feat(plugins): add optional-plugins/ discovery + langfuse_tracing as first official optional plugin

Introduces optional-plugins/ — a new category for plugins that ship with
the repo but are NOT auto-discovered. They live alongside the code but only
land in ~/.hermes/plugins/ (and thus get loaded) when the user explicitly
installs them.

Core changes:
- optional-plugins/observability/langfuse-tracing/ — langfuse tracing plugin
  (pre/post LLM + tool hooks, usage/cost normalization, fail-open when SDK
  missing). NOT in plugins/ so zero import overhead on devices that don't
  want it.
- hermes_cli/plugins_cmd.py — official install path: _resolve_official_plugin()
  recognises 'official/<category>/<name>' identifiers and copies from
  optional-plugins/ into ~/.hermes/plugins/ (no git clone, no network).
  _list_official_plugins() enumerates available optional plugins.
  cmd_list(available=True) shows not-yet-installed official plugins.
- hermes_cli/main.py — hermes plugins list --available flag
- hermes_cli/tools_config.py — Langfuse Observability in TOOL_CATEGORIES;
  post_setup handler installs the langfuse SDK and runs cmd_install()
- hermes_cli/config.py — Langfuse credentials in OPTIONAL_ENV_VARS;
  optional tuning keys in _EXTRA_ENV_KEYS

User flows:
  hermes plugins install official/observability/langfuse-tracing
  hermes plugins list --available
  hermes tools  (-> Langfuse Observability -> credentials -> auto-installs)

Closes #15764

hermes_cli/config.py

@@ -58,6 +58,16 @@ _EXTRA_ENV_KEYS = frozenset({
     "MATRIX_PASSWORD", "MATRIX_ENCRYPTION", "MATRIX_DEVICE_ID", "MATRIX_HOME_ROOM",
     "MATRIX_REQUIRE_MENTION", "MATRIX_FREE_RESPONSE_ROOMS", "MATRIX_AUTO_THREAD", "MATRIX_DM_AUTO_THREAD",
     "MATRIX_RECOVERY_KEY",
+    # Langfuse observability plugin — optional tuning keys + standard SDK vars
+    "HERMES_LANGFUSE_ENABLED",   # backward-compat env var (new: plugins.langfuse.enabled in config.yaml)
+    "HERMES_LANGFUSE_ENV",
+    "HERMES_LANGFUSE_RELEASE",
+    "HERMES_LANGFUSE_SAMPLE_RATE",
+    "HERMES_LANGFUSE_MAX_CHARS",
+    "HERMES_LANGFUSE_DEBUG",
+    "LANGFUSE_PUBLIC_KEY",
+    "LANGFUSE_SECRET_KEY",
+    "LANGFUSE_BASE_URL",
 })
 import yaml
 
@@ -1692,6 +1702,30 @@ OPTIONAL_ENV_VARS = {
         "category": "tool",
     },
 
+    # ── Langfuse observability ──
+    "HERMES_LANGFUSE_PUBLIC_KEY": {
+        "description": "Langfuse project public key (pk-lf-...)",
+        "prompt": "Langfuse public key",
+        "url": "https://cloud.langfuse.com",
+        "password": False,
+        "category": "tool",
+    },
+    "HERMES_LANGFUSE_SECRET_KEY": {
+        "description": "Langfuse project secret key (sk-lf-...)",
+        "prompt": "Langfuse secret key",
+        "url": "https://cloud.langfuse.com",
+        "password": True,
+        "category": "tool",
+    },
+    "HERMES_LANGFUSE_BASE_URL": {
+        "description": "Langfuse server URL (default: https://cloud.langfuse.com)",
+        "prompt": "Langfuse server URL (leave empty for cloud.langfuse.com)",
+        "url": None,
+        "password": False,
+        "category": "tool",
+        "advanced": True,
+    },
+
     # ── Messaging platforms ──
     "TELEGRAM_BOT_TOKEN": {
         "description": "Telegram bot token from @BotFather",

hermes_cli/main.py

@@ -9082,7 +9082,11 @@ Examples:
     )
     plugins_remove.add_argument("name", help="Plugin directory name to remove")
 
-    plugins_subparsers.add_parser("list", aliases=["ls"], help="List installed plugins")
+    plugins_list = plugins_subparsers.add_parser("list", aliases=["ls"], help="List installed plugins")
+    plugins_list.add_argument(
+        "--available", action="store_true",
+        help="Also show official optional plugins that are not yet installed",
+    )
 
     plugins_enable = plugins_subparsers.add_parser(
         "enable", help="Enable a disabled plugin"

hermes_cli/plugins_cmd.py

@@ -1,7 +1,13 @@
 """``hermes plugins`` CLI subcommand — install, update, remove, and list plugins.
 
-Plugins are installed from Git repositories into ``~/.hermes/plugins/``.
+Plugins can be installed from:
-Supports full URLs and ``owner/repo`` shorthand (resolves to GitHub).
+- Official optional plugins shipped with the repo: ``official/<category>/<name>``
+- Git repositories (full URL or ``owner/repo`` GitHub shorthand)
+
+Official plugins live in ``optional-plugins/`` inside the Hermes repo and are
+copied into ``~/.hermes/plugins/`` on install — no git clone needed, no network
+required. They are NOT auto-discovered from ``optional-plugins/``; only installed
+copies in ``~/.hermes/plugins/`` are loaded by Hermes.
 
 After install, if the plugin ships an ``after-install.md`` file it is
 rendered with Rich Markdown.  Otherwise a default confirmation is shown.
@@ -95,10 +101,80 @@ def _resolve_git_url(identifier: str) -> str:
 
     raise ValueError(
         f"Invalid plugin identifier: '{identifier}'. "
-        "Use a Git URL or owner/repo shorthand."
+        "Use 'official/<category>/<name>', a Git URL, or owner/repo shorthand."
     )
 
 
+def _optional_plugins_dir() -> Path:
+    """Return the optional-plugins/ directory shipped with the Hermes repo."""
+    return Path(__file__).resolve().parent.parent / "optional-plugins"
+
+
+def _resolve_official_plugin(identifier: str) -> Optional[Path]:
+    """If *identifier* is 'official/<category>/<name>', return its source path.
+
+    Returns ``None`` when the identifier is not in official format or the
+    plugin directory does not exist.
+    """
+    # Accept 'official/category/name' or just 'category/name' when the
+    # category/name path exists under optional-plugins/.
+    parts = identifier.strip("/").split("/")
+
+    # Strip leading 'official' prefix if present
+    if parts and parts[0] == "official":
+        parts = parts[1:]
+
+    if len(parts) < 1:
+        return None
+
+    base = _optional_plugins_dir()
+    # Try category/name  (2 parts) or bare name  (1 part)
+    for nparts in (2, 1):
+        if len(parts) < nparts:
+            continue
+        candidate = base.joinpath(*parts[-nparts:])
+        try:
+            resolved = candidate.resolve()
+            base_resolved = base.resolve()
+            resolved.relative_to(base_resolved)  # traversal guard
+        except (ValueError, OSError):
+            continue
+        if resolved.is_dir() and (
+            (resolved / "plugin.yaml").exists() or (resolved / "__init__.py").exists()
+        ):
+            return resolved
+
+    return None
+
+
+def _list_official_plugins() -> list[tuple[str, str]]:
+    """Return [(identifier, description), ...] for all official optional plugins."""
+    base = _optional_plugins_dir()
+    if not base.is_dir():
+        return []
+
+    results = []
+    for category_dir in sorted(base.iterdir()):
+        if not category_dir.is_dir() or category_dir.name.startswith("."):
+            continue
+        for plugin_dir in sorted(category_dir.iterdir()):
+            if not plugin_dir.is_dir() or plugin_dir.name.startswith("."):
+                continue
+            manifest_file = plugin_dir / "plugin.yaml"
+            desc = ""
+            if manifest_file.exists():
+                try:
+                    import yaml
+                    data = yaml.safe_load(manifest_file.read_text()) or {}
+                    desc = data.get("description", "")
+                except Exception:
+                    pass
+            identifier = f"official/{category_dir.name}/{plugin_dir.name}"
+            results.append((identifier, desc))
+
+    return results
+
+
 def _repo_name_from_url(url: str) -> str:
     """Extract the repo name from a Git URL for the plugin directory name."""
     # Strip trailing .git and slashes
@@ -296,7 +372,61 @@ def cmd_install(
     from rich.console import Console
 
     console = Console()
+    plugins_dir = _plugins_dir()
 
