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+# Plugin Error Checking Implementation Plan
+
+> **For agentic workers:** REQUIRED SUB-SKILL: Use superpowers:subagent-driven-development (recommended) or superpowers:executing-plans to implement this plan task-by-task. Steps use checkbox (`- [ ]`) syntax for tracking.
+
+**Goal:** Improve plugin error checking in hbc, especially for nagios_runner, and fix logger messages silently discarded in daemon mode.
+
+**Architecture:** Three focused changes across three files: (1) `hbd/client/plugin.py` gains a `skip_reason` attribute on Plugin and updated PluginLoader messaging; (2) `hbd/client/plugins/nagios_runner.py` gains async subprocess execution, stderr capture, signal-killed process handling, and init-time command path validation; (3) `hbd/client/main.py` gains proper post-fork logging reconfiguration to syslog.
+
+**Tech Stack:** Python 3.11+, asyncio, `logging.handlers.SysLogHandler`, pytest
+
+---
+
+## File Map
+
+| Action | Path | What changes |
+|---|---|---|
+| Modify | `hbd/client/plugin.py` | `Plugin.__init__` gains `skip_reason`; `PluginLoader` checks it |
+| Modify | `hbd/client/plugins/nagios_runner.py` | async subprocess, stderr, signal codes, init validation, `skip_reason` |
+| Modify | `hbd/client/main.py` | `_reconfigure_logging_for_daemon()` helper; remove redundant syslog calls |
+| Create | `tests/test_plugin.py` | PluginLoader messaging tests |
+| Create | `tests/test_nagios_runner.py` | NagiosRunnerPlugin behaviour tests |
+
+Run tests throughout with:
+```bash
+python -m pytest tests/test_plugin.py tests/test_nagios_runner.py -v
+```
+
+---
+
+## Task 1: Plugin.skip_reason + PluginLoader messaging
+
+**Files:**
+- Modify: `hbd/client/plugin.py:40-48` (Plugin.__init__)
+- Modify: `hbd/client/plugin.py:369-381` (PluginLoader.load_from_directory)
+- Create: `tests/test_plugin.py`
+
+- [ ] **Step 1: Write failing tests**
+
+Create `tests/test_plugin.py`:
+
+```python
+import asyncio
+import logging
+import textwrap
+
+from hbd.client.plugin import Plugin, PluginLoader, PluginRegistry
+
+
+def test_plugin_skip_reason_defaults_none(tmp_path):
+    plugin_code = textwrap.dedent("""
+        from hbd.client.plugin import MonitorPlugin
+
+        class MinimalPlugin(MonitorPlugin):
+            name = "minimal"
+            version = "1.0.0"
+            interval = 60
+
+            async def initialize(self):
+                return True
+
+            async def _collect_metrics(self):
+                return {}
+    """)
+    (tmp_path / "minimal.py").write_text(plugin_code)
+    registry = PluginRegistry()
+    loader = PluginLoader(registry)
+    asyncio.run(loader.load_from_directory(tmp_path))
+    plugin = registry.get("minimal")
+    assert plugin is not None
+    assert plugin.skip_reason is None
+
+
+def test_loader_logs_info_when_skip_reason_set(tmp_path, caplog):
+    plugin_code = textwrap.dedent("""
+        from hbd.client.plugin import MonitorPlugin
+
+        class SkippablePlugin(MonitorPlugin):
+            name = "skippable"
+            version = "1.0.0"
+            interval = 60
+
+            async def initialize(self):
+                self.skip_reason = "not configured in yaml"
+                return False
+
+            async def _collect_metrics(self):
+                return {}
+    """)
+    (tmp_path / "skippable.py").write_text(plugin_code)
+    registry = PluginRegistry()
+    loader = PluginLoader(registry)
+
+    with caplog.at_level(logging.INFO, logger="plugin.loader"):
+        count = asyncio.run(loader.load_from_directory(tmp_path))
+
+    assert count == 0
+    assert any("skipped: not configured in yaml" in r.message for r in caplog.records)
+    assert not any("failed initialization" in r.message for r in caplog.records)
+
+
+def test_loader_logs_warning_when_no_skip_reason(tmp_path, caplog):
+    plugin_code = textwrap.dedent("""
+        from hbd.client.plugin import MonitorPlugin
+
+        class FailPlugin(MonitorPlugin):
+            name = "fail"
+            version = "1.0.0"
+            interval = 60
+
+            async def initialize(self):
+                return False
+
+            async def _collect_metrics(self):
+                return {}
+    """)
+    (tmp_path / "fail_plugin.py").write_text(plugin_code)
+    registry = PluginRegistry()
+    loader = PluginLoader(registry)
+
+    with caplog.at_level(logging.WARNING, logger="plugin.loader"):
+        count = asyncio.run(loader.load_from_directory(tmp_path))
+
+    assert count == 0
+    assert any("failed initialization" in r.message for r in caplog.records)
+```
+
+- [ ] **Step 2: Run tests to verify they fail**
+
+```bash
+python -m pytest tests/test_plugin.py -v
+```
+Expected: `test_plugin_skip_reason_defaults_none` FAILS (attribute missing), others may error.
