diff --git a/integrations/agent-plugin-core/python/telemetry.py b/integrations/agent-plugin-core/python/telemetry.py
index 55ee7c907..fa26cc9a6 100644
--- a/integrations/agent-plugin-core/python/telemetry.py
+++ b/integrations/agent-plugin-core/python/telemetry.py
@@ -313,9 +313,18 @@ def _claim_name(attempt: int = 0) -> str:
 
 
 def _claim_attempt(claim: Path) -> int:
-    """Attempts recorded in a claim filename; 0 for the pre-attempt-count shape."""
+    """Attempts recorded in a claim filename; 0 for the pre-attempt-count shape.
+
+    Anchored on field position, not on a leading "a": the legacy shape is
+    ``telemetry-<pid>-<hex>.sending`` and a hex id such as ``a1234567`` would
+    otherwise parse as attempt 1234567 and be discarded unsent on the first
+    flush after an upgrade.
+    """
     stem = claim.name[: -len(".sending")] if claim.name.endswith(".sending") else claim.name
-    tail = stem.rsplit("-", 1)[-1]
+    parts = stem.split("-")
+    if len(parts) != 4:
+        return 0
+    tail = parts[3]
     if tail.startswith("a") and tail[1:].isdigit():
         return int(tail[1:])
     return 0
@@ -349,6 +358,21 @@ def _claim_spool() -> Path | None:
     return _claim_parked(directory)
 
 
+def _sweep_debris(directory: Path) -> None:
+    """Remove temp files orphaned by a crash between write and rename.
+
+    Neither glob in this module matches *.partial, so nothing else would ever
+    clean them up.
+    """
+    now = time.time()
+    for debris in directory.glob("telemetry-*.partial"):
+        try:
+            if now - debris.stat().st_mtime > CLAIM_STALE_SECONDS:
+                debris.unlink()
+        except OSError:
+            continue
+
+
 def _claim_parked(directory: Path) -> Path | None:
     """Take the oldest abandoned claim, if any lease has actually expired.
 
@@ -364,7 +388,11 @@ def _claim_parked(directory: Path) -> Path | None:
             age = now - orphan.stat().st_mtime
         except OSError:
             continue
-        if age > CLAIM_EXPIRY_SECONDS and _claim_attempt(orphan) >= MAX_CLAIM_ATTEMPTS:
+        # Attempts, not age. Every re-claim touches the mtime and every release
+        # backdates it by a fixed amount, so age is pinned near the stale
+        # threshold and never reaches the expiry. Age stays only as a backstop
+        # for files that never carried an attempt marker.
+        if _claim_attempt(orphan) >= MAX_CLAIM_ATTEMPTS or age > CLAIM_EXPIRY_SECONDS:
             try:
                 orphan.unlink()
             except OSError:
@@ -406,10 +434,14 @@ def _rewrite_claim(claim: Path, remaining: list[dict[str, Any]]) -> bool:
         return True
     temporary = claim.with_suffix(f".{os.getpid()}.partial")
     try:
-        temporary.write_text(
-            "".join(json.dumps(event, separators=(",", ":"), default=str) + "\n" for event in remaining),
-            encoding="utf-8",
-        )
+        payload = "".join(json.dumps(event, separators=(",", ":"), default=str) + "\n" for event in remaining)
+        # fsync before the rename: without it the rename can land while the
+        # bytes have not, and the claim comes back empty or truncated after a
+        # crash. _drain then reads zero events and unlinks it.
+        with open(temporary, "w", encoding="utf-8") as handle:
+            handle.write(payload)
+            handle.flush()
+            os.fsync(handle.fileno())
         temporary.replace(claim)
         _touch(claim)
         return True
@@ -498,6 +530,7 @@ def flush() -> int:
     # Parked batches used to starve behind the live spool indefinitely. Bounded
     # per run so a long backlog cannot turn one flush into an unbounded loop.
     directory = memory_core.data_dir()
+    _sweep_debris(directory)
     for _ in range(MAX_PARKED_PER_RUN):
         parked = _claim_parked(directory)
         if parked is None:
@@ -518,7 +551,18 @@ def _drain(claim: Path | None) -> tuple[int, bool]:
         return 0, True
     try:
         lines = claim.read_text(encoding="utf-8").splitlines()
-    except OSError:
+    except (OSError, ValueError):
+        # ValueError covers UnicodeDecodeError from a torn write. Quarantine
+        # rather than retry: flush() runs from a bare `finally:` in
+        # flush_worker, so raising here also skips the handoff cleanup, and an
+        # undecodable file would otherwise be re-read on every flush forever.
+        try:
+            claim.replace(claim.with_suffix(".corrupt"))
+        except OSError:
+            try:
+                claim.unlink()
+            except OSError:
+                pass
         return 0, True
     events = []
     for line in lines:
@@ -529,8 +573,15 @@ def _drain(claim: Path | None) -> tuple[int, bool]:
         if isinstance(value, dict) and value.get("event"):
             events.append(value)
     if not events:
+        # Only delete when the file really is empty. A non-empty file that
+        # parses to nothing is a torn write, and its contents are the unsent
+        # remainder — deleting it is the data loss this PR exists to prevent.
         try:
-            claim.unlink()
+            empty = claim.stat().st_size == 0
+        except OSError:
+            empty = True
+        try:
+            claim.replace(claim.with_suffix(".corrupt")) if not empty else claim.unlink()
         except OSError:
             pass
         return 0, True
@@ -580,8 +631,13 @@ def _drain(claim: Path | None) -> tuple[int, bool]:
             return sent, False
         sent += len(chunk)
         # Record progress and refresh the lease after each successful batch, so
-        # a crash repeats at most one batch instead of the entire file.
-        _rewrite_claim(claim, events[start + len(chunk) :])
+        # a crash repeats at most one batch instead of the entire file. If the
+        # rewrite fails the claim still holds delivered events, so stop rather
+        # than carry on as though progress were recorded — continuing is how the
+        # duplicate delivery this PR fixes would come back.
+        if not _rewrite_claim(claim, events[start + len(chunk) :]):
+            _release_claim(claim, events[start + len(chunk) :])
+            return sent, False
     return sent, True
 
 
diff --git a/integrations/agent-plugin-core/tests/test_spool_delivery.py b/integrations/agent-plugin-core/tests/test_spool_delivery.py
index 754307454..08266cc98 100644
--- a/integrations/agent-plugin-core/tests/test_spool_delivery.py
+++ b/integrations/agent-plugin-core/tests/test_spool_delivery.py
@@ -112,16 +112,19 @@ def test_a_parked_batch_is_drained_behind_the_live_spool(telemetry):
     assert names == {"code.parked", "code.fresh"}
 
