Rename checkpoint trigger file to be product-agnostic (#704)

* Rename checkpoint trigger file to be product-agnostic

The on-demand checkpoint sentinel file in /dev/shm was named
"instructlab_checkpoint_requested" — rename it to the generic
"checkpoint_requested" so the mechanism is not tied to a specific
product name.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* Allow checkpoint trigger filename to be overridden via env var

Read CHECKPOINT_TRIGGER_FILENAME from os.environ at call time in
_get_trigger_path() instead of using a module-level constant. This
lets users customize the trigger filename for environments where
multiple training jobs share the same /dev/shm.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: RobotSail

docs/on_demand_checkpointing.md

@@ -135,9 +135,13 @@ The trigger file is always at a fixed path. To trigger a checkpoint
 (e.g. via `kubectl exec` into the training pod):
 
 ```bash
-touch /dev/shm/instructlab_checkpoint_requested
+touch /dev/shm/checkpoint_requested
 ```
 
+The default filename is `checkpoint_requested`. To use a custom filename,
+set the `CHECKPOINT_TRIGGER_FILENAME` environment variable before starting
+training.
+
 Workers check for the trigger file at each synchronization point in the
 training loop (multiple times per step). Once any rank on any node detects
 it, all ranks coordinate via `all_reduce` to save a checkpoint and exit.

src/instructlab/training/on_demand_checkpoint.py

@@ -89,12 +89,12 @@
 #   2. Shared between all containers in the same Kubernetes pod.
 #   3. Automatically cleaned up when the pod is destroyed.
 _TRIGGER_DIR = Path("/dev/shm")
-_TRIGGER_FILENAME = "instructlab_checkpoint_requested"
 
 
 def _get_trigger_path() -> Path:
     """Return the path to the checkpoint trigger file."""
-    return _TRIGGER_DIR / _TRIGGER_FILENAME
+    filename = os.environ.get("CHECKPOINT_TRIGGER_FILENAME", "checkpoint_requested")
+    return _TRIGGER_DIR / filename
 
 
 def write_trigger_file() -> Path:

tests/unit/test_on_demand_checkpoint.py

@@ -29,7 +29,13 @@
 class TestGetTriggerPath:
     def test_returns_correct_name(self):
         path = _get_trigger_path()
-        assert path.name == "instructlab_checkpoint_requested"
+        assert path.name == "checkpoint_requested"
+        assert str(path.parent) == "/dev/shm"
+
+    def test_respects_env_override(self, monkeypatch):
+        monkeypatch.setenv("CHECKPOINT_TRIGGER_FILENAME", "my_custom_trigger")
+        path = _get_trigger_path()
+        assert path.name == "my_custom_trigger"
         assert str(path.parent) == "/dev/shm"
 
 
@@ -43,7 +49,7 @@ def test_creates_file(self, tmp_path):
     def test_returns_correct_path(self, tmp_path):
         with patch("instructlab.training.on_demand_checkpoint._TRIGGER_DIR", tmp_path):
             path = write_trigger_file()
-            assert path == tmp_path / "instructlab_checkpoint_requested"
+            assert path == tmp_path / "checkpoint_requested"
 
 
 class TestTriggerFileExists: