diff --git a/plugins/platforms/a2a/adapter.py b/plugins/platforms/a2a/adapter.py
index 79842c88c6..b546edc841 100644
--- a/plugins/platforms/a2a/adapter.py
+++ b/plugins/platforms/a2a/adapter.py
@@ -74,8 +74,30 @@ def _reply_timeout() -> float:
         return 300.0
 
 
+def _profile_scoped() -> bool:
+    """True when running inside a multiplexed secondary profile's scope.
+
+    Secondary-profile adapters are constructed inside ``_profile_runtime_scope``
+    (secret scope installed + multiplex active) — the same discriminator the
+    Buzz/SimpleX adapters use for this bug class (#98738). The DEFAULT profile
+    under multiplexing runs unscoped: ``os.environ`` holds its own bridge
+    output there and keeps its legacy precedence.
+    """
+    try:
+        from agent.secret_scope import current_secret_scope, is_multiplex_active
+
+        return bool(is_multiplex_active() and current_secret_scope() is not None)
+    except Exception:
+        return False
+
+
 def _default_agent_name() -> str:
-    name = os.getenv("A2A_AGENT_NAME", "").strip()
+    # Scope-aware: inside a secondary multiplex profile, os.environ holds the
+    # DEFAULT profile's bridged A2A_AGENT_NAME — borrowing it would brand a
+    # secondary profile's Agent Card with another profile's identity. There
+    # is no per-profile config.yaml equivalent yet, so a scoped profile just
+    # falls through to the hostname-based default below instead.
+    name = "" if _profile_scoped() else os.getenv("A2A_AGENT_NAME", "").strip()
     if name:
         return name
     try:
@@ -343,7 +365,15 @@ class A2AAdapter(BasePlatformAdapter):
         super().__init__(config=config, platform=platform)
 
         extra = getattr(config, "extra", {}) or {}
-        self.port = int(os.getenv("A2A_PORT") or extra.get("port", _DEFAULT_PORT))
+        # Scope-aware: a secondary multiplex profile must not borrow the
+        # default profile's bridged A2A_PORT (mirrors the Buzz/SimpleX fix
+        # for #98738) — an unconfigured profile falls closed to the module
+        # default port instead. (advertised_toolsets has the same env-leak
+        # shape but is left unscoped here — see the "Scope note" in this
+        # fix's PR description: open PR #98937 is actively rewriting this
+        # field's None-vs-empty-list semantics.)
+        _port_env = None if _profile_scoped() else os.getenv("A2A_PORT")
+        self.port = int(_port_env or extra.get("port", _DEFAULT_PORT))
         self.host = security.resolve_bind_host()
         self.agent_name = _default_agent_name()
         self._advertised_toolsets = [
@@ -502,9 +532,15 @@ class A2AAdapter(BasePlatformAdapter):
             raw = cfg.get("a2a_served_agents") or (cfg.get("a2a") or {}).get("served_agents")
 
