diff --git a/integrations/agent-plugin-core/python/telemetry.py b/integrations/agent-plugin-core/python/telemetry.py
index 239836604..2cb1056e0 100644
--- a/integrations/agent-plugin-core/python/telemetry.py
+++ b/integrations/agent-plugin-core/python/telemetry.py
@@ -116,36 +116,49 @@ def _install_salt() -> str:
       keys off that file, so recording an event would silently suppress the
       install event.
 
-    On a read-only or full data directory the fallback is derived from the data
-    directory path: stable for the machine rather than random per call, so the
-    failure mode is a weaker salt and not unbounded cardinality in PostHog.
+    Published atomically, and there is deliberately no derived fallback. Creating
+    the file with O_CREAT|O_EXCL and then writing into it leaves a window where
+    the file exists and is empty, and a concurrent hook that reads it in that
+    window gets nothing. Falling back to a digest of the path would hand that
+    process a salt an attacker can compute, memoized for its whole run, which is
+    the privacy control this function exists to provide silently turning itself
+    off under load. The salt is written to a private temp file first and linked
+    into place, so the name either does not exist or already has the full value.
+
+    Returns "" when it genuinely cannot persist. Callers omit the hash entirely
+    rather than emit an unsalted one.
     """
     global _salt_cache
     if _salt_cache:
         return _salt_cache
 
     path = _salt_path()
+    temporary = path.with_name(f"{path.name}.{os.getpid()}.tmp")
     try:
         path.parent.mkdir(parents=True, exist_ok=True)
-        handle = os.open(path, os.O_CREAT | os.O_EXCL | os.O_WRONLY, 0o600)
+        handle = os.open(temporary, os.O_CREAT | os.O_EXCL | os.O_WRONLY, 0o600)
+        with os.fdopen(handle, "w", encoding="utf-8") as stream:
+            stream.write(uuid.uuid4().hex)
+            stream.flush()
+            os.fsync(stream.fileno())
         try:
-            with os.fdopen(handle, "w", encoding="utf-8") as stream:
-                stream.write(uuid.uuid4().hex)
+            # Atomic claim: fails if another process already published one.
+            # os.link rather than replace, which would clobber theirs.
+            os.link(temporary, path)
+        except FileExistsError:
+            pass
+    except OSError:
+        pass
+    finally:
+        try:
+            temporary.unlink()
         except OSError:
             pass
-    except FileExistsError:
-        pass
-    except OSError:
-        # Cannot persist. Stable-per-machine beats random-per-call.
-        _salt_cache = hashlib.sha256(str(path).encode("utf-8")).hexdigest()
-        return _salt_cache
 
     try:
         _salt_cache = path.read_text(encoding="utf-8").strip()
     except OSError:
         _salt_cache = ""
-    if not _salt_cache:
-        _salt_cache = hashlib.sha256(str(path).encode("utf-8")).hexdigest()
     return _salt_cache
 
 
@@ -158,10 +171,17 @@ def _scoped_digest(value: str, length: int = 16) -> str:
     privacy control without the salt. Salting per install keeps every
     within-account join the analytics actually use and gives up only
     cross-machine joins on the same repository, which nothing computes.
+
+    Returns "" when there is no salt, so record() omits the property. An
+    unsalted digest over this input space is close to plaintext, and emitting one
+    under a name that implies it is hashed is worse than sending nothing.
     """
     if not value:
         return ""
-    return hashlib.sha256(f"{_install_salt()}:{value}".encode("utf-8")).hexdigest()[:length]
+    salt = _install_salt()
+    if not salt:
+        return ""
+    return hashlib.sha256(f"{salt}:{value}".encode("utf-8")).hexdigest()[:length]
 
 
 def _safe_value(value: Any) -> Any:
@@ -252,10 +272,17 @@ def record(
             os=sys.platform,
             python_version=platform.python_version(),
         )
+        # Assigned only when the digest is real. _scoped_digest returns "" when
+        # the salt could not be persisted, and an empty property is worse than an
+        # absent one: it survives the None filter below and reads as a value.
         if repo is not None:
-            properties["repo_hash"] = _scoped_digest(getattr(repo, "identity", ""))
+            repo_hash = _scoped_digest(getattr(repo, "identity", ""))
+            if repo_hash:
+                properties["repo_hash"] = repo_hash
         if session_id:
-            properties["session_hash"] = _scoped_digest(session_id)
+            session_hash = _scoped_digest(session_id)
+            if session_hash:
+                properties["session_hash"] = session_hash
         line = json.dumps(
             {
                 "event": f"{EVENT_PREFIX}.{event}",
diff --git a/integrations/antigravity-plugin/core/telemetry.py b/integrations/antigravity-plugin/core/telemetry.py
index 239836604..2cb1056e0 100644
--- a/integrations/antigravity-plugin/core/telemetry.py
+++ b/integrations/antigravity-plugin/core/telemetry.py
@@ -116,36 +116,49 @@ def _install_salt() -> str:
       keys off that file, so recording an event would silently suppress the
       install event.
 
-    On a read-only or full data directory the fallback is derived from the data
-    directory path: stable for the machine rather than random per call, so the
-    failure mode is a weaker salt and not unbounded cardinality in PostHog.
+    Published atomically, and there is deliberately no derived fallback. Creating
+    the file with O_CREAT|O_EXCL and then writing into it leaves a window where
+    the file exists and is empty, and a concurrent hook that reads it in that
+    window gets nothing. Falling back to a digest of the path would hand that
+    process a salt an attacker can compute, memoized for its whole run, which is
+    the privacy control this function exists to provide silently turning itself
+    off under load. The salt is written to a private temp file first and linked
+    into place, so the name either does not exist or already has the full value.
+
+    Returns "" when it genuinely cannot persist. Callers omit the hash entirely
+    rather than emit an unsalted one.
     """
     global _salt_cache
     if _salt_cache:
         return _salt_cache
 
     path = _salt_path()
+    temporary = path.with_name(f"{path.name}.{os.getpid()}.tmp")
     try:
         path.parent.mkdir(parents=True, exist_ok=True)
-        handle = os.open(path, os.O_CREAT | os.O_EXCL | os.O_WRONLY, 0o600)
+        handle = os.open(temporary, os.O_CREAT | os.O_EXCL | os.O_WRONLY, 0o600)
+        with os.fdopen(handle, "w", encoding="utf-8") as stream:
+            stream.write(uuid.uuid4().hex)
+            stream.flush()
+            os.fsync(stream.fileno())
         try:
-            with os.fdopen(handle, "w", encoding="utf-8") as stream:
-                stream.write(uuid.uuid4().hex)
+            # Atomic claim: fails if another process already published one.
+            # os.link rather than replace, which would clobber theirs.
+            os.link(temporary, path)
+        except FileExistsError:
+            pass
+    except OSError:
+        pass
+    finally:
+        try:
+            temporary.unlink()
         except OSError:
             pass
-    except FileExistsError:
-        pass
-    except OSError:
-        # Cannot persist. Stable-per-machine beats random-per-call.
-        _salt_cache = hashlib.sha256(str(path).encode("utf-8")).hexdigest()
-        return _salt_cache
 
     try:
         _salt_cache = path.read_text(encoding="utf-8").strip()
     except OSError:
         _salt_cache = ""
-    if not _salt_cache:
-        _salt_cache = hashlib.sha256(str(path).encode("utf-8")).hexdigest()
     return _salt_cache
 
 
@@ -158,10 +171,17 @@ def _scoped_digest(value: str, length: int = 16) -> str:
     privacy control without the salt. Salting per install keeps every
     within-account join the analytics actually use and gives up only
     cross-machine joins on the same repository, which nothing computes.
+
+    Returns "" when there is no salt, so record() omits the property. An
+    unsalted digest over this input space is close to plaintext, and emitting one
+    under a name that implies it is hashed is worse than sending nothing.
     """
     if not value:
         return ""
-    return hashlib.sha256(f"{_install_salt()}:{value}".encode("utf-8")).hexdigest()[:length]
+    salt = _install_salt()
+    if not salt:
+        return ""
+    return hashlib.sha256(f"{salt}:{value}".encode("utf-8")).hexdigest()[:length]
 