 
-def test_an_untried_batch_is_not_expired_by_age_alone(telemetry):
-    """Expiry should discard what failed, not what never got a turn."""
+def test_a_batch_is_retried_until_the_budget_is_spent_not_discarded(telemetry):
+    """Expiry discards what failed repeatedly, not what merely sat for a while.
+
+    The budget is the attempt count, because age cannot be one: every re-claim
+    touches the mtime and every release backdates it, so age never accumulates.
+    """
     telemetry.record("parked")
     telemetry._post = lambda payload, url: False
     telemetry.flush()
 
     parked = list(telemetry.memory_core.data_dir().glob("telemetry-*.sending"))
     assert len(parked) == 1
-    ancient = time.time() - (telemetry.CLAIM_EXPIRY_SECONDS + 60)
-    os.utime(parked[0], (ancient, ancient))
+    assert telemetry._claim_attempt(parked[0]) < telemetry.MAX_CLAIM_ATTEMPTS
 
     sent: list[dict] = []
     telemetry._post = lambda payload, url: sent.append(payload) or True
@@ -154,11 +157,88 @@ def test_progress_is_recorded_after_every_batch(telemetry):
     assert json.loads(remaining[0])["properties"]["index"] == 200
 
 
-def test_the_heartbeat_stays_well_inside_the_lease(telemetry):
+def test_the_heartbeat_actually_refreshes_the_lease(telemetry):
     """The claim rewrite doubles as the lease heartbeat.
 
-    _post makes a single attempt with SEND_TIMEOUT and no retry, so a heartbeat
-    lands at least that often. If a retry loop is ever added to _post, this is
-    the assertion that catches a sender losing its claim mid-flight.
+    Previously asserted `SEND_TIMEOUT * 4 < CLAIM_STALE_SECONDS`, which compares
+    two constants and executes none of the code under test. Drive the real
+    rewrite and watch the mtime move instead.
     """
-    assert telemetry.SEND_TIMEOUT * 4 < telemetry.CLAIM_STALE_SECONDS
+    for index in range(150):
+        telemetry.record("search", index=index)
+    claim = telemetry._claim_spool()
+    assert claim is not None
+
+    stale = time.time() - (telemetry.CLAIM_STALE_SECONDS + 60)
+    os.utime(claim, (stale, stale))
+    assert time.time() - claim.stat().st_mtime > telemetry.CLAIM_STALE_SECONDS
+
+    telemetry._rewrite_claim(claim, [{"event": "code.x", "properties": {}}])
+    assert time.time() - claim.stat().st_mtime < telemetry.CLAIM_STALE_SECONDS
+
+
+def test_an_undeliverable_batch_is_eventually_given_up_on(telemetry):
+    """Expiry has to be reachable from a state the state machine can produce.
+
+    It was not: every re-claim touched the mtime and every release backdated it
+    by a fixed amount, so age hovered near the stale threshold and the 7-day
+    expiry never fired. An undeliverable batch lived on disk forever, and
+    spawn_flush saw it and started a sender on every hook.
+    """
+    telemetry.record("doomed")
+    telemetry._post = lambda payload, url: False
+
+    for _ in range(telemetry.MAX_CLAIM_ATTEMPTS + 3):
+        telemetry.flush()
+
+    leftover = list(telemetry.memory_core.data_dir().glob("telemetry-*.sending"))
+    assert leftover == [], f"batch never given up on: {[p.name for p in leftover]}"
+
+
+def test_a_legacy_claim_filename_is_not_mistaken_for_a_huge_attempt_count(telemetry):
+    """The old shape is telemetry-<pid>-<hex>.sending, and hex can start with 'a'."""
+    assert telemetry._claim_attempt(Path("telemetry-999-deadbeef.sending")) == 0
+    assert telemetry._claim_attempt(Path("telemetry-999-a1234567.sending")) == 0
+    assert telemetry._claim_attempt(Path("telemetry-999-deadbeef-a2.sending")) == 2
+
+
+def test_a_torn_claim_is_quarantined_not_deleted(telemetry):
+    """A non-empty file that parses to nothing is the remainder, not garbage."""
+    telemetry.record("search")
+    claim = telemetry._claim_spool()
+    claim.write_bytes(b"\xff\xfe not utf-8 at all")
+    stale = time.time() - (telemetry.CLAIM_STALE_SECONDS + 60)
+    os.utime(claim, (stale, stale))
+
+    sent = telemetry.flush()
+
+    assert sent == 0
+    assert not claim.exists()
+    quarantined = list(telemetry.memory_core.data_dir().glob("*.corrupt"))
+    assert len(quarantined) == 1, "torn claim was destroyed instead of kept"
+
+
+def test_a_failed_rewrite_stops_instead_of_redelivering(telemetry):
+    """Ignoring the rewrite result reintroduced the duplicates this PR fixes."""
+    for index in range(250):
+        telemetry.record("search", index=index)
+
+    telemetry._rewrite_claim = lambda claim, remaining: False
+    delivered = []
+    telemetry._post = lambda payload, url: delivered.extend(payload.get("batch", [])) or True
+
+    telemetry.flush()
+    assert len(delivered) == 100, f"kept going after a failed rewrite: {len(delivered)}"
+
+
+def test_partial_files_are_swept(telemetry):
+    """Nothing else globs *.partial, so a crash mid-rename orphans one forever."""
+    data_dir = telemetry.memory_core.data_dir()
+    data_dir.mkdir(parents=True, exist_ok=True)
+    debris = data_dir / "telemetry-1-abc-a0.1.partial"
+    debris.write_text("x", encoding="utf-8")
+    old = time.time() - (telemetry.CLAIM_STALE_SECONDS + 60)
+    os.utime(debris, (old, old))
+
+    telemetry.flush()
+    assert not debris.exists()
diff --git a/integrations/antigravity-plugin/core/telemetry.py b/integrations/antigravity-plugin/core/telemetry.py
index 55ee7c907..fa26cc9a6 100644
--- a/integrations/antigravity-plugin/core/telemetry.py
+++ b/integrations/antigravity-plugin/core/telemetry.py
@@ -313,9 +313,18 @@ def _claim_name(attempt: int = 0) -> str:
 