+
+- [ ] **Step 3: Add `skip_reason` to `Plugin.__init__`**
+
+In `hbd/client/plugin.py`, in `Plugin.__init__` (around line 46), add one line:
+
+```python
+def __init__(self, config: Optional[Dict[str, Any]] = None):
+    self.config = config or {}
+    self.logger = logging.getLogger(f"plugin.{self.name}")
+    self._initialized = False
+    self.skip_reason: Optional[str] = None
+```
+
+- [ ] **Step 4: Update PluginLoader messaging**
+
+In `hbd/client/plugin.py`, replace the `if not initialized:` block (around line 372):
+
+```python
+                    if not initialized:
+                        if plugin.skip_reason:
+                            self.logger.info(
+                                f"Plugin {plugin.name} skipped: {plugin.skip_reason}"
+                            )
+                        else:
+                            self.logger.warning(
+                                f"Plugin {plugin.name} failed initialization, skipping"
+                            )
+                        continue
+```
+
+- [ ] **Step 5: Run tests to verify they pass**
+
+```bash
+python -m pytest tests/test_plugin.py -v
+```
+Expected: all 3 tests PASS.
+
+- [ ] **Step 6: Commit**
+
+```bash
+git add hbd/client/plugin.py tests/test_plugin.py
+git commit -m "feat: add skip_reason to Plugin; improve PluginLoader init messaging"
+```
+
+---
+
+## Task 2: NagiosRunnerPlugin — skip_reason when no commands
+
+**Files:**
+- Modify: `hbd/client/plugins/nagios_runner.py:88-105` (initialize)
+- Modify: `tests/test_nagios_runner.py` (create)
+
+- [ ] **Step 1: Write failing test**
+
+Create `tests/test_nagios_runner.py`:
+
+```python
+import asyncio
+import logging
+import os
+import stat
+
+import pytest
+
+from hbd.client.plugins.nagios_runner import (
+    NagiosRunnerPlugin,
+    NAGIOS_OK,
+    NAGIOS_WARNING,
+    NAGIOS_CRITICAL,
+    NAGIOS_UNKNOWN,
+)
+
+
+def test_no_commands_sets_skip_reason():
+    plugin = NagiosRunnerPlugin(config={"commands": []})
+    result = asyncio.run(plugin.initialize())
+    assert result is False
+    assert plugin.skip_reason is not None
+    assert "nagios_runner.commands" in plugin.skip_reason
+```
+
+- [ ] **Step 2: Run test to verify it fails**
+
+```bash
+python -m pytest tests/test_nagios_runner.py::test_no_commands_sets_skip_reason -v
+```
+Expected: FAIL — `plugin.skip_reason` is `None`.
+
+- [ ] **Step 3: Set skip_reason in NagiosRunnerPlugin.initialize()**
+
+In `hbd/client/plugins/nagios_runner.py`, replace the early-return block in `initialize()` (around line 96):
+
+```python
+        if not self.commands:
+            self.skip_reason = "no commands configured (add nagios_runner.commands to config)"
+            self.logger.info("No Nagios commands configured")
+            return False
+```
+
+- [ ] **Step 4: Run test to verify it passes**
+
+```bash
+python -m pytest tests/test_nagios_runner.py::test_no_commands_sets_skip_reason -v
+```
+Expected: PASS.
