Claude-Code-Monitor/docs/HOOKS.md

Hook System Integration Guide

Comprehensive guide to integrating with Claude Code's hook system for real-time agent monitoring.

---

Table of Contents

• Overview
• Hook Architecture
• Hook Installation
• Hook Types
• Hook Handler Implementation
• Event Processing
• Error Handling
• Performance Considerations
• Testing Hooks
• Troubleshooting

---

Overview

Claude Code provides a hook system that allows external tools to receive real-time events during agent execution. Agent Dashboard uses these hooks to capture session lifecycle, tool executions, and notifications.

Cursor (informational): Live hooks fire from Claude Code. Cursor sessions that only exist as JSONL under ~/.claude (Cursor uses the same paths locally) are still counted — they appear via startup import, continuous project sync, or remote SSH sync, not via hooks.

graph TB
    subgraph "Claude Code Process"
        CLI[Claude CLI]
        Agent[Agent Execution]
        Hooks[Hook System]
    end
    
    subgraph "Hook Wiring (~/.claude/settings.json)"
        SessionStart[SessionStart]
        UserPromptSubmit[UserPromptSubmit]
        PreTool[PreToolUse]
        PostTool[PostToolUse]
        Stop[Stop]
        SubagentStop[SubagentStop]
        Notification[Notification]
        SessionEnd[SessionEnd]
    end

    subgraph "Hook Handler"
        Handler[hook-handler.js]
    end

    subgraph "Dashboard Server"
        API[Express Server<br/>:4820]
    end

    Agent --> Hooks
    Hooks -->|stdin JSON| SessionStart
    Hooks -->|stdin JSON| UserPromptSubmit
    Hooks -->|stdin JSON| PreTool
    Hooks -->|stdin JSON| PostTool
    Hooks -->|stdin JSON| Stop
    Hooks -->|stdin JSON| SubagentStop
    Hooks -->|stdin JSON| Notification
    Hooks -->|stdin JSON| SessionEnd

    SessionStart -->|exec| Handler
    UserPromptSubmit -->|exec| Handler
    PreTool -->|exec| Handler
    PostTool -->|exec| Handler
    Stop -->|exec| Handler
    SubagentStop -->|exec| Handler
    Notification -->|exec| Handler
    SessionEnd -->|exec| Handler
    
    Handler -->|HTTP POST| API
    
    style Hooks fill:#F59E0B
    style Handler fill:#10B981
    style API fill:#3B82F6

---

Hook Architecture

Hook Execution Flow

sequenceDiagram
    participant Claude as Claude Code
    participant HookScript as Hook Script<br/>(Python)
    participant Handler as hook-handler.js
    participant Server as Dashboard Server
    participant DB as SQLite
    participant WS as WebSocket
    
    Claude->>HookScript: Execute (stdin: JSON)
    HookScript->>HookScript: Read stdin
    HookScript->>Handler: exec node hook-handler.js
    Handler->>Handler: Parse JSON
    Handler->>Server: HTTP POST /hooks/{type}
    Server->>DB: Insert/Update data
    DB-->>Server: Success
    Server->>WS: Broadcast event
    WS-->>Server: Sent to clients
    Server-->>Handler: 200 OK
    Handler-->>HookScript: exit 0
    HookScript-->>Claude: exit 0 (non-blocking)
    
    Note over Claude: Continues execution<br/>without waiting

Security: the hook handler POSTs to the loopback dashboard (127.0.0.1:<port>). The /api/hooks ingestion path is exempt from the optional DASHBOARD_TOKEN gate — it is a local-only write — so hooks keep working without a token even when one is configured for the rest of the API (GHSA-gr74-4xfh-6jw9).