 
 def _claim_attempt(claim: Path) -> int:
-    """Attempts recorded in a claim filename; 0 for the pre-attempt-count shape."""
+    """Attempts recorded in a claim filename; 0 for the pre-attempt-count shape.
+
+    Anchored on field position, not on a leading "a": the legacy shape is
+    ``telemetry-<pid>-<hex>.sending`` and a hex id such as ``a1234567`` would
+    otherwise parse as attempt 1234567 and be discarded unsent on the first
+    flush after an upgrade.
+    """
     stem = claim.name[: -len(".sending")] if claim.name.endswith(".sending") else claim.name
-    tail = stem.rsplit("-", 1)[-1]
+    parts = stem.split("-")
+    if len(parts) != 4:
+        return 0
+    tail = parts[3]
     if tail.startswith("a") and tail[1:].isdigit():
         return int(tail[1:])
     return 0
@@ -349,6 +358,21 @@ def _claim_spool() -> Path | None:
     return _claim_parked(directory)
 
 
+def _sweep_debris(directory: Path) -> None:
+    """Remove temp files orphaned by a crash between write and rename.
+
+    Neither glob in this module matches *.partial, so nothing else would ever
+    clean them up.
+    """
+    now = time.time()
+    for debris in directory.glob("telemetry-*.partial"):
+        try:
+            if now - debris.stat().st_mtime > CLAIM_STALE_SECONDS:
+                debris.unlink()
+        except OSError:
+            continue
+
+
 def _claim_parked(directory: Path) -> Path | None:
     """Take the oldest abandoned claim, if any lease has actually expired.
 
@@ -364,7 +388,11 @@ def _claim_parked(directory: Path) -> Path | None:
             age = now - orphan.stat().st_mtime
         except OSError:
             continue
-        if age > CLAIM_EXPIRY_SECONDS and _claim_attempt(orphan) >= MAX_CLAIM_ATTEMPTS:
+        # Attempts, not age. Every re-claim touches the mtime and every release
+        # backdates it by a fixed amount, so age is pinned near the stale
+        # threshold and never reaches the expiry. Age stays only as a backstop
+        # for files that never carried an attempt marker.
+        if _claim_attempt(orphan) >= MAX_CLAIM_ATTEMPTS or age > CLAIM_EXPIRY_SECONDS:
             try:
                 orphan.unlink()
             except OSError:
@@ -406,10 +434,14 @@ def _rewrite_claim(claim: Path, remaining: list[dict[str, Any]]) -> bool:
         return True
     temporary = claim.with_suffix(f".{os.getpid()}.partial")
     try:
-        temporary.write_text(
-            "".join(json.dumps(event, separators=(",", ":"), default=str) + "\n" for event in remaining),
-            encoding="utf-8",
-        )
+        payload = "".join(json.dumps(event, separators=(",", ":"), default=str) + "\n" for event in remaining)
+        # fsync before the rename: without it the rename can land while the
+        # bytes have not, and the claim comes back empty or truncated after a
+        # crash. _drain then reads zero events and unlinks it.
+        with open(temporary, "w", encoding="utf-8") as handle:
+            handle.write(payload)
+            handle.flush()
+            os.fsync(handle.fileno())
         temporary.replace(claim)
         _touch(claim)
         return True
@@ -498,6 +530,7 @@ def flush() -> int:
     # Parked batches used to starve behind the live spool indefinitely. Bounded
     # per run so a long backlog cannot turn one flush into an unbounded loop.
     directory = memory_core.data_dir()
+    _sweep_debris(directory)
     for _ in range(MAX_PARKED_PER_RUN):
         parked = _claim_parked(directory)
         if parked is None:
@@ -518,7 +551,18 @@ def _drain(claim: Path | None) -> tuple[int, bool]:
         return 0, True
     try:
         lines = claim.read_text(encoding="utf-8").splitlines()
-    except OSError:
+    except (OSError, ValueError):
+        # ValueError covers UnicodeDecodeError from a torn write. Quarantine
+        # rather than retry: flush() runs from a bare `finally:` in
+        # flush_worker, so raising here also skips the handoff cleanup, and an
+        # undecodable file would otherwise be re-read on every flush forever.
+        try:
+            claim.replace(claim.with_suffix(".corrupt"))
+        except OSError:
+            try:
+                claim.unlink()
+            except OSError:
+                pass
         return 0, True
     events = []
     for line in lines:
@@ -529,8 +573,15 @@ def _drain(claim: Path | None) -> tuple[int, bool]:
         if isinstance(value, dict) and value.get("event"):
             events.append(value)
     if not events:
+        # Only delete when the file really is empty. A non-empty file that
+        # parses to nothing is a torn write, and its contents are the unsent
+        # remainder — deleting it is the data loss this PR exists to prevent.
         try:
-            claim.unlink()
+            empty = claim.stat().st_size == 0
+        except OSError:
+            empty = True
+        try:
+            claim.replace(claim.with_suffix(".corrupt")) if not empty else claim.unlink()
         except OSError:
             pass
         return 0, True
@@ -580,8 +631,13 @@ def _drain(claim: Path | None) -> tuple[int, bool]:
             return sent, False
         sent += len(chunk)
         # Record progress and refresh the lease after each successful batch, so
-        # a crash repeats at most one batch instead of the entire file.
-        _rewrite_claim(claim, events[start + len(chunk) :])
+        # a crash repeats at most one batch instead of the entire file. If the
+        # rewrite fails the claim still holds delivered events, so stop rather
+        # than carry on as though progress were recorded — continuing is how the
+        # duplicate delivery this PR fixes would come back.
+        if not _rewrite_claim(claim, events[start + len(chunk) :]):
+            _release_claim(claim, events[start + len(chunk) :])
+            return sent, False
     return sent, True
 