 
 def _safe_value(value: Any) -> Any:
@@ -252,10 +272,17 @@ def record(
             os=sys.platform,
             python_version=platform.python_version(),
         )
+        # Assigned only when the digest is real. _scoped_digest returns "" when
+        # the salt could not be persisted, and an empty property is worse than an
+        # absent one: it survives the None filter below and reads as a value.
         if repo is not None:
-            properties["repo_hash"] = _scoped_digest(getattr(repo, "identity", ""))
+            repo_hash = _scoped_digest(getattr(repo, "identity", ""))
+            if repo_hash:
+                properties["repo_hash"] = repo_hash
         if session_id:
-            properties["session_hash"] = _scoped_digest(session_id)
+            session_hash = _scoped_digest(session_id)
+            if session_hash:
+                properties["session_hash"] = session_hash
         line = json.dumps(
             {
                 "event": f"{EVENT_PREFIX}.{event}",
diff --git a/integrations/claude-code-plugin/core/telemetry.py b/integrations/claude-code-plugin/core/telemetry.py
index 239836604..2cb1056e0 100644
--- a/integrations/claude-code-plugin/core/telemetry.py
+++ b/integrations/claude-code-plugin/core/telemetry.py
@@ -116,36 +116,49 @@ def _install_salt() -> str:
       keys off that file, so recording an event would silently suppress the
       install event.
 
-    On a read-only or full data directory the fallback is derived from the data
-    directory path: stable for the machine rather than random per call, so the
-    failure mode is a weaker salt and not unbounded cardinality in PostHog.
+    Published atomically, and there is deliberately no derived fallback. Creating
+    the file with O_CREAT|O_EXCL and then writing into it leaves a window where
+    the file exists and is empty, and a concurrent hook that reads it in that
+    window gets nothing. Falling back to a digest of the path would hand that
+    process a salt an attacker can compute, memoized for its whole run, which is
+    the privacy control this function exists to provide silently turning itself
+    off under load. The salt is written to a private temp file first and linked
+    into place, so the name either does not exist or already has the full value.
+
+    Returns "" when it genuinely cannot persist. Callers omit the hash entirely
+    rather than emit an unsalted one.
     """
     global _salt_cache
     if _salt_cache:
         return _salt_cache
 
     path = _salt_path()
+    temporary = path.with_name(f"{path.name}.{os.getpid()}.tmp")
     try:
         path.parent.mkdir(parents=True, exist_ok=True)
-        handle = os.open(path, os.O_CREAT | os.O_EXCL | os.O_WRONLY, 0o600)
+        handle = os.open(temporary, os.O_CREAT | os.O_EXCL | os.O_WRONLY, 0o600)
+        with os.fdopen(handle, "w", encoding="utf-8") as stream:
+            stream.write(uuid.uuid4().hex)
+            stream.flush()
+            os.fsync(stream.fileno())
         try:
-            with os.fdopen(handle, "w", encoding="utf-8") as stream:
-                stream.write(uuid.uuid4().hex)
+            # Atomic claim: fails if another process already published one.
+            # os.link rather than replace, which would clobber theirs.
+            os.link(temporary, path)
+        except FileExistsError:
+            pass
+    except OSError:
+        pass
+    finally:
+        try:
+            temporary.unlink()
         except OSError:
             pass
-    except FileExistsError:
-        pass
-    except OSError:
-        # Cannot persist. Stable-per-machine beats random-per-call.
-        _salt_cache = hashlib.sha256(str(path).encode("utf-8")).hexdigest()
-        return _salt_cache
 
     try:
         _salt_cache = path.read_text(encoding="utf-8").strip()
     except OSError:
         _salt_cache = ""
-    if not _salt_cache:
-        _salt_cache = hashlib.sha256(str(path).encode("utf-8")).hexdigest()
     return _salt_cache
 
 
@@ -158,10 +171,17 @@ def _scoped_digest(value: str, length: int = 16) -> str:
     privacy control without the salt. Salting per install keeps every
     within-account join the analytics actually use and gives up only
     cross-machine joins on the same repository, which nothing computes.
+
+    Returns "" when there is no salt, so record() omits the property. An
+    unsalted digest over this input space is close to plaintext, and emitting one
+    under a name that implies it is hashed is worse than sending nothing.
     """
     if not value:
         return ""
-    return hashlib.sha256(f"{_install_salt()}:{value}".encode("utf-8")).hexdigest()[:length]
+    salt = _install_salt()
+    if not salt:
+        return ""
+    return hashlib.sha256(f"{salt}:{value}".encode("utf-8")).hexdigest()[:length]
 