Hook System Characteristics

Design Principles:

graph TB
    subgraph "Hook System Goals"
        NonBlocking[Non-Blocking<br/>Never block Claude Code]
        FailSafe[Fail-Safe<br/>Errors don't stop execution]
        FastExec[Fast Execution<br/>&lt; 100ms per hook]
        Complete[Complete Data<br/>Capture all events]
    end
    
    subgraph "Implementation"
        Timeout[5s Timeout]
        ErrorLog[Silent Error Logging]
        Async[Async HTTP POST]
        JSON[JSON Serialization]
    end
    
    NonBlocking --> Timeout
    FailSafe --> ErrorLog
    FastExec --> Async
    Complete --> JSON
    
    style NonBlocking fill:#10B981
    style FailSafe fill:#10B981
    style FastExec fill:#10B981

---

Hook Installation

Installation Script

# Install hooks
npm run install-hooks

Important

Skip this entirely when the ccam plugin is installed. The plugin declares the same eight hooks itself (inline in .claude-plugin/plugin.json, each running ${CLAUDE_PLUGIN_ROOT}/scripts/hook-handler.js). Running both means every event is POSTed twice — events carry no id, so ingest cannot deduplicate them and every token and cost figure doubles. scripts/plugin-bootstrap.js removes checkout-installed entries on session start (backup: ~/.claude/settings.json.ccam-bak), install-hooks.js warns when it detects a plugin install, and /ccam-doctor reports any duplicates that remain. See PLUGINS.md.

Important

Hooks are a host-side step. Claude Code runs on your host, so the hook command must reference a hook-handler.js path that exists on the host. Run npm run install-hooks on the host — never inside a container. When run inside Docker/Podman, the installer refuses and exits non-zero (issue #193): a container-internal path written into a bind-mounted ~/.claude would break every host hook with MODULE_NOT_FOUND. The host handler POSTs to http://localhost:4820, which a containerized dashboard already publishes. (Escape hatch for running Claude Code inside the same container: CCAM_ALLOW_CONTAINER_HOOKS=1 npm run install-hooks.)

This copies hook scripts from scripts/hooks/ to .githooks/:

graph LR
    Source[scripts/hooks/*.py] -->|Copy| Target[.githooks/*.py]
    Handler[scripts/hook-handler.js] -->|Reference| Target
    
    Target -->|chmod +x| Executable[Executable Hooks]
    
    style Source fill:#3B82F6
    style Executable fill:#10B981

Manual Installation

#!/bin/bash
# scripts/install-hooks.js

HOOKS_DIR=".githooks"
SOURCE_DIR="scripts/hooks"

# Create hooks directory
mkdir -p "$HOOKS_DIR"

# Copy hook scripts
cp "$SOURCE_DIR/session-start.py" "$HOOKS_DIR/"
cp "$SOURCE_DIR/pre-tool-use.py" "$HOOKS_DIR/"
cp "$SOURCE_DIR/post-tool-use.py" "$HOOKS_DIR/"
cp "$SOURCE_DIR/stop.py" "$HOOKS_DIR/"
cp "$SOURCE_DIR/subagent-stop.py" "$HOOKS_DIR/"
cp "$SOURCE_DIR/notification.py" "$HOOKS_DIR/"
cp "$SOURCE_DIR/session-end.py" "$HOOKS_DIR/"

# Make executable
chmod +x "$HOOKS_DIR"/*.py

echo "Hooks installed in .githooks/"

Verification

# Check hook files exist
ls -la .githooks/

# Expected output:
# session-start.py
# pre-tool-use.py
# post-tool-use.py
# stop.py
# subagent-stop.py
# notification.py
# session-end.py

---

Hook Types

1. SessionStart

Triggered when a Claude Code session starts. The source field distinguishes the trigger: startup (fresh launch), resume (--resume/--continue), clear (/clear), and compact — which fires mid-turn when auto-compaction kicks in while Claude is actively working, not at a fresh prompt.

Payload Example:

{
  "type": "sessionStart",
  "sessionId": "sess_abc123",
  "source": "startup",
  "model": "claude-sonnet-4",
  "timestamp": "2024-03-18T12:00:00Z"
}

Purpose:

• Create the session and main-agent records on first contact
• Stamp awaiting_input_since (with awaiting_reason = session_start) so the dashboard shows the row in Waiting from the moment the CLI lands at a prompt — only for startup/resume/clear. A compact-source SessionStart fires mid-turn while Claude is working, so it leaves the awaiting flag untouched: a genuinely-active session stays Active (not flipped to Waiting), and a session that compacted while idle keeps its existing Waiting flag and reason
• Reactivate completed/abandoned sessions on resume
• Sweep other active sessions whose last activity is older than DASHBOARD_STALE_MINUTES (default 180), marking them abandoned with their agents completed (Remote Data Source sessions, source ≠ local, are exempt — their status comes from the SSH-mirror reconciliation, not local activity)

---

2. UserPromptSubmit

Triggered the moment the user hits enter on a prompt — fires before Claude does any work.