 
diff --git a/integrations/claude-code-plugin/core/telemetry.py b/integrations/claude-code-plugin/core/telemetry.py
index 55ee7c907..fa26cc9a6 100644
--- a/integrations/claude-code-plugin/core/telemetry.py
+++ b/integrations/claude-code-plugin/core/telemetry.py
@@ -313,9 +313,18 @@ def _claim_name(attempt: int = 0) -> str:
 
 
 def _claim_attempt(claim: Path) -> int:
-    """Attempts recorded in a claim filename; 0 for the pre-attempt-count shape."""
+    """Attempts recorded in a claim filename; 0 for the pre-attempt-count shape.
+
+    Anchored on field position, not on a leading "a": the legacy shape is
+    ``telemetry-<pid>-<hex>.sending`` and a hex id such as ``a1234567`` would
+    otherwise parse as attempt 1234567 and be discarded unsent on the first
+    flush after an upgrade.
+    """
     stem = claim.name[: -len(".sending")] if claim.name.endswith(".sending") else claim.name
-    tail = stem.rsplit("-", 1)[-1]
+    parts = stem.split("-")
+    if len(parts) != 4:
+        return 0
+    tail = parts[3]
     if tail.startswith("a") and tail[1:].isdigit():
         return int(tail[1:])
     return 0
@@ -349,6 +358,21 @@ def _claim_spool() -> Path | None:
     return _claim_parked(directory)
 
 
+def _sweep_debris(directory: Path) -> None:
+    """Remove temp files orphaned by a crash between write and rename.
+
+    Neither glob in this module matches *.partial, so nothing else would ever
+    clean them up.
+    """
+    now = time.time()
+    for debris in directory.glob("telemetry-*.partial"):
+        try:
+            if now - debris.stat().st_mtime > CLAIM_STALE_SECONDS:
+                debris.unlink()
+        except OSError:
+            continue
+
+
 def _claim_parked(directory: Path) -> Path | None:
     """Take the oldest abandoned claim, if any lease has actually expired.
 
@@ -364,7 +388,11 @@ def _claim_parked(directory: Path) -> Path | None:
             age = now - orphan.stat().st_mtime
         except OSError:
             continue
-        if age > CLAIM_EXPIRY_SECONDS and _claim_attempt(orphan) >= MAX_CLAIM_ATTEMPTS:
+        # Attempts, not age. Every re-claim touches the mtime and every release
+        # backdates it by a fixed amount, so age is pinned near the stale
+        # threshold and never reaches the expiry. Age stays only as a backstop
+        # for files that never carried an attempt marker.
+        if _claim_attempt(orphan) >= MAX_CLAIM_ATTEMPTS or age > CLAIM_EXPIRY_SECONDS:
             try:
                 orphan.unlink()
             except OSError:
@@ -406,10 +434,14 @@ def _rewrite_claim(claim: Path, remaining: list[dict[str, Any]]) -> bool:
         return True
     temporary = claim.with_suffix(f".{os.getpid()}.partial")
     try:
-        temporary.write_text(
-            "".join(json.dumps(event, separators=(",", ":"), default=str) + "\n" for event in remaining),
-            encoding="utf-8",
-        )
+        payload = "".join(json.dumps(event, separators=(",", ":"), default=str) + "\n" for event in remaining)
+        # fsync before the rename: without it the rename can land while the
+        # bytes have not, and the claim comes back empty or truncated after a
+        # crash. _drain then reads zero events and unlinks it.
+        with open(temporary, "w", encoding="utf-8") as handle:
+            handle.write(payload)
+            handle.flush()
+            os.fsync(handle.fileno())
         temporary.replace(claim)
         _touch(claim)
         return True
@@ -498,6 +530,7 @@ def flush() -> int:
     # Parked batches used to starve behind the live spool indefinitely. Bounded
     # per run so a long backlog cannot turn one flush into an unbounded loop.
     directory = memory_core.data_dir()
+    _sweep_debris(directory)
     for _ in range(MAX_PARKED_PER_RUN):
         parked = _claim_parked(directory)
         if parked is None:
@@ -518,7 +551,18 @@ def _drain(claim: Path | None) -> tuple[int, bool]:
         return 0, True
     try:
         lines = claim.read_text(encoding="utf-8").splitlines()
-    except OSError:
+    except (OSError, ValueError):
+        # ValueError covers UnicodeDecodeError from a torn write. Quarantine
+        # rather than retry: flush() runs from a bare `finally:` in
+        # flush_worker, so raising here also skips the handoff cleanup, and an
+        # undecodable file would otherwise be re-read on every flush forever.
+        try:
+            claim.replace(claim.with_suffix(".corrupt"))
+        except OSError:
+            try:
+                claim.unlink()
+            except OSError:
+                pass
         return 0, True
     events = []
     for line in lines:
@@ -529,8 +573,15 @@ def _drain(claim: Path | None) -> tuple[int, bool]:
         if isinstance(value, dict) and value.get("event"):
             events.append(value)
     if not events:
+        # Only delete when the file really is empty. A non-empty file that
+        # parses to nothing is a torn write, and its contents are the unsent
+        # remainder — deleting it is the data loss this PR exists to prevent.
         try:
-            claim.unlink()
+            empty = claim.stat().st_size == 0
+        except OSError:
+            empty = True
+        try:
+            claim.replace(claim.with_suffix(".corrupt")) if not empty else claim.unlink()
         except OSError:
             pass
         return 0, True
@@ -580,8 +631,13 @@ def _drain(claim: Path | None) -> tuple[int, bool]:
             return sent, False
         sent += len(chunk)
         # Record progress and refresh the lease after each successful batch, so
-        # a crash repeats at most one batch instead of the entire file.
-        _rewrite_claim(claim, events[start + len(chunk) :])
+        # a crash repeats at most one batch instead of the entire file. If the
+        # rewrite fails the claim still holds delivered events, so stop rather
+        # than carry on as though progress were recorded — continuing is how the
+        # duplicate delivery this PR fixes would come back.
+        if not _rewrite_claim(claim, events[start + len(chunk) :]):
+            _release_claim(claim, events[start + len(chunk) :])
+            return sent, False
     return sent, True
 
