Add ReinOpenWeights adapter, closing GLAS-WP-0001-T05

glas_harness/reins/rein_openweights.py implements the Rein ABC by
shelling out to `rein-openweights run --task-file ... --no-hub
[--model ...]`, mirroring reins/rein_aharness.py exactly. Factored the
duplicated git_head/write_task_file logic into reins/_shared.py, used
by both adapters now. registry/reins/rein-openweights.yaml flipped to
status: implemented. 8 new tests (mocked subprocess), 18/18 passing.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

tests/test_rein_aharness.py

@@ -80,8 +80,10 @@ def test_end_session_detects_new_commit(tmp_path) -> None:
     subprocess.run(["git", "init", "-q"], cwd=repo, check=True)
     subprocess.run(["git", "commit", "-q", "--allow-empty", "-m", "init"], cwd=repo, check=True)
 
+    from glas_harness.reins._shared import git_head
+
     rein = ReinAharness()
-    head_before = rein._git_head(str(repo))
+    head_before = git_head(str(repo))
 
     subprocess.run(["git", "commit", "-q", "--allow-empty", "-m", "task"], cwd=repo, check=True)
 
@@ -96,8 +98,10 @@ def test_end_session_no_new_commit(tmp_path) -> None:
     subprocess.run(["git", "init", "-q"], cwd=repo, check=True)
     subprocess.run(["git", "commit", "-q", "--allow-empty", "-m", "init"], cwd=repo, check=True)
 
+    from glas_harness.reins._shared import git_head
+
     rein = ReinAharness()
-    head = rein._git_head(str(repo))
+    head = git_head(str(repo))
 
     summary = rein.end_session({"target_repo": str(repo), "head_before": head})
     assert summary["committed"] == "False"

tests/test_rein_openweights.py

@@ -0,0 +1,106 @@
+import json
+import subprocess
+from unittest.mock import MagicMock, patch
+
+import pytest
+
+from glas_harness.contract import Rein, SandboxHandle, ToolCall
+from glas_harness.reins.rein_openweights import ReinOpenWeights, ReinOpenWeightsNotInstalled
+
+
+def test_is_rein_subclass() -> None:
+    assert issubclass(ReinOpenWeights, Rein)
+
+
+def test_bin_raises_if_not_installed() -> None:
+    rein = ReinOpenWeights(cli_bin="does-not-exist-binary")
+    with pytest.raises(ReinOpenWeightsNotInstalled):
+        rein._bin()
+
+
+def test_start_session_writes_task_file_and_captures_head(tmp_path) -> None:
+    repo = tmp_path / "repo"
+    repo.mkdir()
+    subprocess.run(["git", "init", "-q"], cwd=repo, check=True)
+    subprocess.run(["git", "commit", "-q", "--allow-empty", "-m", "init"], cwd=repo, check=True)
+
+    rein = ReinOpenWeights()
+    sandbox = SandboxHandle(sandbox_id="abc", host="localhost", reachability={"workspace_dir": str(repo)})
+    session = rein.start_session(
+        profile={"id": "harness.agent-dev-local"},
+        inputs={"title": "t", "description": "d"},
+        sandbox=sandbox,
+    )
+
+    assert session["target_repo"] == str(repo)
+    assert session["head_before"]
+    task_spec = json.loads(open(session["task_file"]).read())
+    assert task_spec["title"] == "t"
+    assert task_spec["target_repo"] == str(repo)
+
+
+def test_start_session_requires_resolvable_target_repo() -> None:
+    rein = ReinOpenWeights()
+    sandbox = SandboxHandle(sandbox_id="abc", host="localhost", reachability={})
+    with pytest.raises(ValueError, match="target_repo"):
+        rein.start_session(profile={}, inputs={"title": "t", "description": "d"}, sandbox=sandbox)
+
+
+def test_dispatch_tool_invokes_rein_openweights_cli() -> None:
+    rein = ReinOpenWeights()
+    session = {"task_file": "/tmp/task.json"}
+
+    fake_result = MagicMock(returncode=0, stdout="ok", stderr="")
+    with patch.object(rein, "_bin", return_value="/usr/bin/rein-openweights"):
+        with patch("glas_harness.reins.rein_openweights.subprocess.run", return_value=fake_result) as run:
+            result = rein.dispatch_tool(session, ToolCall(name="run_task"))
+
+    argv = run.call_args.args[0]
+    assert argv[:3] == ["/usr/bin/rein-openweights", "run", "--task-file"]
+    assert "--no-hub" in argv
+    assert result.ok is True
+    assert result.output == "ok"
+
+
+def test_dispatch_tool_passes_model_when_set() -> None:
+    rein = ReinOpenWeights(model="meta-llama/llama-3.1-70b-instruct")
+    session = {"task_file": "/tmp/task.json"}
+    fake_result = MagicMock(returncode=0, stdout="ok", stderr="")
+
+    with patch.object(rein, "_bin", return_value="/usr/bin/rein-openweights"):
+        with patch("glas_harness.reins.rein_openweights.subprocess.run", return_value=fake_result) as run:
+            rein.dispatch_tool(session, ToolCall(name="run_task"))
+
+    argv = run.call_args.args[0]
+    assert "--model" in argv
+    assert "meta-llama/llama-3.1-70b-instruct" in argv
+
+
+def test_dispatch_tool_reports_failure() -> None:
+    rein = ReinOpenWeights()
+    session = {"task_file": "/tmp/task.json"}
+
+    fake_result = MagicMock(returncode=1, stdout="", stderr="boom")
+    with patch.object(rein, "_bin", return_value="/usr/bin/rein-openweights"):
+        with patch("glas_harness.reins.rein_openweights.subprocess.run", return_value=fake_result):
+            result = rein.dispatch_tool(session, ToolCall(name="run_task"))
+
+    assert result.ok is False
+    assert result.error == "boom"
+
+
+def test_end_session_detects_new_commit(tmp_path) -> None:
+    repo = tmp_path / "repo"
+    repo.mkdir()
+    subprocess.run(["git", "init", "-q"], cwd=repo, check=True)
+    subprocess.run(["git", "commit", "-q", "--allow-empty", "-m", "init"], cwd=repo, check=True)
+
+    rein = ReinOpenWeights()
+    from glas_harness.reins._shared import git_head
+
+    head_before = git_head(str(repo))
+    subprocess.run(["git", "commit", "-q", "--allow-empty", "-m", "task"], cwd=repo, check=True)
+
+    summary = rein.end_session({"target_repo": str(repo), "head_before": head_before})
+    assert summary["committed"] == "True"
+    assert summary["commit_sha"] != head_before