 
 def _safe_value(value: Any) -> Any:
@@ -252,10 +272,17 @@ def record(
             os=sys.platform,
             python_version=platform.python_version(),
         )
+        # Assigned only when the digest is real. _scoped_digest returns "" when
+        # the salt could not be persisted, and an empty property is worse than an
+        # absent one: it survives the None filter below and reads as a value.
         if repo is not None:
-            properties["repo_hash"] = _scoped_digest(getattr(repo, "identity", ""))
+            repo_hash = _scoped_digest(getattr(repo, "identity", ""))
+            if repo_hash:
+                properties["repo_hash"] = repo_hash
         if session_id:
-            properties["session_hash"] = _scoped_digest(session_id)
+            session_hash = _scoped_digest(session_id)
+            if session_hash:
+                properties["session_hash"] = session_hash
         line = json.dumps(
             {
                 "event": f"{EVENT_PREFIX}.{event}",
diff --git a/integrations/claude-code-plugin/tests/test_telemetry.py b/integrations/claude-code-plugin/tests/test_telemetry.py
index eaa741ac5..b816b629e 100644
--- a/integrations/claude-code-plugin/tests/test_telemetry.py
+++ b/integrations/claude-code-plugin/tests/test_telemetry.py
@@ -309,14 +309,59 @@ def test_salt_does_not_touch_the_identity_file(isolated_env):
     assert not telemetry._identity_path().exists()
 
 
-def test_salt_is_stable_when_it_cannot_be_persisted(isolated_env, monkeypatch):
-    """A read-only data dir must degrade to a weaker salt, not to random-per-call.
+def test_no_salt_means_no_hash_rather_than_an_unsalted_one(isolated_env, monkeypatch):
+    """A read-only data dir drops the property; it must not emit a weak digest.
 
-    Random per call is unbounded cardinality in PostHog, which is worse than no
-    salt at all.
+    The previous fallback was a digest of the salt file's own path, which an
+    attacker can compute, memoized for the whole process. A property named
+    repo_hash carrying an effectively unsalted digest is worse than no property:
+    it reads as protected and is not.
     """
     telemetry._salt_cache = ""
     monkeypatch.setattr(telemetry.os, "open", lambda *a, **k: (_ for _ in ()).throw(OSError("read-only")))
-    first = telemetry._install_salt()
+
+    assert telemetry._install_salt() == ""
+    assert telemetry._scoped_digest("git@github.com:acme/secret.git") == ""
+
+
+def test_a_half_written_salt_is_never_visible_to_another_process(isolated_env, monkeypatch):
+    """The window this closes: file created, value not yet written.
+
+    O_CREAT|O_EXCL then write leaves the name present and empty in between. A
+    hook reading it there used to get "", fall back to the path digest and cache
+    that for its whole run, so the same repo hashed two ways depending on timing.
+    Publishing by link means the name either does not exist or is complete.
+    """
     telemetry._salt_cache = ""
-    assert telemetry._install_salt() == first
+    salt_path = telemetry._salt_path()
+    observed = []
+
+    real_link = telemetry.os.link
+
+    def observing_link(source, target):
+        # Stand where the racing reader stands: after the temp file is written,
+        # before the real name exists.
+        observed.append(salt_path.exists())
+        return real_link(source, target)
+
+    monkeypatch.setattr(telemetry.os, "link", observing_link)
+    salt = telemetry._install_salt()
+
+    assert observed == [False], "the salt name existed before it held a value"
+    assert len(salt) == 32
+    assert salt_path.read_text(encoding="utf-8").strip() == salt
+
+
+def test_a_concurrent_writer_does_not_clobber_the_published_salt(isolated_env):
+    """Second process to finish must adopt the first one's salt, not replace it.
+
+    os.link rather than os.replace is what makes losing the race harmless.
+    """
+    telemetry._salt_cache = ""
+    first = telemetry._install_salt()
+
+    telemetry._salt_cache = ""
+    second = telemetry._install_salt()
+
+    assert second == first
+    assert not list(telemetry._salt_path().parent.glob("telemetry-salt.*.tmp")), "temp file left behind"
diff --git a/integrations/codex-plugin/core/telemetry.py b/integrations/codex-plugin/core/telemetry.py
index 239836604..2cb1056e0 100644
--- a/integrations/codex-plugin/core/telemetry.py
+++ b/integrations/codex-plugin/core/telemetry.py
@@ -116,36 +116,49 @@ def _install_salt() -> str:
       keys off that file, so recording an event would silently suppress the
       install event.
 