 
diff --git a/integrations/codex-plugin/core/telemetry.py b/integrations/codex-plugin/core/telemetry.py
index 55ee7c907..fa26cc9a6 100644
--- a/integrations/codex-plugin/core/telemetry.py
+++ b/integrations/codex-plugin/core/telemetry.py
@@ -313,9 +313,18 @@ def _claim_name(attempt: int = 0) -> str:
 
 
 def _claim_attempt(claim: Path) -> int:
-    """Attempts recorded in a claim filename; 0 for the pre-attempt-count shape."""
+    """Attempts recorded in a claim filename; 0 for the pre-attempt-count shape.
+
+    Anchored on field position, not on a leading "a": the legacy shape is
+    ``telemetry-<pid>-<hex>.sending`` and a hex id such as ``a1234567`` would
+    otherwise parse as attempt 1234567 and be discarded unsent on the first
+    flush after an upgrade.
+    """
     stem = claim.name[: -len(".sending")] if claim.name.endswith(".sending") else claim.name
-    tail = stem.rsplit("-", 1)[-1]
+    parts = stem.split("-")
+    if len(parts) != 4:
+        return 0
+    tail = parts[3]
     if tail.startswith("a") and tail[1:].isdigit():
         return int(tail[1:])
     return 0
@@ -349,6 +358,21 @@ def _claim_spool() -> Path | None:
     return _claim_parked(directory)
 
 
+def _sweep_debris(directory: Path) -> None:
+    """Remove temp files orphaned by a crash between write and rename.
+
+    Neither glob in this module matches *.partial, so nothing else would ever
+    clean them up.
+    """
+    now = time.time()
+    for debris in directory.glob("telemetry-*.partial"):
+        try:
+            if now - debris.stat().st_mtime > CLAIM_STALE_SECONDS:
+                debris.unlink()
+        except OSError:
+            continue
+
+
 def _claim_parked(directory: Path) -> Path | None:
     """Take the oldest abandoned claim, if any lease has actually expired.
 
@@ -364,7 +388,11 @@ def _claim_parked(directory: Path) -> Path | None:
             age = now - orphan.stat().st_mtime
         except OSError:
             continue
-        if age > CLAIM_EXPIRY_SECONDS and _claim_attempt(orphan) >= MAX_CLAIM_ATTEMPTS:
+        # Attempts, not age. Every re-claim touches the mtime and every release
+        # backdates it by a fixed amount, so age is pinned near the stale
+        # threshold and never reaches the expiry. Age stays only as a backstop
+        # for files that never carried an attempt marker.
+        if _claim_attempt(orphan) >= MAX_CLAIM_ATTEMPTS or age > CLAIM_EXPIRY_SECONDS:
             try:
                 orphan.unlink()
             except OSError:
@@ -406,10 +434,14 @@ def _rewrite_claim(claim: Path, remaining: list[dict[str, Any]]) -> bool:
         return True
     temporary = claim.with_suffix(f".{os.getpid()}.partial")
     try:
-        temporary.write_text(
-            "".join(json.dumps(event, separators=(",", ":"), default=str) + "\n" for event in remaining),
-            encoding="utf-8",
-        )
+        payload = "".join(json.dumps(event, separators=(",", ":"), default=str) + "\n" for event in remaining)
+        # fsync before the rename: without it the rename can land while the
+        # bytes have not, and the claim comes back empty or truncated after a
+        # crash. _drain then reads zero events and unlinks it.
+        with open(temporary, "w", encoding="utf-8") as handle:
+            handle.write(payload)
+            handle.flush()
+            os.fsync(handle.fileno())
         temporary.replace(claim)
         _touch(claim)
         return True
@@ -498,6 +530,7 @@ def flush() -> int:
     # Parked batches used to starve behind the live spool indefinitely. Bounded
     # per run so a long backlog cannot turn one flush into an unbounded loop.
     directory = memory_core.data_dir()
+    _sweep_debris(directory)
     for _ in range(MAX_PARKED_PER_RUN):
         parked = _claim_parked(directory)
         if parked is None:
@@ -518,7 +551,18 @@ def _drain(claim: Path | None) -> tuple[int, bool]:
         return 0, True
     try:
         lines = claim.read_text(encoding="utf-8").splitlines()
-    except OSError:
+    except (OSError, ValueError):
+        # ValueError covers UnicodeDecodeError from a torn write. Quarantine
+        # rather than retry: flush() runs from a bare `finally:` in
+        # flush_worker, so raising here also skips the handoff cleanup, and an
+        # undecodable file would otherwise be re-read on every flush forever.
+        try:
+            claim.replace(claim.with_suffix(".corrupt"))
+        except OSError:
+            try:
+                claim.unlink()
+            except OSError:
+                pass
         return 0, True
     events = []
     for line in lines:
@@ -529,8 +573,15 @@ def _drain(claim: Path | None) -> tuple[int, bool]:
         if isinstance(value, dict) and value.get("event"):
             events.append(value)
     if not events:
+        # Only delete when the file really is empty. A non-empty file that
+        # parses to nothing is a torn write, and its contents are the unsent
+        # remainder — deleting it is the data loss this PR exists to prevent.
         try:
-            claim.unlink()
+            empty = claim.stat().st_size == 0
+        except OSError:
+            empty = True
+        try:
+            claim.replace(claim.with_suffix(".corrupt")) if not empty else claim.unlink()
         except OSError:
             pass
         return 0, True
@@ -580,8 +631,13 @@ def _drain(claim: Path | None) -> tuple[int, bool]:
             return sent, False
         sent += len(chunk)
         # Record progress and refresh the lease after each successful batch, so
-        # a crash repeats at most one batch instead of the entire file.
-        _rewrite_claim(claim, events[start + len(chunk) :])
+        # a crash repeats at most one batch instead of the entire file. If the
+        # rewrite fails the claim still holds delivered events, so stop rather
+        # than carry on as though progress were recorded — continuing is how the
+        # duplicate delivery this PR fixes would come back.
+        if not _rewrite_claim(claim, events[start + len(chunk) :]):
+            _release_claim(claim, events[start + len(chunk) :])
+            return sent, False
     return sent, True
 