+
+- [ ] **Step 5: Commit**
+
+```bash
+git add hbd/client/plugins/nagios_runner.py tests/test_nagios_runner.py
+git commit -m "feat: set skip_reason on nagios_runner when no commands configured"
+```
+
+---
+
+## Task 3: NagiosRunnerPlugin — async subprocess, stderr capture, negative return codes
+
+**Files:**
+- Modify: `hbd/client/plugins/nagios_runner.py` (imports + `_run_nagios_plugin`)
+- Modify: `tests/test_nagios_runner.py`
+
+- [ ] **Step 1: Write failing tests**
+
+Append to `tests/test_nagios_runner.py`:
+
+```python
+def test_stderr_used_when_stdout_empty(tmp_path):
+    script = tmp_path / "check_err.sh"
+    script.write_text("#!/bin/sh\necho 'error from stderr' >&2\nexit 2\n")
+    script.chmod(script.stat().st_mode | stat.S_IEXEC)
+
+    config = {"commands": [{"name": "t", "command": str(script)}], "timeout": 5}
+    plugin = NagiosRunnerPlugin(config=config)
+    asyncio.run(plugin.initialize())
+    data = asyncio.run(plugin._collect_metrics())
+
+    assert "error from stderr" in data["t_output"]
+    assert data["t_status_code"] == NAGIOS_CRITICAL
+
+
+def test_stderr_appended_when_both_present(tmp_path):
+    script = tmp_path / "check_both.sh"
+    script.write_text("#!/bin/sh\necho 'OK - all good'\necho 'extra detail' >&2\nexit 0\n")
+    script.chmod(script.stat().st_mode | stat.S_IEXEC)
+
+    config = {"commands": [{"name": "t", "command": str(script)}], "timeout": 5}
+    plugin = NagiosRunnerPlugin(config=config)
+    asyncio.run(plugin.initialize())
+    data = asyncio.run(plugin._collect_metrics())
+
+    assert "OK - all good" in data["t_output"]
+    assert "extra detail" in data["t_output"]
+    assert data["t_status_code"] == NAGIOS_OK
+
+
+def test_negative_returncode_maps_to_unknown():
+    # kill -9 $$ kills the shell itself; asyncio sees returncode -9
+    config = {"commands": [{"name": "t", "command": "kill -9 $$"}], "timeout": 5}
+    plugin = NagiosRunnerPlugin(config=config)
+    asyncio.run(plugin.initialize())
+    data = asyncio.run(plugin._collect_metrics())
+
+    assert data["t_status_code"] == NAGIOS_UNKNOWN
+    assert "signal" in data["t_output"].lower()
+```
+
+- [ ] **Step 2: Run tests to verify they fail**
+
+```bash
+python -m pytest tests/test_nagios_runner.py::test_stderr_used_when_stdout_empty \
+    tests/test_nagios_runner.py::test_stderr_appended_when_both_present \
+    tests/test_nagios_runner.py::test_negative_returncode_maps_to_unknown -v
+```
+Expected: all FAIL — current implementation ignores stderr and doesn't handle negative codes.
+
+- [ ] **Step 3: Update imports in nagios_runner.py**
+
+Replace the import block at the top of `hbd/client/plugins/nagios_runner.py`:
+
+```python
+import asyncio
+import os
+import re
+from typing import Any, Dict, List, Optional, Tuple
+
+from hbd.client.plugin import MonitorPlugin
+```
+
+(Remove `import subprocess`; add `import asyncio` and `import os`.)
+
+- [ ] **Step 4: Upgrade collection log level from DEBUG to INFO**
+
+In `hbd/client/plugins/nagios_runner.py`, in `_collect_metrics()`, change the debug log (around line 144) so results are visible at INFO level:
+
+```python
+                self.logger.info(
+                    f"Executed {name}: {STATUS_NAMES.get(status_code, 'UNKNOWN')} - {output[:50]}"
+                )
+```
+
+- [ ] **Step 5: Replace `_run_nagios_plugin` with async implementation**
+
+Replace the entire `_run_nagios_plugin` method in `hbd/client/plugins/nagios_runner.py`:
+
+```python
+    async def _run_nagios_plugin(
+        self,
+        command: str
+    ) -> Tuple[int, str, Dict[str, Any]]:
+        """Execute a Nagios plugin and parse its output."""