-    On a read-only or full data directory the fallback is derived from the data
-    directory path: stable for the machine rather than random per call, so the
-    failure mode is a weaker salt and not unbounded cardinality in PostHog.
+    Published atomically, and there is deliberately no derived fallback. Creating
+    the file with O_CREAT|O_EXCL and then writing into it leaves a window where
+    the file exists and is empty, and a concurrent hook that reads it in that
+    window gets nothing. Falling back to a digest of the path would hand that
+    process a salt an attacker can compute, memoized for its whole run, which is
+    the privacy control this function exists to provide silently turning itself
+    off under load. The salt is written to a private temp file first and linked
+    into place, so the name either does not exist or already has the full value.
+
+    Returns "" when it genuinely cannot persist. Callers omit the hash entirely
+    rather than emit an unsalted one.
     """
     global _salt_cache
     if _salt_cache:
         return _salt_cache
 
     path = _salt_path()
+    temporary = path.with_name(f"{path.name}.{os.getpid()}.tmp")
     try:
         path.parent.mkdir(parents=True, exist_ok=True)
-        handle = os.open(path, os.O_CREAT | os.O_EXCL | os.O_WRONLY, 0o600)
+        handle = os.open(temporary, os.O_CREAT | os.O_EXCL | os.O_WRONLY, 0o600)
+        with os.fdopen(handle, "w", encoding="utf-8") as stream:
+            stream.write(uuid.uuid4().hex)
+            stream.flush()
+            os.fsync(stream.fileno())
         try:
-            with os.fdopen(handle, "w", encoding="utf-8") as stream:
-                stream.write(uuid.uuid4().hex)
+            # Atomic claim: fails if another process already published one.
+            # os.link rather than replace, which would clobber theirs.
+            os.link(temporary, path)
+        except FileExistsError:
+            pass
+    except OSError:
+        pass
+    finally:
+        try:
+            temporary.unlink()
         except OSError:
             pass
-    except FileExistsError:
-        pass
-    except OSError:
-        # Cannot persist. Stable-per-machine beats random-per-call.
-        _salt_cache = hashlib.sha256(str(path).encode("utf-8")).hexdigest()
-        return _salt_cache
 
     try:
         _salt_cache = path.read_text(encoding="utf-8").strip()
     except OSError:
         _salt_cache = ""
-    if not _salt_cache:
-        _salt_cache = hashlib.sha256(str(path).encode("utf-8")).hexdigest()
     return _salt_cache
 
 
@@ -158,10 +171,17 @@ def _scoped_digest(value: str, length: int = 16) -> str:
     privacy control without the salt. Salting per install keeps every
     within-account join the analytics actually use and gives up only
     cross-machine joins on the same repository, which nothing computes.
+
+    Returns "" when there is no salt, so record() omits the property. An
+    unsalted digest over this input space is close to plaintext, and emitting one
+    under a name that implies it is hashed is worse than sending nothing.
     """
     if not value:
         return ""
-    return hashlib.sha256(f"{_install_salt()}:{value}".encode("utf-8")).hexdigest()[:length]
+    salt = _install_salt()
+    if not salt:
+        return ""
+    return hashlib.sha256(f"{salt}:{value}".encode("utf-8")).hexdigest()[:length]
 
 
 def _safe_value(value: Any) -> Any:
@@ -252,10 +272,17 @@ def record(
             os=sys.platform,
             python_version=platform.python_version(),
         )
+        # Assigned only when the digest is real. _scoped_digest returns "" when
+        # the salt could not be persisted, and an empty property is worse than an
+        # absent one: it survives the None filter below and reads as a value.
         if repo is not None:
-            properties["repo_hash"] = _scoped_digest(getattr(repo, "identity", ""))
+            repo_hash = _scoped_digest(getattr(repo, "identity", ""))
+            if repo_hash:
+                properties["repo_hash"] = repo_hash
         if session_id:
-            properties["session_hash"] = _scoped_digest(session_id)
+            session_hash = _scoped_digest(session_id)
+            if session_hash:
+                properties["session_hash"] = session_hash
         line = json.dumps(
             {
                 "event": f"{EVENT_PREFIX}.{event}",
diff --git a/integrations/cursor-plugin/core/telemetry.py b/integrations/cursor-plugin/core/telemetry.py
index 239836604..2cb1056e0 100644
--- a/integrations/cursor-plugin/core/telemetry.py
+++ b/integrations/cursor-plugin/core/telemetry.py
@@ -116,36 +116,49 @@ def _install_salt() -> str:
       keys off that file, so recording an event would silently suppress the
       install event.
 