 
diff --git a/integrations/cursor-plugin/core/telemetry.py b/integrations/cursor-plugin/core/telemetry.py
index 55ee7c907..fa26cc9a6 100644
--- a/integrations/cursor-plugin/core/telemetry.py
+++ b/integrations/cursor-plugin/core/telemetry.py
@@ -313,9 +313,18 @@ def _claim_name(attempt: int = 0) -> str:
 
 
 def _claim_attempt(claim: Path) -> int:
-    """Attempts recorded in a claim filename; 0 for the pre-attempt-count shape."""
+    """Attempts recorded in a claim filename; 0 for the pre-attempt-count shape.
+
+    Anchored on field position, not on a leading "a": the legacy shape is
+    ``telemetry-<pid>-<hex>.sending`` and a hex id such as ``a1234567`` would
+    otherwise parse as attempt 1234567 and be discarded unsent on the first
+    flush after an upgrade.
+    """
     stem = claim.name[: -len(".sending")] if claim.name.endswith(".sending") else claim.name
-    tail = stem.rsplit("-", 1)[-1]
+    parts = stem.split("-")
+    if len(parts) != 4:
+        return 0
+    tail = parts[3]
     if tail.startswith("a") and tail[1:].isdigit():
         return int(tail[1:])
     return 0
@@ -349,6 +358,21 @@ def _claim_spool() -> Path | None:
     return _claim_parked(directory)
 
 
+def _sweep_debris(directory: Path) -> None:
+    """Remove temp files orphaned by a crash between write and rename.
+
+    Neither glob in this module matches *.partial, so nothing else would ever
+    clean them up.
+    """
+    now = time.time()
+    for debris in directory.glob("telemetry-*.partial"):
+        try:
+            if now - debris.stat().st_mtime > CLAIM_STALE_SECONDS:
+                debris.unlink()
+        except OSError:
+            continue
+
+
 def _claim_parked(directory: Path) -> Path | None:
     """Take the oldest abandoned claim, if any lease has actually expired.
 
@@ -364,7 +388,11 @@ def _claim_parked(directory: Path) -> Path | None:
             age = now - orphan.stat().st_mtime
         except OSError:
             continue
-        if age > CLAIM_EXPIRY_SECONDS and _claim_attempt(orphan) >= MAX_CLAIM_ATTEMPTS:
+        # Attempts, not age. Every re-claim touches the mtime and every release
+        # backdates it by a fixed amount, so age is pinned near the stale
+        # threshold and never reaches the expiry. Age stays only as a backstop
+        # for files that never carried an attempt marker.
+        if _claim_attempt(orphan) >= MAX_CLAIM_ATTEMPTS or age > CLAIM_EXPIRY_SECONDS:
             try:
                 orphan.unlink()
             except OSError:
@@ -406,10 +434,14 @@ def _rewrite_claim(claim: Path, remaining: list[dict[str, Any]]) -> bool:
         return True
     temporary = claim.with_suffix(f".{os.getpid()}.partial")
     try:
-        temporary.write_text(
-            "".join(json.dumps(event, separators=(",", ":"), default=str) + "\n" for event in remaining),
-            encoding="utf-8",
-        )
+        payload = "".join(json.dumps(event, separators=(",", ":"), default=str) + "\n" for event in remaining)
+        # fsync before the rename: without it the rename can land while the
+        # bytes have not, and the claim comes back empty or truncated after a
+        # crash. _drain then reads zero events and unlinks it.
+        with open(temporary, "w", encoding="utf-8") as handle:
+            handle.write(payload)
+            handle.flush()
+            os.fsync(handle.fileno())
         temporary.replace(claim)
         _touch(claim)
         return True
@@ -498,6 +530,7 @@ def flush() -> int:
     # Parked batches used to starve behind the live spool indefinitely. Bounded
     # per run so a long backlog cannot turn one flush into an unbounded loop.
     directory = memory_core.data_dir()
+    _sweep_debris(directory)
     for _ in range(MAX_PARKED_PER_RUN):
         parked = _claim_parked(directory)
         if parked is None:
@@ -518,7 +551,18 @@ def _drain(claim: Path | None) -> tuple[int, bool]:
         return 0, True
     try:
         lines = claim.read_text(encoding="utf-8").splitlines()
-    except OSError:
+    except (OSError, ValueError):
+        # ValueError covers UnicodeDecodeError from a torn write. Quarantine
+        # rather than retry: flush() runs from a bare `finally:` in
+        # flush_worker, so raising here also skips the handoff cleanup, and an
+        # undecodable file would otherwise be re-read on every flush forever.
+        try:
+            claim.replace(claim.with_suffix(".corrupt"))
+        except OSError:
+            try:
+                claim.unlink()
+            except OSError:
+                pass
         return 0, True
     events = []
     for line in lines:
@@ -529,8 +573,15 @@ def _drain(claim: Path | None) -> tuple[int, bool]:
         if isinstance(value, dict) and value.get("event"):
             events.append(value)
     if not events:
+        # Only delete when the file really is empty. A non-empty file that
+        # parses to nothing is a torn write, and its contents are the unsent
+        # remainder — deleting it is the data loss this PR exists to prevent.
         try:
-            claim.unlink()
+            empty = claim.stat().st_size == 0
+        except OSError:
+            empty = True
+        try:
+            claim.replace(claim.with_suffix(".corrupt")) if not empty else claim.unlink()
         except OSError:
             pass
         return 0, True
@@ -580,8 +631,13 @@ def _drain(claim: Path | None) -> tuple[int, bool]:
             return sent, False
         sent += len(chunk)
         # Record progress and refresh the lease after each successful batch, so
-        # a crash repeats at most one batch instead of the entire file.
-        _rewrite_claim(claim, events[start + len(chunk) :])
+        # a crash repeats at most one batch instead of the entire file. If the
+        # rewrite fails the claim still holds delivered events, so stop rather
+        # than carry on as though progress were recorded — continuing is how the
+        # duplicate delivery this PR fixes would come back.
+        if not _rewrite_claim(claim, events[start + len(chunk) :]):
+            _release_claim(claim, events[start + len(chunk) :])
+            return sent, False
     return sent, True
 
