diff --git a/services/lora-training-worker/tests/test_invocation.py b/services/lora-training-worker/tests/test_invocation.py
index 29f9d7a..73a2b98 100644
--- a/services/lora-training-worker/tests/test_invocation.py
+++ b/services/lora-training-worker/tests/test_invocation.py
@@ -107,6 +107,21 @@ def test_published_relative_path():
     ) == "trained/392cf898ac03/sindra_lora.safetensors"
 
 
+def test_published_relative_path_explicit_train_id_wins():
+    # explicit train_id (arbo now sends it) takes precedence over the path-derived fallback
+    assert published_relative_path(
+        "/worktank/arbo/train/whatever/output", "sindra_lora", train_id="abc123"
+    ) == "trained/abc123/sindra_lora.safetensors"
+
+
+def test_train_id_optional_and_validated():
+    # absent -> OK (falls back to derivation); present+safe -> OK; present+unsafe -> 422
+    build_command(_req())  # no train_id key
+    build_command(_req(train_id="392cf898ac03"))
+    with pytest.raises(InvalidTrainRequest, match="train_id"):
+        build_command(_req(train_id="../../etc"))
+
+
 def test_storetank_checkpoint_allowed():
     # the canonical SDXL store (2026-06-13 move) — arbo dispatches base_model_path from here
     argv, _, _ = build_command(
diff --git a/services/lora-training-worker/worker/app.py b/services/lora-training-worker/worker/app.py
index fc91438..7d0a1a1 100644
--- a/services/lora-training-worker/worker/app.py
+++ b/services/lora-training-worker/worker/app.py
@@ -39,6 +39,7 @@ class TrainRequest(BaseModel):
     tier: str
     device_index: int = Field(ge=0, le=1)
     seed: int = Field(default=42, ge=0)
+    train_id: str | None = None  # Phase 2: arbo's id, the publish-path namespace (optional)
 
 
 @app.post("/train")
diff --git a/services/lora-training-worker/worker/invocation.py b/services/lora-training-worker/worker/invocation.py
index b818c50..9e0ee59 100644
--- a/services/lora-training-worker/worker/invocation.py
+++ b/services/lora-training-worker/worker/invocation.py
@@ -84,6 +84,14 @@ def validate_request(req: dict) -> dict:
     seed = req.get("seed", 42)
     _require(isinstance(seed, int) and 0 <= seed <= 2**31 - 1, "seed must be a non-negative int32")
 
+    # ---- train_id (optional; arbo's id — the publish-path namespace, Phase 2) -------
+    # Explicit over the derive-from-output_dir.parent fallback (decouples the worker from
+    # arbo's handoff layout). Path-safe token since it lands in the loras/trained/{train_id}/ path.
+    train_id = req.get("train_id")
+    if train_id is not None:
+        _require(isinstance(train_id, str) and bool(_SAFE_OUTPUT_NAME.match(train_id)),
+                 "train_id is not a safe token")
+
     # ---- paths (containment-checked) ------------------------------------------------
     dataset_dir = _validate_under(req.get("dataset_dir", ""), (config.HANDOFF_ROOT,), "dataset_dir")
     output_dir = _validate_under(req.get("output_dir", ""), (config.HANDOFF_ROOT,), "output_dir")
@@ -103,17 +111,19 @@ def validate_request(req: dict) -> dict:
         "dataset_dir": str(dataset_dir),
         "output_dir": str(output_dir),
         "base_model_path": str(base_model_path),
+        "train_id": train_id,
     }
 
 
-def published_relative_path(output_dir: str, output_name: str) -> str:
+def published_relative_path(output_dir: str, output_name: str, train_id: str | None = None) -> str:
     """The ComfyUI-relative loras path for a succeeded LoRA (Phase 2 publish step).
 
-    Derives {train_id} from the handoff layout `HANDOFF_ROOT/{train_id}/output` — i.e. the
-    name of the dir the LoRA was written into. Returns e.g. `trained/392cf898ac03/name.safetensors`,
+    Uses the explicit `train_id` (arbo now sends it — decoupled from the path layout); falls
+    back to deriving it from the handoff layout `HANDOFF_ROOT/{train_id}/output` (the name of the
+    dir the LoRA was written into) when absent. Returns e.g. `trained/392cf898ac03/name.safetensors`,
     the exact string a ComfyUI `LoraLoader.lora_name` widget takes. Pure — no filesystem touch."""
-    train_id = Path(output_dir).parent.name
-    return f"{config.PUBLISH_SUBDIR}/{train_id}/{output_name}.safetensors"
+    tid = train_id or Path(output_dir).parent.name
+    return f"{config.PUBLISH_SUBDIR}/{tid}/{output_name}.safetensors"
 
 
 def build_command(req: dict) -> tuple[list[str], dict[str, str], dict]:
diff --git a/services/lora-training-worker/worker/jobs.py b/services/lora-training-worker/worker/jobs.py
index 8f2e790..bbd8fd1 100644
--- a/services/lora-training-worker/worker/jobs.py
+++ b/services/lora-training-worker/worker/jobs.py
@@ -298,7 +298,9 @@ class JobManager:
         if not job.lora_path:
             return
         try:
-            rel = published_relative_path(job.params["output_dir"], job.params["output_name"])
+            rel = published_relative_path(
+                job.params["output_dir"], job.params["output_name"], job.params.get("train_id")
+            )
             dest = config.LORAS_PUBLISH_ROOT / rel
             dest.parent.mkdir(parents=True, exist_ok=True)
             try: