emrg: fix flaky install-info.json read — guarded parse + atomic write

Agent.md

@@ -93,7 +93,7 @@ Community needs voiced in HN agent-UI discussions map directly to EMRG's design:
 pkill -f "emrg.server"; rm -f ~/.emrg/emrgd.port; python -m emrg
 ```
 
-Python: `uv run pytest tests/ -v` (597) — import check: `uv run python -c "from emrg.client.app import run_client"`
+Python: `uv run pytest tests/ -v` (599) — import check: `uv run python -c "from emrg.client.app import run_client"`
 GUI: `cd emrg/gui && npm test` (93: 22 daemon_client + 22 app-commands + 24 renderer smoke + 15 i18n + 7 integration + 3 commands) — syntax: `node --check main.js preload.js daemon_client.js renderer/js/*.js`
 CI: `uv run pytest` + GUI tests + **actionlint workflow lint** (`rhysd/actionlint@v1.7.12` gate, #444 — workflow 解析错误在 PR CI 即失败，如 `if:` secrets 上下文)
 Re-trigger: `scripts/re-trigger-ci.sh [branch]` (workflow_dispatch, #527 — 替代空 commit 重触发：Actions outage 会整段丢弃 push 事件，dispatch 走 API 路径不受影响)

README.cn.md

@@ -274,7 +274,7 @@ EMRG 不只是追赶——它自己追上来。
 git clone https://github.com/argszero/emrg.git
 cd emrg
 uv sync              # 安装依赖
-uv run pytest tests/ -v   # 跑测试（当前 597 项）
+uv run pytest tests/ -v   # 跑测试（当前 599 项）
 uv run python -m emrg     # 启动 TUI
 # CI 含 actionlint workflow 门禁（#444）：workflow 解析错误在 PR 即失败
 

README.md

@@ -273,7 +273,7 @@ EMRG doesn't just keep up — it catches up on its own.
 git clone https://github.com/argszero/emrg.git
 cd emrg
 uv sync              # install deps
-uv run pytest tests/ -v   # run tests (currently 597 items)
+uv run pytest tests/ -v   # run tests (currently 599 items)
 uv run python -m emrg     # launch TUI
 # CI includes actionlint workflow gate (#444): workflow parse errors fail PR CI
 

emrg/server/git_utils.py

@@ -172,15 +172,25 @@ def _cache_tool_paths(git: str, gh: str) -> None:
     Also persists the EMRG repo URL (``repo``) so the evolution workspace
     self-heal (rant 2026-08-06T20:42:05) can clone on demand without
     hardcoding — packaged installs have no git remote to detect.
+
+    The write is atomic (temp file + os.replace) so concurrent readers
+    never observe a partially-written file; the read is guarded like
+    ``_cached_tool_path`` so a corrupt/partial cache (e.g. a crashed or
+    concurrent writer) degrades to an empty dict instead of raising
+    JSONDecodeError (observed as a flaky test_daemon failure when the
+    live daemon rewrote install-info.json mid-suite).
     """
     try:
         data = {}
         if INSTALL_INFO.exists():
-            data = json.loads(INSTALL_INFO.read_text(encoding="utf-8"))
+            try:
+                data = json.loads(INSTALL_INFO.read_text(encoding="utf-8"))
+            except (OSError, json.JSONDecodeError, AttributeError):
+                data = {}
         data.update({"git_path": git, "gh_path": gh, "repo": "https://github.com/argszero/emrg.git"})
-        INSTALL_INFO.write_text(
-            json.dumps(data, ensure_ascii=False, indent=2), encoding="utf-8"
-        )
+        tmp = INSTALL_INFO.with_name(INSTALL_INFO.name + ".tmp")
+        tmp.write_text(json.dumps(data, ensure_ascii=False, indent=2), encoding="utf-8")
+        os.replace(tmp, INSTALL_INFO)
     except OSError:
         pass
 

tests/test_git_utils.py

@@ -115,6 +115,46 @@ def test_cache_tool_paths_preserves_existing_fields(tmp_path, monkeypatch):
     assert data["repo"] == "https://github.com/argszero/emrg.git"
 
 
+def test_cache_tool_paths_tolerates_corrupt_cache(tmp_path, monkeypatch):
+    """A corrupt/partial install-info.json must not raise — degrades to {}.
+
+    Regression for the flaky test_daemon::test_build_prompt_with_project
+    (json.decoder.JSONDecodeError): the live daemon rewrites this shared
+    file non-atomically; a concurrent reader could catch a partial write.
+    """
+    from emrg.server import git_utils as mod
+    import json as _json
+
+    info = tmp_path / "install-info.json"
+    info.write_text('{"git_path": "/partial', encoding="utf-8")  # truncated JSON
+    monkeypatch.setattr(mod, "INSTALL_INFO", info)
+
+    mod._cache_tool_paths("/usr/bin/git", "/usr/bin/gh")  # must not raise
+
+    data = _json.loads(info.read_text(encoding="utf-8"))
+    assert data["git_path"] == "/usr/bin/git"
+    assert data["repo"] == "https://github.com/argszero/emrg.git"
+
+
+def test_cache_tool_paths_atomic_write_no_temp_leftover(tmp_path, monkeypatch):
+    """Write is atomic: target is valid JSON and no .tmp file remains."""
+    from emrg.server import git_utils as mod
+    import json as _json
+
+    info = tmp_path / "install-info.json"
+    info.write_text(
+        _json.dumps({"custom": "old"}), encoding="utf-8"
+    )
+    monkeypatch.setattr(mod, "INSTALL_INFO", info)
+
+    mod._cache_tool_paths("/usr/bin/git", "/usr/bin/gh")
+
+    assert not (tmp_path / "install-info.json.tmp").exists()
+    data = _json.loads(info.read_text(encoding="utf-8"))
+    assert data["git_path"] == "/usr/bin/git"
+    assert data["custom"] == "old"
+
+
 # ── no_prompt_env / parse_gh_auth_user (rant 2026-08-07T10:17:27) ──