Payload Example:

{
  "type": "userPromptSubmit",
  "sessionId": "sess_abc123",
  "prompt": "Refactor this function...",
  "timestamp": "2024-03-18T12:00:30Z"
}

Purpose:

• Clear awaiting_input_since (and awaiting_reason — both reset to NULL together) on the session and main agent
• Promote the main agent to working so the dashboard reflects "Claude is now thinking on this" through the entire response — including text-only replies that emit no PreToolUse before Stop

---

3. PreToolUse

Triggered before a tool executes.

Payload Example:

{
  "type": "preToolUse",
  "sessionId": "sess_abc123",
  "agentId": "agent_main_001",
  "toolName": "bash",
  "timestamp": "2024-03-18T12:01:00Z"
}

Purpose:

• Clear awaiting_input_since (and awaiting_reason — both reset to NULL together; Claude can only call a tool after fresh user input)
• Set agent to working, set current_tool
• Track tool execution start time
• If tool name is Agent, create a subagent record

---

4. PostToolUse

Triggered after a tool completes execution.

Payload Example:

{
  "type": "postToolUse",
  "sessionId": "sess_abc123",
  "agentId": "agent_main_001",
  "toolName": "bash",
  "durationMs": 1234,
  "success": true,
  "inputTokens": 1500,
  "outputTokens": 800,
  "timestamp": "2024-03-18T12:01:01.234Z"
}

Purpose:

• Clear awaiting_input_since (and awaiting_reason — both reset to NULL together; covers permission-prompt approval mid-tool)
• Clear current_tool on agent (agent stays working)
• Update agent token counts via shared transcript cache
• Calculate and update cost
• Rollup cost to session

Cost Calculation Flow:

graph TB
    PostHook[PostToolUse Hook] --> Tokens{Has Token<br/>Counts?}
    Tokens -->|Yes| Pricing[Fetch Pricing Rule]
    Tokens -->|No| Skip[Skip Cost Update]
    
    Pricing --> Calculate[Cost = <br/>input/1M * input_price +<br/>output/1M * output_price]
    Calculate --> UpdateAgent[Update agent.cost]
    UpdateAgent --> Rollup[Rollup to session.total_cost]
    Rollup --> Broadcast[Broadcast Updates]
    
    style Calculate fill:#10B981
    style Broadcast fill:#F59E0B

---

5. Stop

Triggered when Claude finishes a turn (NOT when the session is closed).

Payload Example:

{
  "type": "stop",
  "sessionId": "sess_abc123",
  "stop_reason": "end_turn",
  "timestamp": "2024-03-18T12:05:00Z"
}

Purpose:

• Non-error: set main agent to idle and stamp awaiting_input_since (with awaiting_reason = stop) — Claude finished its turn, ball is in the user's court. The session shows as Waiting until UserPromptSubmit / PreToolUse fires
• Error (stop_reason="error"): drop awaiting_input_since (and awaiting_reason, cleared to NULL together), mark the session error
• Background subagents continue running — they complete individually via SubagentStop, never via Stop

Note: Stop does not fire when the user cancels a turn with Esc — interrupts emit no hook at all. The dashboard instead recovers cancelled turns from the transcript (see User interrupts (Esc)).

---

6. SubagentStop

Triggered when a sub-agent (explore, task, etc.) completes.