-    On a read-only or full data directory the fallback is derived from the data
-    directory path: stable for the machine rather than random per call, so the
-    failure mode is a weaker salt and not unbounded cardinality in PostHog.
+    Published atomically, and there is deliberately no derived fallback. Creating
+    the file with O_CREAT|O_EXCL and then writing into it leaves a window where
+    the file exists and is empty, and a concurrent hook that reads it in that
+    window gets nothing. Falling back to a digest of the path would hand that
+    process a salt an attacker can compute, memoized for its whole run, which is
+    the privacy control this function exists to provide silently turning itself
+    off under load. The salt is written to a private temp file first and linked
+    into place, so the name either does not exist or already has the full value.
+
+    Returns "" when it genuinely cannot persist. Callers omit the hash entirely
+    rather than emit an unsalted one.
     """
     global _salt_cache
     if _salt_cache:
         return _salt_cache
 
     path = _salt_path()
+    temporary = path.with_name(f"{path.name}.{os.getpid()}.tmp")
     try:
         path.parent.mkdir(parents=True, exist_ok=True)
-        handle = os.open(path, os.O_CREAT | os.O_EXCL | os.O_WRONLY, 0o600)
+        handle = os.open(temporary, os.O_CREAT | os.O_EXCL | os.O_WRONLY, 0o600)
+        with os.fdopen(handle, "w", encoding="utf-8") as stream:
+            stream.write(uuid.uuid4().hex)
+            stream.flush()
+            os.fsync(stream.fileno())
         try:
-            with os.fdopen(handle, "w", encoding="utf-8") as stream:
-                stream.write(uuid.uuid4().hex)
+            # Atomic claim: fails if another process already published one.
+            # os.link rather than replace, which would clobber theirs.
+            os.link(temporary, path)
+        except FileExistsError:
+            pass
+    except OSError:
+        pass
+    finally:
+        try:
+            temporary.unlink()
         except OSError:
             pass
-    except FileExistsError:
-        pass
-    except OSError:
-        # Cannot persist. Stable-per-machine beats random-per-call.
-        _salt_cache = hashlib.sha256(str(path).encode("utf-8")).hexdigest()
-        return _salt_cache
 
     try:
         _salt_cache = path.read_text(encoding="utf-8").strip()
     except OSError:
         _salt_cache = ""
-    if not _salt_cache:
-        _salt_cache = hashlib.sha256(str(path).encode("utf-8")).hexdigest()
     return _salt_cache
 
 
@@ -158,10 +171,17 @@ def _scoped_digest(value: str, length: int = 16) -> str:
     privacy control without the salt. Salting per install keeps every
     within-account join the analytics actually use and gives up only
     cross-machine joins on the same repository, which nothing computes.
+
+    Returns "" when there is no salt, so record() omits the property. An
+    unsalted digest over this input space is close to plaintext, and emitting one
+    under a name that implies it is hashed is worse than sending nothing.
     """
     if not value:
         return ""
-    return hashlib.sha256(f"{_install_salt()}:{value}".encode("utf-8")).hexdigest()[:length]
+    salt = _install_salt()
+    if not salt:
+        return ""
+    return hashlib.sha256(f"{salt}:{value}".encode("utf-8")).hexdigest()[:length]
 
 
 def _safe_value(value: Any) -> Any:
@@ -252,10 +272,17 @@ def record(
             os=sys.platform,
             python_version=platform.python_version(),
         )
+        # Assigned only when the digest is real. _scoped_digest returns "" when
+        # the salt could not be persisted, and an empty property is worse than an
+        # absent one: it survives the None filter below and reads as a value.
         if repo is not None:
-            properties["repo_hash"] = _scoped_digest(getattr(repo, "identity", ""))
+            repo_hash = _scoped_digest(getattr(repo, "identity", ""))
+            if repo_hash:
+                properties["repo_hash"] = repo_hash
         if session_id:
-            properties["session_hash"] = _scoped_digest(session_id)
+            session_hash = _scoped_digest(session_id)
+            if session_hash:
+                properties["session_hash"] = session_hash
         line = json.dumps(
             {
                 "event": f"{EVENT_PREFIX}.{event}",
diff --git a/integrations/kimi-plugin/core/telemetry.py b/integrations/kimi-plugin/core/telemetry.py
index 239836604..2cb1056e0 100644
--- a/integrations/kimi-plugin/core/telemetry.py
+++ b/integrations/kimi-plugin/core/telemetry.py
@@ -116,36 +116,49 @@ def _install_salt() -> str:
       keys off that file, so recording an event would silently suppress the
       install event.
 