+    # ── Official optional plugins (no network, copied from optional-plugins/) ──
+    official_src = _resolve_official_plugin(identifier)
+    if official_src is not None:
+        manifest = _read_manifest(official_src)
+        plugin_name = manifest.get("name") or official_src.name
+        target = _sanitize_plugin_name(plugin_name, plugins_dir)
+
+        if target.exists():
+            if not force:
+                console.print(
+                    f"[red]Error:[/red] Plugin '{plugin_name}' already exists at {target}.\n"
+                    f"Use [bold]--force[/bold] to reinstall, or "
+                    f"[bold]hermes plugins update {plugin_name}[/bold] to update."
+                )
+                sys.exit(1)
+            console.print(f"[dim]  Removing existing {plugin_name}...[/dim]")
+            shutil.rmtree(target)
+
+        console.print(f"[dim]Installing {plugin_name} from official optional plugins...[/dim]")
+        shutil.copytree(str(official_src), str(target))
+
+        _copy_example_files(target, console)
+        _prompt_plugin_env_vars(manifest, console)
+        _display_after_install(target, identifier)
+
+        installed_name = manifest.get("name") or target.name
+        should_enable = enable
+        if should_enable is None:
+            if sys.stdin.isatty() and sys.stdout.isatty():
+                try:
+                    answer = input("  Enable now? [y/N] ").strip().lower()
+                    should_enable = answer in ("y", "yes")
+                except (EOFError, KeyboardInterrupt):
+                    should_enable = False
+            else:
+                should_enable = False
+
+        if should_enable:
+            enabled = _get_enabled_set()
+            disabled = _get_disabled_set()
+            enabled.add(installed_name)
+            disabled.discard(installed_name)
+            _save_enabled_set(enabled)
+            _save_disabled_set(disabled)
+            console.print(f"  [green]✓[/green] Plugin [bold]{installed_name}[/bold] enabled.")
+        else:
+            console.print(
+                f"  [dim]Plugin installed but not enabled. "
+                f"Run [bold]hermes plugins enable {installed_name}[/bold] to activate.[/dim]"
+            )
+        return
+
+    # ── Git URL / owner/repo install ──────────────────────────────────────────
     try:
         git_url = _resolve_git_url(identifier)
     except ValueError as e:
@@ -310,8 +440,6 @@ def cmd_install(
             "Consider using https:// or git@ for production installs."
         )
 
-    plugins_dir = _plugins_dir()
-
     # Clone into a temp directory first so we can read plugin.yaml for the name
     with tempfile.TemporaryDirectory() as tmp:
         tmp_target = Path(tmp) / "plugin"
@@ -696,16 +824,21 @@ def _discover_all_plugins() -> list:
     return list(seen.values())
 
 
-def cmd_list() -> None:
+def cmd_list(available: bool = False) -> None:
-    """List all plugins (bundled + user) with enabled/disabled state."""
+    """List all plugins (bundled + user) with enabled/disabled state.
+
+    When *available* is True, also show official optional plugins that are
+    not yet installed.
+    """
     from rich.console import Console
     from rich.table import Table
 
     console = Console()
     entries = _discover_all_plugins()
-    if not entries:
+    if not entries and not available:
         console.print("[dim]No plugins installed.[/dim]")
-        console.print("[dim]Install with:[/dim] hermes plugins install owner/repo")
+        console.print("[dim]Install with:[/dim] hermes plugins install official/<category>/<name>")
+        console.print("[dim]Browse available:[/dim] hermes plugins list --available")
         return
 
     enabled = _get_enabled_set()
@@ -734,6 +867,31 @@ def cmd_list() -> None:
     console.print("[dim]Enable/disable:[/dim] hermes plugins enable/disable <name>")
     console.print("[dim]Plugins are opt-in by default — only 'enabled' plugins load.[/dim]")
 
+    if available:
+        official = _list_official_plugins()
+        if official:
+            installed_names = {name for name, *_ in entries}
+            def _is_installed(ident: str) -> bool:
+                dirname = ident.rsplit("/", 1)[-1]
+                # Check both the directory name (langfuse-tracing) and
+                # common underscore variant (langfuse_tracing) since the
+                # installed plugin uses the manifest name, not the dir name.
+                return (dirname in installed_names
+                        or dirname.replace("-", "_") in installed_names)
+            not_installed = [(ident, desc) for ident, desc in official
+                             if not _is_installed(ident)]
+            if not_installed:
+                console.print()
+                avail_table = Table(title="Official optional plugins (not installed)", show_lines=False)
+                avail_table.add_column("Identifier", style="bold")
+                avail_table.add_column("Description")
+                for ident, desc in not_installed:
+                    avail_table.add_row(ident, desc)
+                console.print(avail_table)
+                console.print("[dim]Install:[/dim] hermes plugins install official/<category>/<name>")
+            else:
+                console.print("[dim]All official optional plugins are already installed.[/dim]")
+
 
 # ---------------------------------------------------------------------------
 # Provider plugin discovery helpers
@@ -1270,7 +1428,7 @@ def plugins_command(args) -> None:
     elif action == "disable":
         cmd_disable(args.name)
     elif action in ("list", "ls"):
-        cmd_list()
+        cmd_list(available=getattr(args, "available", False))
     elif action is None:
         cmd_toggle()
     else:

hermes_cli/tools_config.py

@@ -425,6 +425,31 @@ TOOL_CATEGORIES = {
             },
         ],
     },
+    "langfuse": {
+        "name": "Langfuse Observability",
+        "icon": "📊",
+        "providers": [
+            {
+                "name": "Langfuse Cloud",
+                "tag": "Hosted Langfuse (cloud.langfuse.com)",
+                "env_vars": [
+                    {"key": "HERMES_LANGFUSE_PUBLIC_KEY", "prompt": "Langfuse public key (pk-lf-...)", "url": "https://cloud.langfuse.com"},
+                    {"key": "HERMES_LANGFUSE_SECRET_KEY", "prompt": "Langfuse secret key (sk-lf-...)", "url": "https://cloud.langfuse.com"},
+                ],
+                "post_setup": "langfuse",
+            },
+            {
+                "name": "Langfuse Self-Hosted",
+                "tag": "Self-hosted Langfuse instance",
+                "env_vars": [
+                    {"key": "HERMES_LANGFUSE_PUBLIC_KEY", "prompt": "Langfuse public key (pk-lf-...)"},
+                    {"key": "HERMES_LANGFUSE_SECRET_KEY", "prompt": "Langfuse secret key (sk-lf-...)"},
+                    {"key": "HERMES_LANGFUSE_BASE_URL", "prompt": "Langfuse server URL (e.g. http://localhost:3000)", "default": "http://localhost:3000"},
+                ],
+                "post_setup": "langfuse",
+            },
+        ],
+    },
 }
 