+        try:
+            proc = await asyncio.create_subprocess_shell(
+                command,
+                stdout=asyncio.subprocess.PIPE,
+                stderr=asyncio.subprocess.PIPE,
+            )
+            try:
+                stdout_bytes, stderr_bytes = await asyncio.wait_for(
+                    proc.communicate(), timeout=self.timeout
+                )
+            except asyncio.TimeoutError:
+                proc.kill()
+                await proc.communicate()
+                self.logger.error(f"Command timed out: {command}")
+                return NAGIOS_UNKNOWN, f"Command timed out after {self.timeout}s", {}
+
+            status_code = proc.returncode
+
+            if status_code < 0:
+                return NAGIOS_UNKNOWN, f"Process killed by signal {-status_code}", {}
+
+            if status_code > 3:
+                status_code = NAGIOS_UNKNOWN
+
+            stdout = stdout_bytes.decode(errors="replace").strip()
+            stderr = stderr_bytes.decode(errors="replace").strip()
+
+            # Parse perfdata from stdout before mixing in stderr
+            perfdata = self._parse_perfdata(stdout)
+
+            # Build status message
+            status_part = stdout.split('|')[0].strip() if '|' in stdout else stdout
+
+            if not stdout and stderr:
+                output_msg = stderr
+            elif stdout and stderr:
+                output_msg = f"{status_part} [stderr: {stderr}]"
+            else:
+                output_msg = status_part
+
+            return status_code, output_msg, perfdata
+
+        except Exception as e:
+            self.logger.error(f"Error executing command: {e}")
+            return NAGIOS_UNKNOWN, f"Execution error: {str(e)}", {}
+```
+
+Also remove the now-unused `self.shell` line from `__init__` (the `shell` config key is no longer used since `create_subprocess_shell` always uses a shell):
+
+In `NagiosRunnerPlugin.__init__`, remove:
+```python
+        self.shell: bool = config.get("shell", True) if config else True
+```
+
+- [ ] **Step 6: Run tests to verify they pass**
+
+```bash
+python -m pytest tests/test_nagios_runner.py -v
+```
+Expected: all tests PASS including the 3 new ones.
+
+- [ ] **Step 7: Commit**
+
+```bash
+git add hbd/client/plugins/nagios_runner.py tests/test_nagios_runner.py
+git commit -m "feat: async subprocess in nagios_runner with stderr capture and signal handling"
+```
+
+---
+
+## Task 4: NagiosRunnerPlugin — command path validation at init
+
+**Files:**
+- Modify: `hbd/client/plugins/nagios_runner.py` (initialize)
+- Modify: `tests/test_nagios_runner.py`
+
+- [ ] **Step 1: Write failing tests**
+
+Append to `tests/test_nagios_runner.py`:
+
+```python
+def test_absolute_path_not_found_warns(caplog):
+    fake_cmd = "/nonexistent_hbc_test_path/check_something"
+    config = {"commands": [{"name": "t", "command": fake_cmd}]}
+    plugin = NagiosRunnerPlugin(config=config)
+
+    with caplog.at_level(logging.WARNING, logger="plugin.nagios_runner"):
+        asyncio.run(plugin.initialize())
+
+    assert any("not found" in r.message for r in caplog.records)
+
+
+def test_absolute_path_not_executable_warns(caplog, tmp_path):
+    non_exec = tmp_path / "check_test"
+    non_exec.write_text("#!/bin/sh\necho OK\n")
+    non_exec.chmod(0o644)  # readable but not executable
+
+    config = {"commands": [{"name": "t", "command": str(non_exec)}]}
+    plugin = NagiosRunnerPlugin(config=config)
+
+    with caplog.at_level(logging.WARNING, logger="plugin.nagios_runner"):
+        asyncio.run(plugin.initialize())
+
+    assert any("not executable" in r.message for r in caplog.records)
+
+
+def test_relative_path_not_checked(caplog):
+    # Relative paths (resolved via PATH) must not generate warnings
+    config = {"commands": [{"name": "t", "command": "echo OK"}]}
+    plugin = NagiosRunnerPlugin(config=config)
+
+    with caplog.at_level(logging.WARNING, logger="plugin.nagios_runner"):
+        asyncio.run(plugin.initialize())
+
+    assert not any(
+        "not found" in r.message or "not executable" in r.message
+        for r in caplog.records
+    )
+```
+
+- [ ] **Step 2: Run tests to verify they fail**
+
+```bash
+python -m pytest tests/test_nagios_runner.py::test_absolute_path_not_found_warns \
+    tests/test_nagios_runner.py::test_absolute_path_not_executable_warns \
+    tests/test_nagios_runner.py::test_relative_path_not_checked -v
+```
+Expected: `test_absolute_path_not_found_warns` and `test_absolute_path_not_executable_warns` FAIL (no warnings logged); `test_relative_path_not_checked` may pass.
+
+- [ ] **Step 3: Add command path validation to `initialize()`**
+
+In `hbd/client/plugins/nagios_runner.py`, extend `initialize()` by adding validation after the existing "log each command" loop (after line 103, before `return True`):
+
+```python
+        # Validate absolute command paths early
+        for cmd_config in self.commands:
+            name = cmd_config.get("name", "unnamed")
+            command = cmd_config.get("command", "")
+            if not command:
+                continue
+            exe = command.split()[0]
+            if os.path.isabs(exe):
+                if not os.path.isfile(exe):
+                    self.logger.warning(
+                        f"Command '{name}': executable not found: {exe}"
+                    )
+                elif not os.access(exe, os.X_OK):
+                    self.logger.warning(
+                        f"Command '{name}': executable not executable: {exe}"
+                    )
+```
+
+- [ ] **Step 4: Run full test suite to verify all pass**
+
+```bash
+python -m pytest tests/test_plugin.py tests/test_nagios_runner.py -v
+```
+Expected: all tests PASS.
+
+- [ ] **Step 5: Commit**
+
+```bash
+git add hbd/client/plugins/nagios_runner.py tests/test_nagios_runner.py
+git commit -m "feat: validate absolute command paths at nagios_runner init"
+```
+
+---
+
+## Task 5: Daemon mode logging — route to syslog after fork
+
+**Files:**
+- Modify: `hbd/client/main.py` (new helper + updated daemon block)
+
+No automated test for daemonization itself (fork behaviour is hard to unit-test). Manual verification steps are provided below.
+
+- [ ] **Step 1: Add `_reconfigure_logging_for_daemon` helper**
+
+In `hbd/client/main.py`, add this function just before `def build_parser()` (around line 589):
+
+```python
+def _reconfigure_logging_for_daemon(log_level: int) -> None:
+    """Replace StreamHandlers (now writing to /dev/null) with a SysLogHandler."""
+    from logging.handlers import SysLogHandler
+
+    root = logging.getLogger()
+    for handler in root.handlers[:]:
+        root.removeHandler(handler)
+        handler.close()
+
+    try:
+        syslog_handler = SysLogHandler(
+            address="/dev/log",
+            facility=SysLogHandler.LOG_DAEMON,
+        )
+    except OSError:
+        syslog_handler = SysLogHandler(
+            address=("localhost", 514),
+            facility=SysLogHandler.LOG_DAEMON,
+        )
+        # Attach the fallback first so the warning reaches syslog
+        syslog_handler.setFormatter(
+            logging.Formatter("hbc[%(process)d]: %(name)s %(levelname)s: %(message)s")
+        )
+        root.addHandler(syslog_handler)
+        root.setLevel(log_level)
+        logging.warning("/dev/log not found, using syslog UDP localhost:514")
+        return
+
+    syslog_handler.setFormatter(
+        logging.Formatter("hbc[%(process)d]: %(name)s %(levelname)s: %(message)s")
+    )
+    root.addHandler(syslog_handler)
+    root.setLevel(log_level)
+```
+
+- [ ] **Step 2: Update the daemon block in `main()`**
+
+In `hbd/client/main.py`, replace the entire `if args.daemon:` block (lines 664–675):
+
+```python
+    if args.daemon:
+        print("Daemonizing...")
+        daemonize()
+        _reconfigure_logging_for_daemon(log_level)
+        logging.info(f"hbc starting, sending heartbeat to {', '.join(args.hosts)}")
+```
+
+This removes the `import syslog`, `syslog.openlog()`, and `syslog.syslog()` calls (now handled by the logging system) and removes the no-op second `logging.basicConfig()` call.
+
+- [ ] **Step 3: Run existing test suite to confirm no regressions**
+
+```bash
+python -m pytest tests/test_plugin.py tests/test_nagios_runner.py -v
+```
+Expected: all tests still PASS.
+
+- [ ] **Step 4: Manual smoke test — verify syslog output in daemon mode**
+
+```bash
+# In one terminal, tail syslog
+sudo journalctl -f -t hbc
+
+# In another terminal, start hbc in daemon mode (replace HOST with a real or dummy host)
+python -m hbd.client.main -d -v localhost
+
+# Expected in journalctl output:
+#   hbc[<pid>]: hbc.main INFO: Starting hbc for <hostname> -> ['localhost']
+#   hbc[<pid>]: hbc.main INFO: hbc starting, sending heartbeat to localhost
+#   hbc[<pid>]: plugin.loader INFO: ...
+
+# Stop the daemon
+pkill -f "hbd.client.main"
+```
+
+- [ ] **Step 5: Commit**
+
+```bash
+git add hbd/client/main.py
+git commit -m "fix: reconfigure logging to syslog after daemonize() instead of no-op basicConfig"
+```