Payload Example:

{
  "type": "subagentStop",
  "sessionId": "sess_abc123",
  "agentId": "agent_explore_002",
  "agentType": "explore",
  "timestamp": "2024-03-18T12:03:00Z"
}

Purpose:

• Match the finishing subagent by description, type, or task and mark it completed
• Deliberately does NOT clear awaiting_input_since (nor awaiting_reason) — a backgrounded subagent finishing tells us nothing about whether the human has responded
• Triggers a fire-and-forget JSONL scan (scanAndImportSubagents from scripts/import-history.js) after res.json() returns. The scan walks the session's subagents/agent-*.jsonl files, pairs each assistant tool_use block with the next matching user tool_result block by tool_use_id, and emits per-tool PreToolUse + PostToolUse events under the subagent's own agent_id. Idempotent (data LIKE '%"tool_use_id":"X"%' dedup) and merges into a hook-created live row when one matches by subagent_type + started_at within 30 s — closes the gap where subagent-internal tool calls would otherwise be invisible to the dashboard
• Attributes per-subagent tokens to each subagent's OWN model (issue #185). Each subagent transcript carries its own msg.usage under its own msg.model; the scan writes those token buckets to token_usage keyed by the real model (e.g. a Haiku QA agent under an Opus orchestrator) so cost is no longer priced at the orchestrator's rate. The subagent's resolved model is also stamped onto its agent row (metadata.model). Buckets whose model equals the parent session's model are deliberately skipped here — that bucket is owned by the main-transcript writer, and double-writing it would trip replaceTokenUsage's compaction baseline-shift; same-model subagents are reconciled by the authoritative importSession / reconcileTokens path instead
• Rebuilds the nested-subagent hierarchy (reconcileSubagentParents). Subagent rows are inserted flat under the main agent because no single hook event or JSONL file carries the spawner's identity. Each subagent transcript, however, records every child it spawned via the Task tool as toolUseResult.agentId (surfaced by parseSubagentFile as spawnedChildren). The scan inverts these into a child→parent map and repoints parent_agent_id (via setAgentParent) so a subagent that spawns its own subagents nests under its true spawner instead of collapsing to a single level under main; any subagent no other subagent claims stays under main. Idempotent and additive (only rewrites parent_agent_id, never inserts/deletes), it also corrects the live PreToolUse-Agent parent heuristic's guesses once transcripts land. scanAndImportSubagents returns reparented alongside created; the SubagentStop refetch nudge fires when either is non-zero so a pure re-parent still refreshes the tree
• Imported tool events carry imported: true, source: "subagent_jsonl" in their JSON data payload so analytics can distinguish backfilled rows from live hook-captured ones if needed

---

7. Notification

Triggered when Claude Code sends a system notification.

Payload Example:

{
  "type": "notification",
  "sessionId": "sess_abc123",
  "notificationType": "backgroundTaskComplete",
  "message": "Explore agent completed successfully",
  "timestamp": "2024-03-18T12:03:00Z"
}

Purpose:

• Log the event for the activity feed
• If the message matches a permission/input-prompt pattern (permission, waiting for input, needs your approval, awaiting your response, …), stamp awaiting_input_since (with awaiting_reason = notification) so the session lands in Waiting
• If the message matches a compaction pattern, tag as a Compaction event
• Trigger a browser notification when the user has notifications enabled

---

8. SessionEnd

Triggered when a Claude Code session ends.

Payload Example:

{
  "type": "sessionEnd",
  "sessionId": "sess_abc123",
  "timestamp": "2024-03-18T14:30:00Z"
}

Purpose:

• Drop awaiting_input_since (and awaiting_reason, cleared to NULL together) on the session and any agents that still have it
• Mark all agents and the session as completed — unless the session is in error AND that error is still unrecovered at the transcript tail (isErrorAtTail: the latest API error has no successful turn after it), in which case error is preserved. A transient error the CLI retried past (successful assistant turns after the last error) finalizes as completed instead of freezing in a stale error
• Evict the session's transcript from the shared transcript cache

Stale-error self-heal. Separately from SessionEnd, the 15 s watchdog now scans error sessions (not just active) and clears a session back to active when its transcript has progressed past the last API error (isErrorAtTail is false). Claude auto-retries transient API errors (e.g. "Connection closed mid-response") and keeps working, so an error followed by real turn activity has recovered — recovery previously required a live UserPromptSubmit/PreToolUse hook, leaving imported or sweep-monitored sessions pinned in error indefinitely.