 
diff --git a/integrations/kimi-plugin/core/telemetry.py b/integrations/kimi-plugin/core/telemetry.py
index 55ee7c907..fa26cc9a6 100644
--- a/integrations/kimi-plugin/core/telemetry.py
+++ b/integrations/kimi-plugin/core/telemetry.py
@@ -313,9 +313,18 @@ def _claim_name(attempt: int = 0) -> str:
 
 
 def _claim_attempt(claim: Path) -> int:
-    """Attempts recorded in a claim filename; 0 for the pre-attempt-count shape."""
+    """Attempts recorded in a claim filename; 0 for the pre-attempt-count shape.
+
+    Anchored on field position, not on a leading "a": the legacy shape is
+    ``telemetry-<pid>-<hex>.sending`` and a hex id such as ``a1234567`` would
+    otherwise parse as attempt 1234567 and be discarded unsent on the first
+    flush after an upgrade.
+    """
     stem = claim.name[: -len(".sending")] if claim.name.endswith(".sending") else claim.name
-    tail = stem.rsplit("-", 1)[-1]
+    parts = stem.split("-")
+    if len(parts) != 4:
+        return 0
+    tail = parts[3]
     if tail.startswith("a") and tail[1:].isdigit():
         return int(tail[1:])
     return 0
@@ -349,6 +358,21 @@ def _claim_spool() -> Path | None:
     return _claim_parked(directory)
 
 
+def _sweep_debris(directory: Path) -> None:
+    """Remove temp files orphaned by a crash between write and rename.
+
+    Neither glob in this module matches *.partial, so nothing else would ever
+    clean them up.
+    """
+    now = time.time()
+    for debris in directory.glob("telemetry-*.partial"):
+        try:
+            if now - debris.stat().st_mtime > CLAIM_STALE_SECONDS:
+                debris.unlink()
+        except OSError:
+            continue
+
+
 def _claim_parked(directory: Path) -> Path | None:
     """Take the oldest abandoned claim, if any lease has actually expired.
 
@@ -364,7 +388,11 @@ def _claim_parked(directory: Path) -> Path | None:
             age = now - orphan.stat().st_mtime
         except OSError:
             continue
-        if age > CLAIM_EXPIRY_SECONDS and _claim_attempt(orphan) >= MAX_CLAIM_ATTEMPTS:
+        # Attempts, not age. Every re-claim touches the mtime and every release
+        # backdates it by a fixed amount, so age is pinned near the stale
+        # threshold and never reaches the expiry. Age stays only as a backstop
+        # for files that never carried an attempt marker.
+        if _claim_attempt(orphan) >= MAX_CLAIM_ATTEMPTS or age > CLAIM_EXPIRY_SECONDS:
             try:
                 orphan.unlink()
             except OSError:
@@ -406,10 +434,14 @@ def _rewrite_claim(claim: Path, remaining: list[dict[str, Any]]) -> bool:
         return True
     temporary = claim.with_suffix(f".{os.getpid()}.partial")
     try:
-        temporary.write_text(
-            "".join(json.dumps(event, separators=(",", ":"), default=str) + "\n" for event in remaining),
-            encoding="utf-8",
-        )
+        payload = "".join(json.dumps(event, separators=(",", ":"), default=str) + "\n" for event in remaining)
+        # fsync before the rename: without it the rename can land while the
+        # bytes have not, and the claim comes back empty or truncated after a
+        # crash. _drain then reads zero events and unlinks it.
+        with open(temporary, "w", encoding="utf-8") as handle:
+            handle.write(payload)
+            handle.flush()
+            os.fsync(handle.fileno())
         temporary.replace(claim)
         _touch(claim)
         return True
@@ -498,6 +530,7 @@ def flush() -> int:
     # Parked batches used to starve behind the live spool indefinitely. Bounded
     # per run so a long backlog cannot turn one flush into an unbounded loop.
     directory = memory_core.data_dir()
+    _sweep_debris(directory)
     for _ in range(MAX_PARKED_PER_RUN):
         parked = _claim_parked(directory)
         if parked is None:
@@ -518,7 +551,18 @@ def _drain(claim: Path | None) -> tuple[int, bool]:
         return 0, True
     try:
         lines = claim.read_text(encoding="utf-8").splitlines()
-    except OSError:
+    except (OSError, ValueError):
+        # ValueError covers UnicodeDecodeError from a torn write. Quarantine
+        # rather than retry: flush() runs from a bare `finally:` in
+        # flush_worker, so raising here also skips the handoff cleanup, and an
+        # undecodable file would otherwise be re-read on every flush forever.
+        try:
+            claim.replace(claim.with_suffix(".corrupt"))
+        except OSError:
+            try:
+                claim.unlink()
+            except OSError:
+                pass
         return 0, True
     events = []
     for line in lines:
@@ -529,8 +573,15 @@ def _drain(claim: Path | None) -> tuple[int, bool]:
         if isinstance(value, dict) and value.get("event"):
             events.append(value)
     if not events:
+        # Only delete when the file really is empty. A non-empty file that
+        # parses to nothing is a torn write, and its contents are the unsent
+        # remainder — deleting it is the data loss this PR exists to prevent.
         try:
-            claim.unlink()
+            empty = claim.stat().st_size == 0
+        except OSError:
+            empty = True
+        try:
+            claim.replace(claim.with_suffix(".corrupt")) if not empty else claim.unlink()
         except OSError:
             pass
         return 0, True
@@ -580,8 +631,13 @@ def _drain(claim: Path | None) -> tuple[int, bool]:
             return sent, False
         sent += len(chunk)
         # Record progress and refresh the lease after each successful batch, so
-        # a crash repeats at most one batch instead of the entire file.
-        _rewrite_claim(claim, events[start + len(chunk) :])
+        # a crash repeats at most one batch instead of the entire file. If the
+        # rewrite fails the claim still holds delivered events, so stop rather
+        # than carry on as though progress were recorded — continuing is how the
+        # duplicate delivery this PR fixes would come back.
+        if not _rewrite_claim(claim, events[start + len(chunk) :]):
+            _release_claim(claim, events[start + len(chunk) :])
+            return sent, False
     return sent, True
 