         agents: dict[str, dict] = {}
-        default_desc = os.getenv(
-            "A2A_AGENT_DESCRIPTION",
-            "Hermes Agent — a general-purpose agent reachable over A2A.",
+        # Scope-aware for the same reason as port/toolsets above: a secondary
+        # profile must not inherit the default profile's A2A_AGENT_DESCRIPTION.
+        default_desc = (
+            "Hermes Agent — a general-purpose agent reachable over A2A."
+            if _profile_scoped()
+            else os.getenv(
+                "A2A_AGENT_DESCRIPTION",
+                "Hermes Agent — a general-purpose agent reachable over A2A.",
+            )
         )
         agents[""] = {
             "slug": "",
diff --git a/tests/plugins/test_a2a_plugin.py b/tests/plugins/test_a2a_plugin.py
index 346284b277..7e4f933ebd 100644
--- a/tests/plugins/test_a2a_plugin.py
+++ b/tests/plugins/test_a2a_plugin.py
@@ -1618,3 +1618,101 @@ print('fake reply')
         title = con.execute("SELECT title FROM sessions WHERE id='sess-1'").fetchone()[0]
         con.close()
         assert title == "a2a-dev-ctx-unsafe-value"
+
+
+# --------------------------------------------------------------------------
+# Multiplex secondary-profile scope (construction-time config leak)
+# --------------------------------------------------------------------------
+#
+# __init__'s port/advertised-toolsets reads and _load_served_agents's
+# description default all previously read raw A2A_* env vars unconditionally.
+# Under a multiplexed secondary profile, os.environ holds the DEFAULT
+# profile's YAML-to-env bridge output — a secondary profile with its own
+# (different, or absent) A2A config would silently borrow the default
+# profile's port, toolset advertisement, agent name, or Agent Card
+# description. Mirrors the Buzz/SimpleX fix for #98738.
+
+_A2A_ENV_VARS = (
+    "A2A_PORT",
+    "A2A_AGENT_NAME",
+    "A2A_ADVERTISED_TOOLSETS",
+    "A2A_AGENT_DESCRIPTION",
+)
+
+
+@pytest.fixture(autouse=True)
+def _clean_a2a_construction_env(monkeypatch):
+    """Keep the new multiplex tests hermetic regardless of ambient env."""
+    for var in _A2A_ENV_VARS:
+        monkeypatch.delenv(var, raising=False)
+    yield
+
+
+@pytest.fixture
+def multiplex_scope():
+    """Install multiplex + a secondary-profile secret scope; restore after."""
+    tokens = []
+
+    def install(scope=None):
+        from agent.secret_scope import set_multiplex_active, set_secret_scope
+
+        set_multiplex_active(True)
+        tokens.append(set_secret_scope(scope or {}))
+        return tokens[-1]
+
+    yield install
+
+    from agent.secret_scope import reset_secret_scope, set_multiplex_active
+
+    for token in reversed(tokens):
+        reset_secret_scope(token)
+    set_multiplex_active(False)
+
+
+@pytest.fixture
+def default_profile_env(monkeypatch):
+    """The default profile's YAML-to-env bridge output in os.environ."""
+    monkeypatch.setenv("A2A_PORT", "9111")
+    monkeypatch.setenv("A2A_AGENT_NAME", "default-profile-agent")
+    monkeypatch.setenv("A2A_ADVERTISED_TOOLSETS", "default-only-toolset")
+    monkeypatch.setenv("A2A_AGENT_DESCRIPTION", "Default profile's own agent.")
+
+
+class TestMultiplexConstructionScope:
+
+    def test_secondary_profile_never_borrows_default_profile_env(
+        self, multiplex_scope, default_profile_env
+    ):
+        """The secondary profile's own config is authoritative; keys absent
+        from it fall to the module defaults, never to the default profile's
+        bridged A2A_* env values."""
+        from plugins.platforms.a2a.adapter import A2AAdapter, _DEFAULT_PORT
+        from gateway.config import PlatformConfig
+
+        multiplex_scope()
+        assert A2AAdapter(PlatformConfig(enabled=True, extra={"port": 9222})).port == 9222
+
+        adapter = A2AAdapter(PlatformConfig(enabled=True, extra={}))
+        assert adapter.port == _DEFAULT_PORT
+        assert adapter.agent_name != "default-profile-agent"
+        assert adapter._agents[""]["description"] == (
+            "Hermes Agent — a general-purpose agent reachable over A2A."
+        )
+
+    def test_default_profile_unscoped_keeps_env_precedence(
+        self, monkeypatch, default_profile_env
+    ):
+        """Multiplex ON but no scope (the DEFAULT profile constructs
+        unscoped): env is its own bridge output and still wins."""
+        from agent.secret_scope import set_multiplex_active
+        from plugins.platforms.a2a.adapter import A2AAdapter
+        from gateway.config import PlatformConfig
+
+        set_multiplex_active(True)
+        try:
+            adapter = A2AAdapter(PlatformConfig(enabled=True, extra={}))
+        finally:
+            set_multiplex_active(False)
+        assert adapter.port == 9111
+        assert adapter.agent_name == "default-profile-agent"
+        assert adapter._agents[""]["description"] == "Default profile's own agent."