---

Hook Handler Implementation

hook-handler.js Architecture

graph TB
    CLI[CLI Args] --> Parse[Parse Hook Type]
    Stdin[stdin] --> ReadJSON[Read JSON]
    
    Parse --> HookType{Hook Type?}
    ReadJSON --> Payload[Event Payload]
    
    HookType -->|session-start| Endpoint1[POST /hooks/session-start]
    HookType -->|pre-tool-use| Endpoint2[POST /hooks/pre-tool-use]
    HookType -->|post-tool-use| Endpoint3[POST /hooks/post-tool-use]
    HookType -->|stop| Endpoint4[POST /hooks/stop]
    HookType -->|subagent-stop| Endpoint5[POST /hooks/subagent-stop]
    HookType -->|notification| Endpoint6[POST /hooks/notification]
    HookType -->|session-end| Endpoint7[POST /hooks/session-end]
    
    Payload --> Endpoint1
    Payload --> Endpoint2
    Payload --> Endpoint3
    Payload --> Endpoint4
    Payload --> Endpoint5
    Payload --> Endpoint6
    Payload --> Endpoint7
    
    Endpoint1 --> HTTP[HTTP POST]
    Endpoint2 --> HTTP
    Endpoint3 --> HTTP
    Endpoint4 --> HTTP
    Endpoint5 --> HTTP
    Endpoint6 --> HTTP
    Endpoint7 --> HTTP
    
    HTTP --> Response{Success?}
    Response -->|Yes| Exit0[exit 0]
    Response -->|No| Exit1[exit 1]
    
    style HTTP fill:#10B981
    style Exit0 fill:#10B981
    style Exit1 fill:#EF4444

Implementation

#!/usr/bin/env node
// scripts/hook-handler.js

const http = require('http');
const fs = require('fs');

const HOOK_TYPE = process.argv[2];
const SERVER_URL = 'http://localhost:4820';
const TIMEOUT = 5000; // 5s timeout

// Read JSON from stdin
let inputData = '';
process.stdin.setEncoding('utf8');
process.stdin.on('data', (chunk) => inputData += chunk);

process.stdin.on('end', () => {
  try {
    const payload = JSON.parse(inputData);
    sendToServer(HOOK_TYPE, payload);
  } catch (err) {
    console.error('[hook-handler] JSON parse error:', err);
    process.exit(1);
  }
});

function sendToServer(hookType, payload) {
  const postData = JSON.stringify(payload);
  
  const options = {
    hostname: 'localhost',
    port: 4820,
    path: `/hooks/${hookType}`,
    method: 'POST',
    headers: {
      'Content-Type': 'application/json',
      'Content-Length': Buffer.byteLength(postData)
    },
    timeout: TIMEOUT
  };
  
  const req = http.request(options, (res) => {
    let responseData = '';
    res.on('data', (chunk) => responseData += chunk);
    res.on('end', () => {
      if (res.statusCode === 200) {
        process.exit(0);
      } else {
        console.error(`[hook-handler] Server error: ${res.statusCode}`);
        process.exit(1);
      }
    });
  });
  
  req.on('error', (err) => {
    console.error('[hook-handler] Request error:', err);
    process.exit(1);
  });
  
  req.on('timeout', () => {
    console.error('[hook-handler] Request timeout');
    req.destroy();
    process.exit(1);
  });
  
  req.write(postData);
  req.end();
}

Port resolution & fan-out. The snippet above shows a single fixed 4820 for clarity. The real scripts/hook-handler.js resolves hook targets at runtime via server/lib/server-info.js:

1. If CLAUDE_DASHBOARD_PORT is set in the environment, the handler treats it as an explicit operator override and POSTs to that single port — no discovery, no fan-out (useful for tests and container setups).
2. Otherwise it reads ~/.claude/.agent-dashboard.json, a JSON document that lists every dashboard server currently running on the machine. Each server appends its {port, pid, startedAt, dataDir} entry on startup and removes it on a clean shutdown. The handler prunes any entry whose PID is no longer alive and POSTs the hook payload to one port per unique SQLite data directory (lowest port wins when Docker and npm run dev share ~/.claude/agent-dashboard).
3. If neither yields a target, the handler falls back to 4820.

