
+
+
+def ensure(harbor):
+    if not getattr(harbor, "_session_tickets_ready", False):
+        harbor.conn.executescript(SCHEMA)
+        harbor._session_tickets_ready = True
diff --git a/tests/test_interfaces.py b/tests/test_interfaces.py
index be49825..250cc30 100644
--- a/tests/test_interfaces.py
+++ b/tests/test_interfaces.py
@@ -288,6 +288,41 @@ class ServerWork(unittest.TestCase):
 
 
 class Mcp(unittest.TestCase):
+    def test_shared_server_takes_the_calling_session_from_the_hook_ticket(self):
+        """One app's server shared by two sessions: each call runs as the agent its hook named in a ticket."""
+        from fastmcp import Client
+        from harbor import mcp_server, sessions
+        d = temp_dir()
+        project = make_home(d)["test"]
+        mcp_server._state.clear()
+        mcp_server._state["project"] = project
+        saved = {k: os.environ.get(k) for k in ("HARBOR_AGENT", "HARBOR_HOST")}
+        os.environ.update(HARBOR_AGENT="Codex", HARBOR_HOST="codex")
+
+        async def scenario():
+            async with Client(mcp_server.mcp) as client:
+                sessions.leave(mcp_server.harbor(), "codex", "doing", {"text": "second session"}, "DeepSeek")
+                await client.call_tool("doing", {"text": "second session"})      # the ticket names DeepSeek
+                await client.call_tool("doing", {"text": "first session"})       # no ticket: the server's own
+                status = (await client.call_tool("status", {})).data
+                doing = {a["name"]: a["doing"] for a in status["agents"]}
+                self.assertEqual(doing["DeepSeek"], "second session")
+                self.assertEqual(doing["Codex"], "first session")
+                sessions.leave(mcp_server.harbor(), "codex", "i_am", {"agent": "DeepSeek"}, "DeepSeek")
+                self.assertTrue((await client.call_tool("i_am", {"agent": "DeepSeek"})).data["matches"])
+                self.assertFalse((await client.call_tool("i_am", {"agent": "DeepSeek"})).data["matches"])  # used up
+
+        try:
+            asyncio.run(scenario())
+        finally:
+            for k, v in saved.items():
+                if v is None:
+                    os.environ.pop(k, None)
+                else:
+                    os.environ[k] = v
+            mcp_server._state.pop("h").close()
+            mcp_server._state.clear()
+
     def test_tools_bind_identity_and_round_trip(self):
         from fastmcp import Client
         from fastmcp.exceptions import ToolError