 # Simple env-var requirements for toolsets NOT in TOOL_CATEGORIES.
@@ -567,6 +592,31 @@ def _run_post_setup(post_setup_key: str):
                 _print_info("      git submodule update --init --recursive")
                 _print_info('      uv pip install -e "./tinker-atropos"')
 
+    elif post_setup_key == "langfuse":
+        # Install the langfuse SDK.
+        try:
+            __import__("langfuse")
+            _print_success("    langfuse SDK already installed")
+        except ImportError:
+            import subprocess
+            _print_info("    Installing langfuse SDK...")
+            result = subprocess.run(
+                [sys.executable, "-m", "pip", "install", "langfuse", "--quiet"],
+                capture_output=True, text=True, timeout=120,
+            )
+            if result.returncode == 0:
+                _print_success("    langfuse SDK installed")
+            else:
+                _print_warning("    langfuse SDK install failed — run manually: pip install langfuse")
+        # Install and enable the official optional plugin into ~/.hermes/plugins/.
+        try:
+            from hermes_cli.plugins_cmd import cmd_install as _plugins_install
+            _plugins_install("official/observability/langfuse", enable=True)
+        except SystemExit:
+            pass  # cmd_install prints its own errors and calls sys.exit
+        _print_info("    Restart Hermes for tracing to take effect.")
+        _print_info("    Verify: hermes plugins list")
+
 
 # ─── Platform / Toolset Helpers ───────────────────────────────────────────────
 

optional-plugins/observability/langfuse/__init__.py

@@ -0,0 +1,875 @@
+"""langfuse — Hermes plugin for Langfuse observability.
+
+Traces Hermes conversations, LLM calls, and tool usage to Langfuse.
+Enable via ``hermes tools`` or by setting HERMES_LANGFUSE_ENABLED=true
+and the required credentials in ~/.hermes/.env.
+
+Required env vars (set via ``hermes tools`` or ~/.hermes/.env):
+  HERMES_LANGFUSE_ENABLED   - set to "true" to activate tracing
+  HERMES_LANGFUSE_PUBLIC_KEY  - Langfuse project public key (pk-lf-...)
+  HERMES_LANGFUSE_SECRET_KEY  - Langfuse project secret key (sk-lf-...)
+  HERMES_LANGFUSE_BASE_URL    - Langfuse server URL (default: https://cloud.langfuse.com)
+
+Optional env vars:
+  HERMES_LANGFUSE_ENV         - environment tag (e.g. "production", "local")
+  HERMES_LANGFUSE_RELEASE     - release/version tag
+  HERMES_LANGFUSE_SAMPLE_RATE - sampling rate 0.0–1.0 (default: 1.0)
+  HERMES_LANGFUSE_MAX_CHARS   - max chars per field (default: 12000)
+  HERMES_LANGFUSE_DEBUG       - set to "true" for verbose logging
+"""
+from __future__ import annotations
+
+import json
+import logging
+import os
+import re
+import threading
+import time
+from dataclasses import dataclass, field
+from typing import Any, Dict, Optional
+
+logger = logging.getLogger(__name__)
+
+try:
+    from langfuse import Langfuse, propagate_attributes
+except Exception:  # pragma: no cover - fail-open when optional dep is missing
+    Langfuse = None
+    propagate_attributes = None
+
+
+@dataclass
+class TraceState:
+    trace_id: str
+    root_ctx: Any
+    root_span: Any
+    generations: Dict[str, Any] = field(default_factory=dict)
+    tools: Dict[str, Any] = field(default_factory=dict)
+    turn_tool_calls: list[dict[str, Any]] = field(default_factory=list)
+    last_updated_at: float = field(default_factory=time.time)
+
+
+_STATE_LOCK = threading.Lock()
+_TRACE_STATE: Dict[str, TraceState] = {}
+_LANGFUSE_CLIENT = None
+_READ_FILE_LINE_RE = re.compile(r"^\s*(\d+)\|(.*)$")
+_READ_FILE_HEAD_LINES = 25
+_READ_FILE_TAIL_LINES = 15
+
+
+def _env(name: str, default: str = "") -> str:
+    return os.environ.get(name, default).strip()
+
+
+def _env_bool(*names: str) -> bool:
+    for name in names:
+        value = _env(name).lower()
+        if value:
+            return value in {"1", "true", "yes", "on"}
+    return False
+
+
+def _debug_enabled() -> bool:
+    return _env_bool("HERMES_LANGFUSE_DEBUG")
+
+
+def _debug(message: str) -> None:
+    if _debug_enabled():
+        logger.info("Langfuse tracing: %s", message)
+
+
+def _is_enabled() -> bool:
+    if Langfuse is None:
+        return False
+    # Primary activation path: config.yaml plugins.langfuse.enabled
+    try:
+        from hermes_cli.config import load_config
+        _cfg = load_config()
+        _plugin_cfg = _cfg.get("plugins", {})
+        if isinstance(_plugin_cfg, dict):
+            _lt_cfg = _plugin_cfg.get("langfuse", {})
+            if isinstance(_lt_cfg, dict) and "enabled" in _lt_cfg:
+                if not _lt_cfg["enabled"]:
+                    return False
+                # Explicit enabled=true in config — skip env-var check below
+                public_key = _env("HERMES_LANGFUSE_PUBLIC_KEY") or _env("LANGFUSE_PUBLIC_KEY")
+                secret_key = _env("HERMES_LANGFUSE_SECRET_KEY") or _env("LANGFUSE_SECRET_KEY")
+                return bool(public_key and secret_key)
+    except Exception:
+        pass
+    # Backward-compat path: HERMES_LANGFUSE_ENABLED env var (legacy .env installs)
+    if not _env_bool("HERMES_LANGFUSE_ENABLED"):
+        return False
+    public_key = _env("HERMES_LANGFUSE_PUBLIC_KEY") or _env("LANGFUSE_PUBLIC_KEY")
+    secret_key = _env("HERMES_LANGFUSE_SECRET_KEY") or _env("LANGFUSE_SECRET_KEY")
+    return bool(public_key and secret_key)
+
+
+def _get_langfuse() -> Optional[Langfuse]:
+    global _LANGFUSE_CLIENT
+    if not _is_enabled():
+        return None
+    if _LANGFUSE_CLIENT is not None:
+        return _LANGFUSE_CLIENT
+
+    public_key = _env("HERMES_LANGFUSE_PUBLIC_KEY") or _env("LANGFUSE_PUBLIC_KEY")
+    secret_key = _env("HERMES_LANGFUSE_SECRET_KEY") or _env("LANGFUSE_SECRET_KEY")
+    base_url = _env("HERMES_LANGFUSE_BASE_URL") or _env("LANGFUSE_BASE_URL") or "https://cloud.langfuse.com"
+    environment = _env("HERMES_LANGFUSE_ENV") or _env("LANGFUSE_ENV")
+    release = _env("HERMES_LANGFUSE_RELEASE") or _env("LANGFUSE_RELEASE")
+    sample_rate = _env("HERMES_LANGFUSE_SAMPLE_RATE")
+
+    kwargs: Dict[str, Any] = {
+        "public_key": public_key,
+        "secret_key": secret_key,
+        "base_url": base_url,
+    }
+    if environment:
+        kwargs["environment"] = environment
+    if release:
+        kwargs["release"] = release
+    if sample_rate:
+        try:
+            kwargs["sample_rate"] = float(sample_rate)
+        except ValueError:
+            logger.warning("Invalid HERMES_LANGFUSE_SAMPLE_RATE=%r", sample_rate)
+
+    try:
+        _LANGFUSE_CLIENT = Langfuse(**kwargs)
+    except Exception as exc:  # pragma: no cover - fail-open
+        logger.warning("Could not initialize Langfuse client: %s", exc)
+        return None
+
+    return _LANGFUSE_CLIENT
+
+
+def _trace_key(task_id: str, session_id: str) -> str:
+    if task_id:
+        return task_id
+    if session_id:
+        return f"session:{session_id}"
+    return f"thread:{threading.get_ident()}"
+
+
+def _truncate_text(value: str, max_chars: int) -> str:
+    if len(value) <= max_chars:
+        return value
+    return value[:max_chars] + f"... [truncated {len(value) - max_chars} chars]"
+
+
+def _maybe_parse_json_string(value: str) -> Any:
+    stripped = value.strip()
+    if len(stripped) < 2 or stripped[0] not in "{[" or stripped[-1] not in "}]":
+        if len(stripped) < 2 or stripped[0] not in "{[":
+            return value
+    try:
+        parsed, idx = json.JSONDecoder().raw_decode(stripped)
+    except Exception:
+        return value
+    if not isinstance(parsed, (dict, list)):
+        return value
+
+    trailing = stripped[idx:].strip()
+    if not trailing:
+        return parsed
+
+    hint_key = "_hint" if trailing.startswith("[Hint:") else "_trailing_text"
+    if isinstance(parsed, dict):
+        merged = dict(parsed)
+        key = hint_key if hint_key not in merged else "_trailing_text"
+        merged[key] = trailing
+        return merged
+
+    return {"data": parsed, hint_key: trailing}
+
+
+def _looks_like_read_file_payload(value: Any) -> bool:
+    if not isinstance(value, dict):
+        return False
+    content = value.get("content")
+    return (
+        isinstance(content, str)
+        and "total_lines" in value
+        and "file_size" in value
+        and "is_binary" in value
+        and "is_image" in value
+        and not value.get("error")
+    )
+
+
+def _parse_read_file_lines(content: str) -> list[dict[str, Any]]:
+    if not isinstance(content, str) or not content:
+        return []
+
+    lines = []
+    for raw_line in content.splitlines():
+        match = _READ_FILE_LINE_RE.match(raw_line)
+        if not match:
+            return []
+        lines.append({
+            "line": int(match.group(1)),
+            "text": match.group(2),
+        })
+    return lines
+
+
+def _build_read_file_preview(lines: list[dict[str, Any]]) -> dict[str, Any]:
+    if len(lines) <= (_READ_FILE_HEAD_LINES + _READ_FILE_TAIL_LINES):
+        return {"lines": lines}
+
+    return {
+        "head": lines[:_READ_FILE_HEAD_LINES],
+        "tail": lines[-_READ_FILE_TAIL_LINES:],
+        "omitted_line_count": len(lines) - _READ_FILE_HEAD_LINES - _READ_FILE_TAIL_LINES,
+    }
+
+
+def _normalize_read_file_payload(value: dict[str, Any], *, args: Any = None) -> dict[str, Any]:
+    normalized: dict[str, Any] = {}
+    if isinstance(args, dict):
+        path = args.get("path")
+        offset = args.get("offset")
+        limit = args.get("limit")
+        if isinstance(path, str) and path:
+            normalized["path"] = path
+        if isinstance(offset, int):
+            normalized["offset"] = offset
+        if isinstance(limit, int):
+            normalized["limit"] = limit
+
+    lines = _parse_read_file_lines(value.get("content", ""))
+    if lines:
+        normalized["returned_lines"] = {
+            "start": lines[0]["line"],
+            "end": lines[-1]["line"],
+            "count": len(lines),
+        }
+        normalized["content_preview"] = _build_read_file_preview(lines)
+    elif value.get("content"):
+        normalized["content_preview"] = {
+            "text": value.get("content", ""),
+        }
+
+    for key in (
+        "total_lines",
+        "file_size",
+        "truncated",
+        "is_binary",
+        "is_image",
+        "hint",
+        "_warning",
+        "mime_type",
+        "dimensions",
+        "similar_files",
+        "error",
+    ):
+        if key in value:
+            normalized[key] = value[key]
+
+    base64_content = value.get("base64_content")
+    if isinstance(base64_content, str) and base64_content:
+        normalized["base64_content"] = {
+            "omitted": True,
+            "length": len(base64_content),
+        }
+
+    return normalized
+
+
+def _normalize_payload(value: Any, *, tool_name: str = "", args: Any = None) -> Any:
+    if _looks_like_read_file_payload(value):
+        return _normalize_read_file_payload(
+            value,
+            args=args if tool_name == "read_file" else None,
+        )
+    return value
+
+
+def _safe_value(value: Any, *, max_chars: Optional[int] = None, depth: int = 0,
+                parse_json_strings: bool = False) -> Any:
+    max_chars = max_chars if max_chars is not None else int(_env("HERMES_LANGFUSE_MAX_CHARS", "12000") or "12000")
+    if depth > 4:
+        return "<max-depth>"
+    if value is None or isinstance(value, (int, float, bool)):
+        return value
+    if isinstance(value, bytes):
+        return {"type": "bytes", "len": len(value)}
+    if isinstance(value, str):
+        if parse_json_strings:
+            parsed = _maybe_parse_json_string(value)
+            if parsed is not value:
+                return _safe_value(parsed, max_chars=max_chars, depth=depth, parse_json_strings=True)
+        return _truncate_text(value, max_chars)
+    if isinstance(value, dict):
+        normalized = _normalize_payload(value)
+        if normalized is not value:
+            return _safe_value(normalized, max_chars=max_chars, depth=depth, parse_json_strings=parse_json_strings)
+        return {
+            str(k): _safe_value(v, max_chars=max_chars, depth=depth + 1, parse_json_strings=parse_json_strings)
+            for k, v in list(value.items())[:50]
+        }
+    if isinstance(value, (list, tuple, set)):
+        return [
+            _safe_value(v, max_chars=max_chars, depth=depth + 1, parse_json_strings=parse_json_strings)
+            for v in list(value)[:50]
+        ]
+    if hasattr(value, "__dict__"):
+        return _safe_value(vars(value), max_chars=max_chars, depth=depth + 1, parse_json_strings=parse_json_strings)
+    return _truncate_text(repr(value), max_chars)
+
+
+def _extract_last_user_message(messages: Any) -> Any:
+    if not isinstance(messages, list):