Dashboards with different databases (e.g. the packaged desktop app using its own Application Support data dir alongside npm run dev) still each receive hooks. Dashboards sharing one database never double-ingest events.

---

Event Processing

Server-Side Hook Processing

// server/routes/hooks.js

router.post('/session-start', (req, res) => {
  try {
    const { sessionId, model, agentId, agentType } = req.body;
    
    // Upsert session
    let session = stmts.findSession.get(sessionId);
    if (!session) {
      stmts.createSession.run(sessionId, model);
      session = stmts.findSession.get(sessionId);
      broadcast({ type: 'session.created', data: session });
    }
    
    // Create main agent
    if (!stmts.findAgent.get(agentId)) {
      stmts.createAgent.run(agentId, sessionId, agentType);
      const agent = stmts.findAgent.get(agentId);
      broadcast({ type: 'agent.created', data: agent });
    }
    
    // Touch session (update updated_at)
    stmts.touchSession.run(sessionId);
    
    res.json({ success: true });
  } catch (err) {
    console.error('session-start error:', err);
    res.json({ success: false, error: err.message });
  }
});

Event Processing Pipeline

graph TB
    Hook[Hook Event] --> Validate[Validate Payload]
    Validate --> DB[Database Operations]
    DB --> Session[Update Session]
    DB --> Agent[Update Agent]
    DB --> Tool[Create Tool Record]
    
    Session --> Broadcast[Broadcast to WebSocket]
    Agent --> Broadcast
    Tool --> Broadcast
    
    Broadcast --> Client1[Client 1]
    Broadcast --> Client2[Client 2]
    Broadcast --> ClientN[Client N]
    
    style Validate fill:#3B82F6
    style DB fill:#003B57,color:#fff
    style Broadcast fill:#F59E0B

Transcript-derived sync

On every event that carries a transcript_path, the shared TranscriptCache re-reads the JSONL (incrementally) and the ingestor keeps three session fields in sync with what the user is actually doing in the CLI:

• Tokens / cost — usage is accumulated per model bucket (compaction-aware baselines).
• Model — the most recent assistant entry's model keeps sessions.model current after a /model switch.
• Name — the session title is read from the transcript: the custom-title line (/rename, claude -n, picker Ctrl+R) always wins, otherwise the auto-generated ai-title fills a placeholder/auto name (so a user-chosen name is never clobbered). When neither title exists, the session's first user prompt (tool-result, meta/caveat, and slash-command plumbing entries skipped; whitespace-collapsed, 60-char label) fills the placeholder session name plus the main agent's placeholder name and empty task — a later ai-title can still replace a descriptor-filled name, and the agent fill passes the in-flight current_tool through so it is never wiped mid-turn. sessions.name is updated via a no-op-guarded statement and a session_updated broadcast fires only on a real change, so the dashboard reflects renames in real time. The 15 s error-detection watchdog runs the same sync for active sessions left idle right after a /rename.

User interrupts (Esc) — no hook fires

Cancelling a turn with Esc fires no hook at all (a documented Claude Code limitation — there is no Stop, Notification, or other event on interrupt). Since UserPromptSubmit has already promoted the main agent to working, an un-handled cancel would leave the session stuck in working indefinitely. The dashboard recovers it from the transcript, via the same 15 s watchdog, two ways:

1. Marker path — when the cancel happens after some output, Claude Code appends a [Request interrupted by user] user entry (with an interruptedMessageId). TranscriptCache reports pendingInterrupt, computed from transcript ordering alone: the latest interrupt timestamp vs the latest real turn activity, both on Claude Code's clock. (It is not compared against the session's last hook event — those clocks differ, and for a sub-second cancel the UserPromptSubmit event is recorded after the transcript interrupt, the precise case that used to stay stuck.) The session moves to Waiting within ~15 s.
2. Idle-working timeout — when Esc is pressed before any output, Claude Code writes no marker; the only evidence is silence. When the main agent has been working with current_tool null and neither a hook event nor the transcript mtime has advanced for DASHBOARD_WORKING_IDLE_SECONDS (default 120), the turn is treated as dead. A streaming/long-output turn (transcript still growing) and an in-flight tool call are exempt by those guards; a rare false flip self-heals on the next real hook.