-    On a read-only or full data directory the fallback is derived from the data
-    directory path: stable for the machine rather than random per call, so the
-    failure mode is a weaker salt and not unbounded cardinality in PostHog.
+    Published atomically, and there is deliberately no derived fallback. Creating
+    the file with O_CREAT|O_EXCL and then writing into it leaves a window where
+    the file exists and is empty, and a concurrent hook that reads it in that
+    window gets nothing. Falling back to a digest of the path would hand that
+    process a salt an attacker can compute, memoized for its whole run, which is
+    the privacy control this function exists to provide silently turning itself
+    off under load. The salt is written to a private temp file first and linked
+    into place, so the name either does not exist or already has the full value.
+
+    Returns "" when it genuinely cannot persist. Callers omit the hash entirely
+    rather than emit an unsalted one.
     """
     global _salt_cache
     if _salt_cache:
         return _salt_cache
 
     path = _salt_path()
+    temporary = path.with_name(f"{path.name}.{os.getpid()}.tmp")
     try:
         path.parent.mkdir(parents=True, exist_ok=True)
-        handle = os.open(path, os.O_CREAT | os.O_EXCL | os.O_WRONLY, 0o600)
+        handle = os.open(temporary, os.O_CREAT | os.O_EXCL | os.O_WRONLY, 0o600)
+        with os.fdopen(handle, "w", encoding="utf-8") as stream:
+            stream.write(uuid.uuid4().hex)
+            stream.flush()
+            os.fsync(stream.fileno())
         try:
-            with os.fdopen(handle, "w", encoding="utf-8") as stream:
-                stream.write(uuid.uuid4().hex)
+            # Atomic claim: fails if another process already published one.
+            # os.link rather than replace, which would clobber theirs.
+            os.link(temporary, path)
+        except FileExistsError:
+            pass
+    except OSError:
+        pass
+    finally:
+        try:
+            temporary.unlink()
         except OSError:
             pass
-    except FileExistsError:
-        pass
-    except OSError:
-        # Cannot persist. Stable-per-machine beats random-per-call.
-        _salt_cache = hashlib.sha256(str(path).encode("utf-8")).hexdigest()
-        return _salt_cache
 
     try:
         _salt_cache = path.read_text(encoding="utf-8").strip()
     except OSError:
         _salt_cache = ""
-    if not _salt_cache:
-        _salt_cache = hashlib.sha256(str(path).encode("utf-8")).hexdigest()
     return _salt_cache
 
 
@@ -158,10 +171,17 @@ def _scoped_digest(value: str, length: int = 16) -> str:
     privacy control without the salt. Salting per install keeps every
     within-account join the analytics actually use and gives up only
     cross-machine joins on the same repository, which nothing computes.
+
+    Returns "" when there is no salt, so record() omits the property. An
+    unsalted digest over this input space is close to plaintext, and emitting one
+    under a name that implies it is hashed is worse than sending nothing.
     """
     if not value:
         return ""
-    return hashlib.sha256(f"{_install_salt()}:{value}".encode("utf-8")).hexdigest()[:length]
+    salt = _install_salt()
+    if not salt:
+        return ""
+    return hashlib.sha256(f"{salt}:{value}".encode("utf-8")).hexdigest()[:length]
 
 
 def _safe_value(value: Any) -> Any:
@@ -252,10 +272,17 @@ def record(
             os=sys.platform,
             python_version=platform.python_version(),
         )
+        # Assigned only when the digest is real. _scoped_digest returns "" when
+        # the salt could not be persisted, and an empty property is worse than an
+        # absent one: it survives the None filter below and reads as a value.
         if repo is not None:
-            properties["repo_hash"] = _scoped_digest(getattr(repo, "identity", ""))
+            repo_hash = _scoped_digest(getattr(repo, "identity", ""))
+            if repo_hash:
+                properties["repo_hash"] = repo_hash
         if session_id:
-            properties["session_hash"] = _scoped_digest(session_id)
+            session_hash = _scoped_digest(session_id)
+            if session_hash:
+                properties["session_hash"] = session_hash
         line = json.dumps(
             {
                 "event": f"{EVENT_PREFIX}.{event}",
diff --git a/integrations/mem0-agent-plugin/core/telemetry.py b/integrations/mem0-agent-plugin/core/telemetry.py
index 239836604..2cb1056e0 100644
--- a/integrations/mem0-agent-plugin/core/telemetry.py
+++ b/integrations/mem0-agent-plugin/core/telemetry.py
@@ -116,36 +116,49 @@ def _install_salt() -> str:
       keys off that file, so recording an event would silently suppress the
       install event.
 