+        return None
+    for message in reversed(messages):
+        if isinstance(message, dict) and message.get("role") == "user":
+            return {
+                "role": "user",
+                "content": _safe_value(message.get("content")),
+            }
+    return None
+
+
+def _serialize_messages(messages: Any) -> list[dict[str, Any]]:
+    if not isinstance(messages, list):
+        return []
+    serialized = []
+    for message in messages[-12:]:
+        if not isinstance(message, dict):
+            continue
+        role = message.get("role")
+        item = {
+            "role": role,
+            "content": _safe_value(
+                message.get("content"),
+                parse_json_strings=(role == "tool"),
+            ),
+        }
+        if role == "tool" and message.get("tool_call_id"):
+            item["tool_call_id"] = message.get("tool_call_id")
+        if message.get("tool_calls"):
+            item["tool_calls"] = _safe_value(message.get("tool_calls"), parse_json_strings=True)
+        serialized.append(item)
+    return serialized
+
+
+def _serialize_tool_calls(tool_calls: Any) -> list[dict[str, Any]]:
+    if not tool_calls:
+        return []
+    serialized = []
+    for tool_call in tool_calls:
+        fn = getattr(tool_call, "function", None)
+        name = getattr(fn, "name", None) if fn else None
+        arguments = getattr(fn, "arguments", None) if fn else None
+        if isinstance(arguments, str):
+            try:
+                arguments = json.loads(arguments)
+            except Exception:
+                pass
+        serialized.append({
+            "id": getattr(tool_call, "id", None),
+            "name": name,
+            "arguments": _safe_value(arguments, parse_json_strings=True),
+        })
+    return serialized
+
+
+def _serialize_assistant_message(message: Any) -> dict[str, Any]:
+    return {
+        "content": _safe_value(getattr(message, "content", None)),
+        "reasoning": _safe_value(getattr(message, "reasoning", None)),
+        "tool_calls": _serialize_tool_calls(getattr(message, "tool_calls", None)),
+    }
+
+
+def _usage_and_cost(response: Any, *, provider: str, api_mode: str, model: str, base_url: str) -> tuple[dict[str, int], dict[str, float]]:
+    usage_details: Dict[str, int] = {}
+    cost_details: Dict[str, float] = {}
+    raw_usage = getattr(response, "usage", None)
+    if not raw_usage:
+        return usage_details, cost_details
+
+    try:
+        from agent.usage_pricing import estimate_usage_cost, normalize_usage
+
+        canonical = normalize_usage(raw_usage, provider=provider, api_mode=api_mode)
+        # Langfuse usage_details keys follow a naming convention:
+        #   - Dashboard sums all keys containing "input" as input total
+        #   - Dashboard sums all keys containing "output" as output total
+        #   - If no "total" key, Langfuse derives it from all usage types
+        # Use Anthropic-style key names so cache tokens roll into the
+        # dashboard input total automatically.
+        # Ref: https://langfuse.com/docs/model-usage-and-cost
+        usage_details = {
+            "input": canonical.input_tokens,
+            "output": canonical.output_tokens,
+        }
+        if canonical.cache_read_tokens:
+            usage_details["cache_read_input_tokens"] = canonical.cache_read_tokens
+        if canonical.cache_write_tokens:
+            usage_details["cache_creation_input_tokens"] = canonical.cache_write_tokens
+        if canonical.reasoning_tokens:
+            usage_details["reasoning_tokens"] = canonical.reasoning_tokens
+        cost = estimate_usage_cost(
+            model,
+            canonical,
+            provider=provider,
+            base_url=base_url,
+            api_key="",
+        )
+        if cost.amount_usd is not None:
+            # Langfuse cost_details keys must match usage_details keys.
+            # Provide per-type breakdown so dashboard can show cost by type.
+            try:
+                from agent.usage_pricing import get_pricing_entry
+                from decimal import Decimal
+                _ONE_M = Decimal("1000000")
+                entry = get_pricing_entry(model, provider=provider, base_url=base_url)
+                if entry:
+                    if entry.input_cost_per_million is not None and canonical.input_tokens:
+                        cost_details["input"] = float(Decimal(canonical.input_tokens) * entry.input_cost_per_million / _ONE_M)
+                    if entry.output_cost_per_million is not None and canonical.output_tokens:
+                        cost_details["output"] = float(Decimal(canonical.output_tokens) * entry.output_cost_per_million / _ONE_M)
+                    if entry.cache_read_cost_per_million is not None and canonical.cache_read_tokens:
+                        cost_details["cache_read_input_tokens"] = float(Decimal(canonical.cache_read_tokens) * entry.cache_read_cost_per_million / _ONE_M)
+                    if entry.cache_write_cost_per_million is not None and canonical.cache_write_tokens:
+                        cost_details["cache_creation_input_tokens"] = float(Decimal(canonical.cache_write_tokens) * entry.cache_write_cost_per_million / _ONE_M)
+                else:
+                    cost_details["total"] = float(cost.amount_usd)
+            except Exception:
+                cost_details["total"] = float(cost.amount_usd)
+    except Exception as exc:  # pragma: no cover - fail-open
+        _debug(f"usage normalization failed: {exc}")
+
+    return usage_details, cost_details
+
+
+def _start_root_trace(task_key: str, *, task_id: str, session_id: str, platform: str, provider: str, model: str,
+                      api_mode: str, messages: Any, client: Langfuse) -> TraceState:
+    trace_id = client.create_trace_id(seed=f"{session_id or 'sessionless'}::{task_id or task_key}")
+    trace_input = _extract_last_user_message(messages)
+    metadata = {
+        "source": "hermes",
+        "task_id": task_id,
+        "platform": platform,
+        "provider": provider,
+        "model": model,
+        "api_mode": api_mode,
+    }
+
+    # session_id must be passed in trace_context for Langfuse session grouping.
+    trace_ctx: Dict[str, Any] = {"trace_id": trace_id}
+    if session_id:
+        trace_ctx["session_id"] = session_id
+
+    if propagate_attributes is not None:
+        try:
+            with propagate_attributes(
+                session_id=session_id or task_key,
+                trace_name="Hermes turn",
+                tags=["hermes", "langfuse"],
+            ):
+                root_ctx = client.start_as_current_observation(
+                    trace_context=trace_ctx,
+                    name="Hermes turn",
+                    as_type="chain",
+                    input=trace_input,
+                    metadata=metadata,
+                    end_on_exit=False,
+                )
+                root_span = root_ctx.__enter__()
+        except Exception:
+            root_ctx = client.start_as_current_observation(
+                trace_context=trace_ctx,
+                name="Hermes turn",
+                as_type="chain",
+                input=trace_input,
+                metadata=metadata,
+                end_on_exit=False,
+            )
+            root_span = root_ctx.__enter__()
+    else:
+        root_ctx = client.start_as_current_observation(
+            trace_context=trace_ctx,
+            name="Hermes turn",
+            as_type="chain",
+            input=trace_input,
+            metadata=metadata,
+            end_on_exit=False,
+        )
+        root_span = root_ctx.__enter__()
+
+    try:
+        root_span.set_trace_io(input=trace_input)
+    except Exception:
+        pass
+
+    _debug(f"started trace {trace_id} for {task_key}")
+    return TraceState(trace_id=trace_id, root_ctx=root_ctx, root_span=root_span)
+
+
+def _start_child_observation(state: TraceState, *, client: Langfuse, name: str, as_type: str,
+                             input_value: Any, metadata: Optional[dict] = None,
+                             model: Optional[str] = None, model_parameters: Optional[dict] = None) -> Any:
+    return state.root_span.start_observation(
+        name=name,
+        as_type=as_type,
+        input=input_value,
+        metadata=metadata or {},
+        model=model,
+        model_parameters=model_parameters,
+    )
+
+
+def _end_observation(observation: Any, *, output: Any = None, metadata: Optional[dict] = None,
+                     usage_details: Optional[dict] = None, cost_details: Optional[dict] = None) -> None:
+    if observation is None:
+        return
+    try:
+        update_kwargs: Dict[str, Any] = {}
+        if output is not None:
+            update_kwargs["output"] = output
+        if metadata:
+            update_kwargs["metadata"] = metadata
+        if usage_details:
+            update_kwargs["usage_details"] = usage_details
+        if cost_details:
+            update_kwargs["cost_details"] = cost_details
+        if update_kwargs:
+            observation.update(**update_kwargs)
+        observation.end()
+    except Exception as exc:  # pragma: no cover - fail-open
+        _debug(f"end observation failed: {exc}")
+
+
+def _merge_trace_output(output: Any, state: TraceState) -> Any:
+    if not state.turn_tool_calls:
+        return output
+
+    merged = dict(output) if isinstance(output, dict) else {"content": output}
+    merged["tool_calls"] = list(state.turn_tool_calls)
+    return merged
+
+
+def _finish_trace(task_key: str, *, output: Any = None) -> None:
+    client = _get_langfuse()
+    if client is None:
+        return
+
+    with _STATE_LOCK:
+        state = _TRACE_STATE.pop(task_key, None)
+    if state is None:
+        return
+
+    try:
+        for observation in state.generations.values():
+            _end_observation(observation)
+        for observation in state.tools.values():
+            _end_observation(observation)
+        final_output = _merge_trace_output(output, state)
+        if final_output is not None:
+            state.root_span.set_trace_io(output=final_output)
+            state.root_span.update(output=final_output)
+        state.root_span.end()
+    except Exception as exc:  # pragma: no cover - fail-open
+        _debug(f"finish trace failed: {exc}")
+    finally:
+        try:
+            client.flush()
+        except Exception:
+            pass
+
+
+def _assistant_has_tool_calls(message: Any) -> bool:
+    return bool(getattr(message, "tool_calls", None))
+
+
+def _request_key(api_call_count: Any) -> str:
+    return str(api_call_count or 0)
+
+
+def on_pre_llm_call(*, task_id: str = "", session_id: str = "", platform: str = "", model: str = "",
+                    provider: str = "", base_url: str = "", api_mode: str = "",
+                    api_call_count: int = 0, messages: Any = None, turn_type: str = "user",
+                    conversation_history: Any = None, user_message: Any = None, **_: Any) -> None:
+    # Older Hermes branches used pre_llm_call for request-scoped tracing and
+    # passed the actual API messages. Current Hermes also has a turn-scoped
+    # pre_llm_call used for context injection; tracing that hook creates an
+    # extra orphan/root trace before the real request trace. Only trace the
+    # legacy request-shaped call here.
+    if not isinstance(messages, list):
+        return
+
+    client = _get_langfuse()
+    if client is None:
+        return
+
+    # messages is a list only for legacy Hermes branches that fired
+    # pre_llm_call with API messages directly. Current Hermes fires
+    # pre_llm_call for context injection (conversation_history/user_message,
+    # no messages list) — tracing that would create orphan traces.
+    task_key = _trace_key(task_id, session_id)
+
+    with _STATE_LOCK:
+        state = _TRACE_STATE.get(task_key)
+        if state is None:
+            state = _start_root_trace(
+                task_key,
+                task_id=task_id,
+                session_id=session_id,
+                platform=platform,
+                provider=provider,
+                model=model,
+                api_mode=api_mode,
+                messages=messages,
+                client=client,
+            )
+            _TRACE_STATE[task_key] = state
+        state.last_updated_at = time.time()
+
+
+def on_pre_llm_request(
+    *,
+    task_id: str = "",
+    session_id: str = "",
+    platform: str = "",
+    model: str = "",
+    provider: str = "",
+    base_url: str = "",
+    api_mode: str = "",
+    api_call_count: int = 0,
+    messages: Any = None,
+    turn_type: str = "user",
+    message_count: int = 0,
+    tool_count: int = 0,
+    approx_input_tokens: int = 0,
+    request_char_count: int = 0,
+    max_tokens: Any = None,
+    **_: Any,
+) -> None:
+    client = _get_langfuse()
+    if client is None:
+        return
+
+    task_key = _trace_key(task_id, session_id)
+    req_key = _request_key(api_call_count)
+
+    with _STATE_LOCK:
+        state = _TRACE_STATE.get(task_key)
+        if state is None:
+            state = _start_root_trace(
+                task_key,
+                task_id=task_id,
+                session_id=session_id,
+                platform=platform,
+                provider=provider,
+                model=model,
+                api_mode=api_mode,
+                messages=messages,
+                client=client,
+            )
+            _TRACE_STATE[task_key] = state
+        state.last_updated_at = time.time()
+        previous = state.generations.pop(req_key, None)
+        if previous is not None:
+            _end_observation(previous)
+        state.generations[req_key] = _start_child_observation(
+            state,
+            client=client,
+            name=f"LLM call {api_call_count}",
+            as_type="generation",
+            input_value=_serialize_messages(messages),
+            metadata={
+                "provider": provider,
+                "platform": platform,
+                "api_mode": api_mode,
+                "base_url": base_url,
+            },
+            model=model,
+            model_parameters={"api_mode": api_mode, "provider": provider},
+        )
+
+
+def on_post_llm_call(*, task_id: str = "", session_id: str = "", provider: str = "", base_url: str = "",
+                     api_mode: str = "", model: str = "", api_call_count: int = 0,
+                     assistant_message: Any = None, response: Any = None,
+                     api_duration: float = 0.0, finish_reason: str = "",
+                     usage: Any = None, assistant_content_chars: int = 0,
+                     assistant_tool_call_count: int = 0, assistant_response: Any = None,
+                     **_: Any) -> None:
+    client = _get_langfuse()
+    if client is None:
+        return
+
+    task_key = _trace_key(task_id, session_id)
+    req_key = _request_key(api_call_count)
+
+    with _STATE_LOCK:
+        state = _TRACE_STATE.get(task_key)
+        generation = state.generations.pop(req_key, None) if state else None
+    if state is None or generation is None:
+        return
+
+    # Handle both call patterns:
+    # 1. post_api_request: passes usage (dict), assistant_content_chars, assistant_tool_call_count
+    # 2. post_llm_call: passes assistant_message (object), response (object), assistant_response (str)
+    if assistant_message is not None:
+        output = _serialize_assistant_message(assistant_message)
+    elif assistant_response is not None:
+        # post_llm_call passes assistant_response as a plain string
+        output = {"content": _safe_value(assistant_response), "reasoning": None, "tool_calls": []}
+    else:
+        # post_api_request path — reconstruct from summary kwargs
+        output = {
+            "content": f"[{assistant_content_chars} chars]" if assistant_content_chars else None,
+            "reasoning": None,
+            "tool_calls": [{"id": f"tc_{i}"} for i in range(assistant_tool_call_count)] if assistant_tool_call_count else [],
+        }
+
+    if output.get("tool_calls"):
+        state.turn_tool_calls.extend(output["tool_calls"])
+
+    # Extract usage: prefer response object, fall back to usage dict from post_api_request
+    if response is not None:
+        usage_details, cost_details = _usage_and_cost(
+            response,
+            provider=provider,
+            api_mode=api_mode,
+            model=model,
+            base_url=base_url,
+        )
+    elif isinstance(usage, dict) and usage:
+        # post_api_request passes a pre-built CanonicalUsage summary dict.
+        # Use Langfuse-convention key names: "input", "output", and
+        # "cache_read_input_tokens" / "cache_creation_input_tokens" so the
+        # dashboard sums cache tokens into the input total automatically.
+        _input = usage.get("input_tokens", 0)
+        _output = usage.get("output_tokens", 0) or usage.get("completion_tokens", 0)
+        _cache_read = usage.get("cache_read_tokens", 0)
+        _cache_write = usage.get("cache_write_tokens", 0)
+        _reasoning = usage.get("reasoning_tokens", 0)
+        usage_details = {
+            "input": _input,
+            "output": _output,
+        }
+        if _cache_read:
+            usage_details["cache_read_input_tokens"] = _cache_read
+        if _cache_write:
+            usage_details["cache_creation_input_tokens"] = _cache_write
+        if _reasoning:
+            usage_details["reasoning_tokens"] = _reasoning
+        cost_details = {}
+        # Estimate per-type cost from the summary if possible
+        try:
+            from agent.usage_pricing import CanonicalUsage, estimate_usage_cost, get_pricing_entry
+            from decimal import Decimal
+            _ONE_M = Decimal("1000000")
+            _cu = CanonicalUsage(
+                input_tokens=_input,
+                output_tokens=_output,
+                cache_read_tokens=_cache_read,
+                cache_write_tokens=_cache_write,
+                reasoning_tokens=_reasoning,
+            )
+            entry = get_pricing_entry(model, provider=provider, base_url=base_url)
+            if entry:
+                if entry.input_cost_per_million is not None and _input:
+                    cost_details["input"] = float(Decimal(_input) * entry.input_cost_per_million / _ONE_M)
+                if entry.output_cost_per_million is not None and _output:
+                    cost_details["output"] = float(Decimal(_output) * entry.output_cost_per_million / _ONE_M)
+                if entry.cache_read_cost_per_million is not None and _cache_read:
+                    cost_details["cache_read_input_tokens"] = float(Decimal(_cache_read) * entry.cache_read_cost_per_million / _ONE_M)
+                if entry.cache_write_cost_per_million is not None and _cache_write:
+                    cost_details["cache_creation_input_tokens"] = float(Decimal(_cache_write) * entry.cache_write_cost_per_million / _ONE_M)
+            else:
+                _cost = estimate_usage_cost(model, _cu, provider=provider, base_url=base_url, api_key="")
+                if _cost.amount_usd is not None:
+                    cost_details["total"] = float(_cost.amount_usd)
+        except Exception:
+            pass
+    else:
+        usage_details, cost_details = {}, {}
+
+    tool_count = len(output.get("tool_calls", [])) or assistant_tool_call_count
+    gen_metadata: Dict[str, Any] = {"tool_call_count": tool_count}
+    if api_duration and api_duration > 0:
+        gen_metadata["api_duration_s"] = round(api_duration, 3)
+    if finish_reason:
+        gen_metadata["finish_reason"] = finish_reason
+    _end_observation(
+        generation,
+        output=output,
+        usage_details=usage_details,
+        cost_details=cost_details,
+        metadata=gen_metadata,
+    )
+
+    has_tools = _assistant_has_tool_calls(assistant_message) if assistant_message else (assistant_tool_call_count > 0)
+    has_content = bool(output.get("content"))
+    if not has_tools and has_content:
+        _finish_trace(task_key, output=output)
+
+
+def on_pre_tool_call(*, tool_name: str = "", args: Any = None, task_id: str = "",
+                     session_id: str = "", tool_call_id: str = "", **_: Any) -> None:
+    client = _get_langfuse()
+    if client is None:
+        return
+
+    task_key = _trace_key(task_id, session_id)
+    tool_key = tool_call_id or f"{tool_name}:{time.time_ns()}"
+
+    with _STATE_LOCK:
+        state = _TRACE_STATE.get(task_key)
+        if state is None:
+            return
+        state.tools[tool_key] = _start_child_observation(
+            state,
+            client=client,
+            name=f"Tool: {tool_name}",
+            as_type="tool",
+            input_value=_safe_value(args),
+            metadata={"tool_name": tool_name, "tool_call_id": tool_call_id},
+        )
+
+
+def on_post_tool_call(*, tool_name: str = "", args: Any = None, result: Any = None,
+                      task_id: str = "", session_id: str = "", tool_call_id: str = "", **_: Any) -> None:
+    task_key = _trace_key(task_id, session_id)
+    tool_key = tool_call_id or ""
+    observation = None
+
+    with _STATE_LOCK:
+        state = _TRACE_STATE.get(task_key)
+        if state is None:
+            return
+        if tool_key:
+            observation = state.tools.pop(tool_key, None)
+        elif state.tools:
+            _, observation = state.tools.popitem()
+
+    if observation is None:
+        return
+
+    if isinstance(result, str):
+        result_value = _maybe_parse_json_string(result)
+    else:
+        result_value = result
+    result_value = _normalize_payload(result_value, tool_name=tool_name, args=args)
+
+    _end_observation(
+        observation,
+        output=_safe_value(result_value, parse_json_strings=True),
+        metadata={"tool_name": tool_name, "args": _safe_value(args, parse_json_strings=True)},
+    )
+
+
+def register(ctx) -> None:
+    # Register for both hook name variants so the plugin works across
+    # Hermes versions.  pre_api_request / post_api_request fire per API
+    # call (preferred); pre_llm_call / post_llm_call fire once per turn.
+    ctx.register_hook("pre_api_request", on_pre_llm_request)
+    ctx.register_hook("post_api_request", on_post_llm_call)
+    ctx.register_hook("pre_llm_call", on_pre_llm_call)
+    ctx.register_hook("post_llm_call", on_post_llm_call)
+    ctx.register_hook("pre_tool_call", on_pre_tool_call)
+    ctx.register_hook("post_tool_call", on_post_tool_call)

