diff --git a/integrations/AGENTS.md b/integrations/AGENTS.md
index 9b85cddb1..221c8206f 100644
--- a/integrations/AGENTS.md
+++ b/integrations/AGENTS.md
@@ -82,6 +82,15 @@ The backend recognizes a fixed list of source values and buckets everything else
 into `OTHERS`. A new value has to land in the platform's `EventSource` enum, so
 do not invent one without that change going in too.
 
+`X-Application` is allowlisted the same way, and this one has a rule of its own:
+**omit the header when you do not know the host.** A value outside the allowlist
+is discarded server-side, so guessing produces an event that claims an
+attribution we do not actually have. The portable bundle is the case that
+matters. It runs in whatever editor a user drops it into, so its build leaves
+`PLATFORM_APPLICATION` empty and `memory_core` sends no header at all, while the
+native bundles each name the host they were generated for. If you add a build
+target, decide which of those two it is.
+
 ## Adding an integration
 
 1. For a native coding-agent host, add `integrations/<name>-plugin/` with `plugin-build.json`, its manifest, and a thin adapter, then generate its shared runtime. Portable clients use the single `mem0-agent-plugin/` package. Independent TypeScript integrations stay self-contained and import shared lifecycle behavior from `agent-plugin-core/typescript/`.
diff --git a/integrations/agent-plugin-core/build/build.py b/integrations/agent-plugin-core/build/build.py
index e675efb02..3059b9b1f 100644
--- a/integrations/agent-plugin-core/build/build.py
+++ b/integrations/agent-plugin-core/build/build.py
@@ -81,15 +81,23 @@ def replace_output(staged: Path, output: Path) -> Path:
     return output
 
 
-def _render_harness_id(host: str) -> str:
+def _render_harness_id(host: str, *, portable: bool = False) -> str:
     """Emit core/_harness_id.py for one host.
 
     Carries both vocabularies from a single definition: the PostHog `source` tag
     and the platform's X-Mem0-Source / X-Application pair. Keeping them together
     is what stops the two from drifting into separate vocabularies for the same
     thing.
+
+    The portable bundle runs in whatever editor a user drops it into, so it does
+    not know its host and must not guess one. HARNESS_ID stays "coding-agent",
+    which is true and useful for grouping in PostHog, but PLATFORM_APPLICATION is
+    left empty: X-Application names a real host app, is checked against an
+    allowlist server-side, and a value that is always discarded is worse than no
+    value -- it reads like an attribution we have and do not.
     """
     tag = host.upper().replace("-", "_") + "_PLUGIN"
+    application = "" if portable else host
     return (
         '"""Generated by integrations/agent-plugin-core/build/build.py. Do not edit."""\n'
         "\n"
@@ -98,8 +106,10 @@ def _render_harness_id(host: str) -> str:
         "\n"
         "# Platform-side vocabulary (mem0_event.source + X-Application). The whole\n"
         "# plugin family is one source; which editor it runs in is the application.\n"
+        "# An empty application means the host is unknown, and memory_core omits\n"
+        "# the header entirely rather than sending a placeholder.\n"
         'PLATFORM_SOURCE = "MEM0_PLUGIN"\n'
-        f'PLATFORM_APPLICATION = "{host}"\n'
+        f'PLATFORM_APPLICATION = "{application}"\n'
     )
 
 
@@ -122,7 +132,7 @@ def _bundle_python(
     # to call telemetry.init(). mcp_server.py and the detached telemetry.py sender
     # never did, which is how MCP searches reported harness=generic and every
     # batch they drained was labelled MEM0_PLUGIN regardless of the real host.
-    (core / "_harness_id.py").write_text(_render_harness_id(host), encoding="utf-8")
+    (core / "_harness_id.py").write_text(_render_harness_id(host, portable=portable), encoding="utf-8")
 
     values = {
         "PLUGIN_ROOT": plugin_root,
diff --git a/integrations/agent-plugin-core/tests/test_build.py b/integrations/agent-plugin-core/tests/test_build.py
index 54b5e5c6a..23295cc38 100644
--- a/integrations/agent-plugin-core/tests/test_build.py
+++ b/integrations/agent-plugin-core/tests/test_build.py
@@ -70,6 +70,38 @@ def test_portable_bundle_is_conformant_and_self_contained(tmp_path: Path) -> Non
     assert not any(path.is_symlink() for path in root.rglob("*"))
 