-    On a read-only or full data directory the fallback is derived from the data
-    directory path: stable for the machine rather than random per call, so the
-    failure mode is a weaker salt and not unbounded cardinality in PostHog.
+    Published atomically, and there is deliberately no derived fallback. Creating
+    the file with O_CREAT|O_EXCL and then writing into it leaves a window where
+    the file exists and is empty, and a concurrent hook that reads it in that
+    window gets nothing. Falling back to a digest of the path would hand that
+    process a salt an attacker can compute, memoized for its whole run, which is
+    the privacy control this function exists to provide silently turning itself
+    off under load. The salt is written to a private temp file first and linked
+    into place, so the name either does not exist or already has the full value.
+
+    Returns "" when it genuinely cannot persist. Callers omit the hash entirely
+    rather than emit an unsalted one.
     """
     global _salt_cache
     if _salt_cache:
         return _salt_cache
 
     path = _salt_path()
+    temporary = path.with_name(f"{path.name}.{os.getpid()}.tmp")
     try:
         path.parent.mkdir(parents=True, exist_ok=True)
-        handle = os.open(path, os.O_CREAT | os.O_EXCL | os.O_WRONLY, 0o600)
+        handle = os.open(temporary, os.O_CREAT | os.O_EXCL | os.O_WRONLY, 0o600)
+        with os.fdopen(handle, "w", encoding="utf-8") as stream:
+            stream.write(uuid.uuid4().hex)
+            stream.flush()
+            os.fsync(stream.fileno())
         try:
-            with os.fdopen(handle, "w", encoding="utf-8") as stream:
-                stream.write(uuid.uuid4().hex)
+            # Atomic claim: fails if another process already published one.
+            # os.link rather than replace, which would clobber theirs.
+            os.link(temporary, path)
+        except FileExistsError:
+            pass
+    except OSError:
+        pass
+    finally:
+        try:
+            temporary.unlink()
         except OSError:
             pass
-    except FileExistsError:
-        pass
-    except OSError:
-        # Cannot persist. Stable-per-machine beats random-per-call.
-        _salt_cache = hashlib.sha256(str(path).encode("utf-8")).hexdigest()
-        return _salt_cache
 
     try:
         _salt_cache = path.read_text(encoding="utf-8").strip()
     except OSError:
         _salt_cache = ""
-    if not _salt_cache:
-        _salt_cache = hashlib.sha256(str(path).encode("utf-8")).hexdigest()
     return _salt_cache
 
 
@@ -158,10 +171,17 @@ def _scoped_digest(value: str, length: int = 16) -> str:
     privacy control without the salt. Salting per install keeps every
     within-account join the analytics actually use and gives up only
     cross-machine joins on the same repository, which nothing computes.
+
+    Returns "" when there is no salt, so record() omits the property. An
+    unsalted digest over this input space is close to plaintext, and emitting one
+    under a name that implies it is hashed is worse than sending nothing.
     """
     if not value:
         return ""
-    return hashlib.sha256(f"{_install_salt()}:{value}".encode("utf-8")).hexdigest()[:length]
+    salt = _install_salt()
+    if not salt:
+        return ""
+    return hashlib.sha256(f"{salt}:{value}".encode("utf-8")).hexdigest()[:length]
 
 
 def _safe_value(value: Any) -> Any:
@@ -252,10 +272,17 @@ def record(
             os=sys.platform,
             python_version=platform.python_version(),
         )
+        # Assigned only when the digest is real. _scoped_digest returns "" when
+        # the salt could not be persisted, and an empty property is worse than an
+        # absent one: it survives the None filter below and reads as a value.
         if repo is not None:
-            properties["repo_hash"] = _scoped_digest(getattr(repo, "identity", ""))
+            repo_hash = _scoped_digest(getattr(repo, "identity", ""))
+            if repo_hash:
+                properties["repo_hash"] = repo_hash
         if session_id:
-            properties["session_hash"] = _scoped_digest(session_id)
+            session_hash = _scoped_digest(session_id)
+            if session_hash:
+                properties["session_hash"] = session_hash
         line = json.dumps(
             {
                 "event": f"{EVENT_PREFIX}.{event}",