optional-plugins/observability/langfuse/after-install.md

@@ -0,0 +1,38 @@
+# After installing langfuse
+
+Langfuse tracing is now installed and enabled for your Hermes profile.
+
+## Required credentials
+
+Set these in `~/.hermes/.env` (or via `hermes tools` → Langfuse Observability):
+
+```bash
+HERMES_LANGFUSE_PUBLIC_KEY=pk-lf-...
+HERMES_LANGFUSE_SECRET_KEY=sk-lf-...
+HERMES_LANGFUSE_BASE_URL=https://cloud.langfuse.com   # or your self-hosted URL
+```
+
+## Verify
+
+```bash
+hermes plugins list          # langfuse should appear as enabled
+hermes chat -q "hello"       # then check Langfuse for a "Hermes turn" trace
+```
+
+## Optional settings
+
+```bash
+HERMES_LANGFUSE_ENV=production       # environment tag
+HERMES_LANGFUSE_RELEASE=v1.0.0      # release tag
+HERMES_LANGFUSE_SAMPLE_RATE=0.5     # sample 50% of traces
+HERMES_LANGFUSE_MAX_CHARS=12000     # max chars per field (default: 12000)
+HERMES_LANGFUSE_DEBUG=true          # verbose plugin logging
+```
+
+## Dependencies
+
+The `langfuse` Python SDK is required. Install it into your Hermes venv:
+
+```bash
+pip install langfuse
+```

optional-plugins/observability/langfuse/plugin.yaml

@@ -0,0 +1,14 @@
+name: langfuse
+version: "1.0.0"
+description: "Optional Langfuse observability for Hermes — traces conversations, LLM calls, and tool usage. Install via: hermes plugins install official/observability/langfuse"
+author: NousResearch
+requires_env:
+  - HERMES_LANGFUSE_PUBLIC_KEY
+  - HERMES_LANGFUSE_SECRET_KEY
+hooks:
+  - pre_api_request
+  - post_api_request
+  - pre_llm_call
+  - post_llm_call
+  - pre_tool_call
+  - post_tool_call