 
diff --git a/integrations/mem0-agent-plugin/core/telemetry.py b/integrations/mem0-agent-plugin/core/telemetry.py
index 55ee7c907..fa26cc9a6 100644
--- a/integrations/mem0-agent-plugin/core/telemetry.py
+++ b/integrations/mem0-agent-plugin/core/telemetry.py
@@ -313,9 +313,18 @@ def _claim_name(attempt: int = 0) -> str:
 
 
 def _claim_attempt(claim: Path) -> int:
-    """Attempts recorded in a claim filename; 0 for the pre-attempt-count shape."""
+    """Attempts recorded in a claim filename; 0 for the pre-attempt-count shape.
+
+    Anchored on field position, not on a leading "a": the legacy shape is
+    ``telemetry-<pid>-<hex>.sending`` and a hex id such as ``a1234567`` would
+    otherwise parse as attempt 1234567 and be discarded unsent on the first
+    flush after an upgrade.
+    """
     stem = claim.name[: -len(".sending")] if claim.name.endswith(".sending") else claim.name
-    tail = stem.rsplit("-", 1)[-1]
+    parts = stem.split("-")
+    if len(parts) != 4:
+        return 0
+    tail = parts[3]
     if tail.startswith("a") and tail[1:].isdigit():
         return int(tail[1:])
     return 0
@@ -349,6 +358,21 @@ def _claim_spool() -> Path | None:
     return _claim_parked(directory)
 
 
+def _sweep_debris(directory: Path) -> None:
+    """Remove temp files orphaned by a crash between write and rename.
+
+    Neither glob in this module matches *.partial, so nothing else would ever
+    clean them up.
+    """
+    now = time.time()
+    for debris in directory.glob("telemetry-*.partial"):
+        try:
+            if now - debris.stat().st_mtime > CLAIM_STALE_SECONDS:
+                debris.unlink()
+        except OSError:
+            continue
+
+
 def _claim_parked(directory: Path) -> Path | None:
     """Take the oldest abandoned claim, if any lease has actually expired.
 
@@ -364,7 +388,11 @@ def _claim_parked(directory: Path) -> Path | None:
             age = now - orphan.stat().st_mtime
         except OSError:
             continue
-        if age > CLAIM_EXPIRY_SECONDS and _claim_attempt(orphan) >= MAX_CLAIM_ATTEMPTS:
+        # Attempts, not age. Every re-claim touches the mtime and every release
+        # backdates it by a fixed amount, so age is pinned near the stale
+        # threshold and never reaches the expiry. Age stays only as a backstop
+        # for files that never carried an attempt marker.
+        if _claim_attempt(orphan) >= MAX_CLAIM_ATTEMPTS or age > CLAIM_EXPIRY_SECONDS:
             try:
                 orphan.unlink()
             except OSError:
@@ -406,10 +434,14 @@ def _rewrite_claim(claim: Path, remaining: list[dict[str, Any]]) -> bool:
         return True
     temporary = claim.with_suffix(f".{os.getpid()}.partial")
     try:
-        temporary.write_text(
-            "".join(json.dumps(event, separators=(",", ":"), default=str) + "\n" for event in remaining),
-            encoding="utf-8",
-        )
+        payload = "".join(json.dumps(event, separators=(",", ":"), default=str) + "\n" for event in remaining)
+        # fsync before the rename: without it the rename can land while the
+        # bytes have not, and the claim comes back empty or truncated after a
+        # crash. _drain then reads zero events and unlinks it.
+        with open(temporary, "w", encoding="utf-8") as handle:
+            handle.write(payload)
+            handle.flush()
+            os.fsync(handle.fileno())
         temporary.replace(claim)
         _touch(claim)
         return True
@@ -498,6 +530,7 @@ def flush() -> int:
     # Parked batches used to starve behind the live spool indefinitely. Bounded
     # per run so a long backlog cannot turn one flush into an unbounded loop.
     directory = memory_core.data_dir()
+    _sweep_debris(directory)
     for _ in range(MAX_PARKED_PER_RUN):
         parked = _claim_parked(directory)
         if parked is None:
@@ -518,7 +551,18 @@ def _drain(claim: Path | None) -> tuple[int, bool]:
         return 0, True
     try:
         lines = claim.read_text(encoding="utf-8").splitlines()
-    except OSError:
+    except (OSError, ValueError):
+        # ValueError covers UnicodeDecodeError from a torn write. Quarantine
+        # rather than retry: flush() runs from a bare `finally:` in
+        # flush_worker, so raising here also skips the handoff cleanup, and an
+        # undecodable file would otherwise be re-read on every flush forever.
+        try:
+            claim.replace(claim.with_suffix(".corrupt"))
+        except OSError:
+            try:
+                claim.unlink()
+            except OSError:
+                pass
         return 0, True
     events = []
     for line in lines:
@@ -529,8 +573,15 @@ def _drain(claim: Path | None) -> tuple[int, bool]:
         if isinstance(value, dict) and value.get("event"):
             events.append(value)
     if not events:
+        # Only delete when the file really is empty. A non-empty file that
+        # parses to nothing is a torn write, and its contents are the unsent
+        # remainder — deleting it is the data loss this PR exists to prevent.
         try:
-            claim.unlink()
+            empty = claim.stat().st_size == 0
+        except OSError:
+            empty = True
+        try:
+            claim.replace(claim.with_suffix(".corrupt")) if not empty else claim.unlink()
         except OSError:
             pass
         return 0, True
@@ -580,8 +631,13 @@ def _drain(claim: Path | None) -> tuple[int, bool]:
             return sent, False
         sent += len(chunk)
         # Record progress and refresh the lease after each successful batch, so
-        # a crash repeats at most one batch instead of the entire file.
-        _rewrite_claim(claim, events[start + len(chunk) :])
+        # a crash repeats at most one batch instead of the entire file. If the
+        # rewrite fails the claim still holds delivered events, so stop rather
+        # than carry on as though progress were recorded — continuing is how the
+        # duplicate delivery this PR fixes would come back.
+        if not _rewrite_claim(claim, events[start + len(chunk) :]):
+            _release_claim(claim, events[start + len(chunk) :])
+            return sent, False
     return sent, True