Harness foundation: INTENT, ADR-001, architecture, prototype adoption

- INTENT.md: three-layer model (blueprint/instance/harness), single
  shared runtime, never-become boundaries
- ADR-001 (accepted): DEC-2026-002 resolution — one harness repo for
  all projects; instances are declarative state in consuming repos
- docs/architecture.md: components, contracts (manifest, tool
  profiles, completion events, credential lanes), deployment shape
- agent_harness/: executor-worker prototype adopted and renamed
  (6/6 tests green); HARNESS-WP-0001 initial workplan (7 tasks)

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

tests/test_runner.py

@@ -0,0 +1,88 @@
+from __future__ import annotations
+
+import subprocess
+from pathlib import Path
+
+import pytest
+
+from agent_harness.runner import RunResult, run_task
+from agent_harness.taskspec import TaskSpec, TaskSpecError
+
+
+def _make_repo(tmp_path: Path) -> Path:
+    repo = tmp_path / "sandbox"
+    repo.mkdir()
+    subprocess.run(["git", "init", "-q"], cwd=repo, check=True)
+    (repo / "README.md").write_text("sandbox\n")
+    subprocess.run(["git", "add", "."], cwd=repo, check=True)
+    subprocess.run(
+        ["git", "-c", "user.email=t@t", "-c", "user.name=t", "commit", "-qm", "init"],
+        cwd=repo,
+        check=True,
+    )
+    return repo
+
+
+class CommittingAdapter:
+    """Fake adapter that simulates a session which commits."""
+
+    def __init__(self, repo: Path):
+        self.repo = repo
+        self.prompts: list[str] = []
+
+    def execute_prompt(self, prompt, config):
+        self.prompts.append(prompt)
+        (self.repo / "HELLO.md").write_text("hello\n")
+        subprocess.run(["git", "add", "."], cwd=self.repo, check=True)
+        subprocess.run(
+            ["git", "-c", "user.email=t@t", "-c", "user.name=t", "commit", "-qm", "task done"],
+            cwd=self.repo,
+            check=True,
+        )
+        from llm_connect.models import LLMResponse
+
+        return LLMResponse(content="done", model="fake", usage={}, finish_reason="stop")
+
+
+class IdleAdapter:
+    def execute_prompt(self, prompt, config):
+        from llm_connect.models import LLMResponse
+
+        return LLMResponse(content="nothing to do", model="fake", usage={}, finish_reason="stop")
+
+
+def _spec(repo: Path) -> TaskSpec:
+    return TaskSpec(title="write hello", description="create HELLO.md", target_repo=repo)
+
+
+def test_run_task_success_when_session_commits(tmp_path) -> None:
+    repo = _make_repo(tmp_path)
+    adapter = CommittingAdapter(repo)
+
+    result = run_task(_spec(repo), adapter=adapter, report_to_hub=False)
+
+    assert isinstance(result, RunResult)
+    assert result.ok is True
+    assert result.committed is True
+    assert result.head_before != result.head_after
+    assert "write hello" in adapter.prompts[0]
+    assert "Never push" in adapter.prompts[0]
+
+
+def test_run_task_fails_without_commit(tmp_path) -> None:
+    repo = _make_repo(tmp_path)
+
+    result = run_task(_spec(repo), adapter=IdleAdapter(), report_to_hub=False)
+
+    assert result.ok is False
+    assert result.committed is False
+    assert result.reason == "session completed without committing"
+
+
+def test_taskspec_rejects_non_repo(tmp_path) -> None:
+    spec_file = tmp_path / "task.json"
+    spec_file.write_text(
+        '{"title": "x", "description": "y", "target_repo": "%s"}' % tmp_path
+    )
+    with pytest.raises(TaskSpecError, match="not a git repository"):
+        TaskSpec.from_file(spec_file)