tests/hermes_cli/test_optional_plugins.py

@@ -0,0 +1,168 @@
+"""Tests for optional-plugins (official) install path in plugins_cmd."""
+from __future__ import annotations
+
+from pathlib import Path
+from unittest.mock import MagicMock, patch
+
+import pytest
+
+
+# ---------------------------------------------------------------------------
+# Helpers
+# ---------------------------------------------------------------------------
+
+def _make_official_plugin_dir(tmp_path: Path, category: str, name: str) -> Path:
+    """Create a minimal optional-plugin directory structure."""
+    plugin_dir = tmp_path / "optional-plugins" / category / name
+    plugin_dir.mkdir(parents=True)
+    (plugin_dir / "plugin.yaml").write_text(
+        f"name: {name}\nversion: 1.0.0\ndescription: Test plugin\n"
+    )
+    (plugin_dir / "__init__.py").write_text("def register(ctx): pass\n")
+    return plugin_dir
+
+
+# ---------------------------------------------------------------------------
+# _resolve_official_plugin
+# ---------------------------------------------------------------------------
+
+class TestResolveOfficialPlugin:
+    def test_returns_none_for_git_url(self, tmp_path):
+        from hermes_cli.plugins_cmd import _resolve_official_plugin
+        with patch("hermes_cli.plugins_cmd._optional_plugins_dir", return_value=tmp_path / "optional-plugins"):
+            result = _resolve_official_plugin("https://github.com/owner/repo.git")
+        assert result is None
+
+    def test_returns_none_for_owner_repo(self, tmp_path):
+        from hermes_cli.plugins_cmd import _resolve_official_plugin
+        with patch("hermes_cli.plugins_cmd._optional_plugins_dir", return_value=tmp_path / "optional-plugins"):
+            result = _resolve_official_plugin("owner/repo")
+        assert result is None
+
+    def test_returns_none_for_missing_plugin(self, tmp_path):
+        from hermes_cli.plugins_cmd import _resolve_official_plugin
+        (tmp_path / "optional-plugins").mkdir()
+        with patch("hermes_cli.plugins_cmd._optional_plugins_dir", return_value=tmp_path / "optional-plugins"):
+            result = _resolve_official_plugin("official/observability/nonexistent")
+        assert result is None
+
+    def test_returns_path_for_existing_plugin(self, tmp_path):
+        from hermes_cli.plugins_cmd import _resolve_official_plugin
+        plugin_dir = _make_official_plugin_dir(tmp_path, "observability", "langfuse")
+        with patch("hermes_cli.plugins_cmd._optional_plugins_dir", return_value=tmp_path / "optional-plugins"):
+            result = _resolve_official_plugin("official/observability/langfuse")
+        assert result == plugin_dir
+
+    def test_accepts_without_official_prefix(self, tmp_path):
+        from hermes_cli.plugins_cmd import _resolve_official_plugin
+        plugin_dir = _make_official_plugin_dir(tmp_path, "observability", "langfuse")
+        with patch("hermes_cli.plugins_cmd._optional_plugins_dir", return_value=tmp_path / "optional-plugins"):
+            result = _resolve_official_plugin("observability/langfuse")
+        assert result == plugin_dir
+
+    def test_traversal_blocked(self, tmp_path):
+        from hermes_cli.plugins_cmd import _resolve_official_plugin
+        (tmp_path / "optional-plugins").mkdir()
+        with patch("hermes_cli.plugins_cmd._optional_plugins_dir", return_value=tmp_path / "optional-plugins"):
+            result = _resolve_official_plugin("official/../../etc/passwd")
+        assert result is None
+
+
+# ---------------------------------------------------------------------------
+# _list_official_plugins
+# ---------------------------------------------------------------------------
+
+class TestListOfficialPlugins:
+    def test_empty_when_no_optional_plugins_dir(self, tmp_path):
+        from hermes_cli.plugins_cmd import _list_official_plugins
+        with patch("hermes_cli.plugins_cmd._optional_plugins_dir", return_value=tmp_path / "nonexistent"):
+            result = _list_official_plugins()
+        assert result == []
+
+    def test_lists_plugins_with_descriptions(self, tmp_path):
+        from hermes_cli.plugins_cmd import _list_official_plugins
+        _make_official_plugin_dir(tmp_path, "observability", "langfuse")
+        _make_official_plugin_dir(tmp_path, "observability", "other-plugin")
+        with patch("hermes_cli.plugins_cmd._optional_plugins_dir", return_value=tmp_path / "optional-plugins"):
+            result = _list_official_plugins()
+        identifiers = [r[0] for r in result]
+        assert "official/observability/langfuse" in identifiers
+        assert "official/observability/other-plugin" in identifiers
+
+    def test_descriptions_parsed_from_yaml(self, tmp_path):
+        from hermes_cli.plugins_cmd import _list_official_plugins
+        plugin_dir = _make_official_plugin_dir(tmp_path, "observability", "langfuse")
+        with patch("hermes_cli.plugins_cmd._optional_plugins_dir", return_value=tmp_path / "optional-plugins"):
+            result = _list_official_plugins()
+        assert any(desc == "Test plugin" for _, desc in result)
+
+
+# ---------------------------------------------------------------------------
+# cmd_install — official path
+# ---------------------------------------------------------------------------
+
+class TestCmdInstallOfficial:
+    def test_install_official_plugin_copies_files(self, tmp_path, monkeypatch):
+        from hermes_cli.plugins_cmd import cmd_install
+        plugin_dir = _make_official_plugin_dir(tmp_path, "observability", "langfuse")
+        user_plugins = tmp_path / "user-plugins"
+        user_plugins.mkdir()
+
+        monkeypatch.setattr("hermes_cli.plugins_cmd._optional_plugins_dir",
+                            lambda: tmp_path / "optional-plugins")
+        monkeypatch.setattr("hermes_cli.plugins_cmd._plugins_dir",
+                            lambda: user_plugins)
+        # Non-interactive: don't prompt
+        monkeypatch.setattr("sys.stdin.isatty", lambda: False)
+
+        cmd_install("official/observability/langfuse", enable=False)
+
+        installed = user_plugins / "langfuse"
+        assert installed.is_dir()
+        assert (installed / "plugin.yaml").exists()
+        assert (installed / "__init__.py").exists()
+
+    def test_install_official_plugin_respects_force(self, tmp_path, monkeypatch):
+        from hermes_cli.plugins_cmd import cmd_install
+        plugin_dir = _make_official_plugin_dir(tmp_path, "observability", "langfuse")
+        user_plugins = tmp_path / "user-plugins"
+        user_plugins.mkdir()
+        # Pre-create to simulate already-installed
+        already = user_plugins / "langfuse"
+        already.mkdir()
+        (already / "old.txt").write_text("old")
+
+        monkeypatch.setattr("hermes_cli.plugins_cmd._optional_plugins_dir",
+                            lambda: tmp_path / "optional-plugins")
+        monkeypatch.setattr("hermes_cli.plugins_cmd._plugins_dir",
+                            lambda: user_plugins)
+        monkeypatch.setattr("sys.stdin.isatty", lambda: False)
+
+        cmd_install("official/observability/langfuse", force=True, enable=False)
+
+        # Old file should be gone, new files present
+        assert not (already / "old.txt").exists()
+        assert (already / "plugin.yaml").exists()
+
+    def test_install_official_plugin_exits_without_force_when_exists(self, tmp_path, monkeypatch):
+        from hermes_cli.plugins_cmd import cmd_install
+        _make_official_plugin_dir(tmp_path, "observability", "langfuse")
+        user_plugins = tmp_path / "user-plugins"
+        user_plugins.mkdir()
+        (user_plugins / "langfuse").mkdir()
+
+        monkeypatch.setattr("hermes_cli.plugins_cmd._optional_plugins_dir",
+                            lambda: tmp_path / "optional-plugins")
+        monkeypatch.setattr("hermes_cli.plugins_cmd._plugins_dir",
+                            lambda: user_plugins)
+
+        with pytest.raises(SystemExit):
+            cmd_install("official/observability/langfuse", enable=False)
+
+    def test_git_url_not_mistaken_for_official(self, tmp_path, monkeypatch):
+        """A git URL must not trigger the official install path."""
+        from hermes_cli.plugins_cmd import _resolve_official_plugin
+        with patch("hermes_cli.plugins_cmd._optional_plugins_dir",
+                   return_value=tmp_path / "optional-plugins"):
+            assert _resolve_official_plugin("https://github.com/owner/repo") is None
+            assert _resolve_official_plugin("owner/repo") is None