 
+def _harness_identity(root: Path) -> dict[str, str]:
+    """Read the generated core/_harness_id.py without importing it."""
+    values: dict[str, str] = {}
+    for line in (root / "core" / "_harness_id.py").read_text(encoding="utf-8").splitlines():
+        if "=" in line and not line.lstrip().startswith("#"):
+            name, _, raw = line.partition("=")
+            values[name.strip()] = raw.strip().strip('"')
+    return values
+
+
+def test_the_portable_bundle_declares_no_host_application(tmp_path: Path) -> None:
+    """It runs in whatever editor a user drops it into, so it cannot know the host.
+
+    X-Application is allowlisted server-side. A guessed value is silently dropped
+    there, which is the worst outcome: the wire says we know the host and the
+    stored event says we do not.
+    """
+    identity = _harness_identity(build("mem0-agent-plugin", "portable", tmp_path / "portable"))
+
+    assert identity["PLATFORM_APPLICATION"] == ""
+    # The PostHog-side label is still useful for grouping and stays populated.
+    assert identity["HARNESS_ID"] == "coding-agent"
+    assert identity["PLATFORM_SOURCE"] == "MEM0_PLUGIN"
+
+
+@pytest.mark.parametrize("host", ["claude-code", "cursor", "codex", "kimi", "antigravity"])
+def test_a_native_bundle_names_the_host_it_was_built_for(host: str, tmp_path: Path) -> None:
+    identity = _harness_identity(build(host, "native", tmp_path / host))
+
+    assert identity["PLATFORM_APPLICATION"] == host
+
+
 @pytest.mark.parametrize("host", ["claude-code", "cursor", "codex", "kimi", "antigravity"])
 def test_native_bundle_is_self_contained(host: str, tmp_path: Path) -> None:
     root = build(host, "native", tmp_path / host)
diff --git a/integrations/antigravity-plugin/core/_harness_id.py b/integrations/antigravity-plugin/core/_harness_id.py
index 2c8a515f4..18b7f68ec 100644
--- a/integrations/antigravity-plugin/core/_harness_id.py
+++ b/integrations/antigravity-plugin/core/_harness_id.py
@@ -5,5 +5,7 @@ SOURCE_TAG = "ANTIGRAVITY_PLUGIN"
 
 # Platform-side vocabulary (mem0_event.source + X-Application). The whole
 # plugin family is one source; which editor it runs in is the application.
+# An empty application means the host is unknown, and memory_core omits
+# the header entirely rather than sending a placeholder.
 PLATFORM_SOURCE = "MEM0_PLUGIN"
 PLATFORM_APPLICATION = "antigravity"
diff --git a/integrations/claude-code-plugin/core/_harness_id.py b/integrations/claude-code-plugin/core/_harness_id.py
index 6c3e1ce15..9c4949408 100644
--- a/integrations/claude-code-plugin/core/_harness_id.py
+++ b/integrations/claude-code-plugin/core/_harness_id.py
@@ -5,5 +5,7 @@ SOURCE_TAG = "CLAUDE_CODE_PLUGIN"
 
 # Platform-side vocabulary (mem0_event.source + X-Application). The whole
 # plugin family is one source; which editor it runs in is the application.
+# An empty application means the host is unknown, and memory_core omits
+# the header entirely rather than sending a placeholder.
 PLATFORM_SOURCE = "MEM0_PLUGIN"
 PLATFORM_APPLICATION = "claude-code"
diff --git a/integrations/codex-plugin/core/_harness_id.py b/integrations/codex-plugin/core/_harness_id.py
index 152313a21..47938ee08 100644
--- a/integrations/codex-plugin/core/_harness_id.py
+++ b/integrations/codex-plugin/core/_harness_id.py
@@ -5,5 +5,7 @@ SOURCE_TAG = "CODEX_PLUGIN"
 
 # Platform-side vocabulary (mem0_event.source + X-Application). The whole
 # plugin family is one source; which editor it runs in is the application.
+# An empty application means the host is unknown, and memory_core omits
+# the header entirely rather than sending a placeholder.
 PLATFORM_SOURCE = "MEM0_PLUGIN"
 PLATFORM_APPLICATION = "codex"
diff --git a/integrations/cursor-plugin/core/_harness_id.py b/integrations/cursor-plugin/core/_harness_id.py
index 40241a7f4..0e20bf1ff 100644
--- a/integrations/cursor-plugin/core/_harness_id.py
+++ b/integrations/cursor-plugin/core/_harness_id.py
@@ -5,5 +5,7 @@ SOURCE_TAG = "CURSOR_PLUGIN"
 
 # Platform-side vocabulary (mem0_event.source + X-Application). The whole
 # plugin family is one source; which editor it runs in is the application.
+# An empty application means the host is unknown, and memory_core omits
+# the header entirely rather than sending a placeholder.
 PLATFORM_SOURCE = "MEM0_PLUGIN"
 PLATFORM_APPLICATION = "cursor"
diff --git a/integrations/kimi-plugin/core/_harness_id.py b/integrations/kimi-plugin/core/_harness_id.py
index aa17750b1..83ab061ef 100644
--- a/integrations/kimi-plugin/core/_harness_id.py
+++ b/integrations/kimi-plugin/core/_harness_id.py
@@ -5,5 +5,7 @@ SOURCE_TAG = "KIMI_PLUGIN"
 
 # Platform-side vocabulary (mem0_event.source + X-Application). The whole
 # plugin family is one source; which editor it runs in is the application.
+# An empty application means the host is unknown, and memory_core omits
+# the header entirely rather than sending a placeholder.
 PLATFORM_SOURCE = "MEM0_PLUGIN"
 PLATFORM_APPLICATION = "kimi"
diff --git a/integrations/mem0-agent-plugin/core/_harness_id.py b/integrations/mem0-agent-plugin/core/_harness_id.py
index b0836d6de..3efd000f8 100644
--- a/integrations/mem0-agent-plugin/core/_harness_id.py
+++ b/integrations/mem0-agent-plugin/core/_harness_id.py
@@ -5,5 +5,7 @@ SOURCE_TAG = "CODING_AGENT_PLUGIN"
 
 # Platform-side vocabulary (mem0_event.source + X-Application). The whole
 # plugin family is one source; which editor it runs in is the application.
+# An empty application means the host is unknown, and memory_core omits
+# the header entirely rather than sending a placeholder.
 PLATFORM_SOURCE = "MEM0_PLUGIN"
-PLATFORM_APPLICATION = "coding-agent"
+PLATFORM_APPLICATION = ""