Both paths land the session in Waiting (main agent → waiting, awaiting_input_since stamped with awaiting_reason = interrupted — identical to a non-error Stop aside from the reason) and log an Interrupted event. A resume (new prompt in the transcript) clears pendingInterrupt and the fresh hook keeps the session non-stale.

Missed SessionEnd (dashboard down) — liveness reap

SessionEnd is the only signal that a session closed, and hooks are fire-and-forget: if the dashboard was not running when the user quit (Ctrl+C, terminal closed), the POST fails silently and the event is lost forever — the session previously sat in Waiting until the stale sweep (3 h by default). The same 15 s watchdog closes the gap with a process-liveness probe (server/lib/session-liveness.js): it enumerates running claude CLI processes and their working directories (ps + lsof on macOS, /proc/<pid>/cwd on Linux) and completes any active session whose cwd has no live claude process — the same terminal state a real SessionEnd produces, plus a synthetic SessionEnd event (data.source = "liveness-probe") on the timeline.

Fail-safe guards: the probe reports "no answer" (nothing changes) on Windows, inside containers (host processes are invisible), on ps/lsof failure, or when disabled via DASHBOARD_LIVENESS_PROBE=0 (the escape hatch for hooks arriving from another machine); the session must have a cwd, and that cwd must be POSIX-absolute — a household-hook-forwarded session reports the origin machine's own path (e.g. a Windows D:\Git\ai-deck) that this host's /proc/lsof scan can never produce, so the reap skips it rather than falsely completing every remote session (this makes a mixed local + forwarded deployment correct without the blanket DASHBOARD_LIVENESS_PROBE=0); Remote Data Source sessions (sessions.source ≠ local) are also skipped outright — their POSIX-absolute cwd lives on another machine reached over SSH, so this host's process probe proves nothing about them, and their status is reconciled from the SSH mirror by remote-sync.js (the same source = 'local' guard also exempts them from the watchdog's error/interrupt scan and both stale sweeps); and — on watchdog ticks only — its transcript must not have been written for at least DASHBOARD_LIVENESS_IDLE_SECONDS (default 60; the last hook write is the fallback clock when no transcript exists on disk) so a mid-turn / just-resumed session never flickers out. The reap runs immediately at startup (rows from a previous run), again ~5 s after startup (rows the startup sync just imported) — both startup passes skip the idle gate, so a session quit even seconds before launch clears at once — and on every 15 s watchdog tick (gated) as the safety net. A false completion self-heals — the next hook event reactivates the session.

---

Error Handling

Error Handling Strategy

graph TB
    Error[Error Occurs] --> Type{Error Type?}
    
    Type -->|Network Error| Retry[Retry Once]
    Type -->|Timeout| Log1[Log + Exit 1]
    Type -->|Parse Error| Log2[Log + Exit 1]
    Type -->|Server Error| Log3[Log + Exit 1]
    
    Retry --> Success{Success?}
    Success -->|Yes| Exit0[Exit 0]
    Success -->|No| Exit1[Exit 1]
    
    Log1 --> Exit1
    Log2 --> Exit1
    Log3 --> Exit1
    
    style Exit0 fill:#10B981
    style Exit1 fill:#EF4444

Hook Script Error Handling

#!/usr/bin/env python3
# .githooks/session-start.py

import sys
import json
import subprocess
import logging

logging.basicConfig(
    filename='.githooks/hooks.log',
    level=logging.ERROR,
    format='%(asctime)s - %(levelname)s - %(message)s'
)

try:
    data = json.load(sys.stdin)
    
    result = subprocess.run(
        ['node', 'scripts/hook-handler.js', 'session-start'],
        input=json.dumps(data),
        text=True,
        timeout=5,
        capture_output=True
    )
    
    if result.returncode != 0:
        logging.error(f'Hook handler failed: {result.stderr}')
    
except Exception as e:
    logging.error(f'Hook error: {str(e)}')

# Always exit 0 to avoid blocking Claude Code
sys.exit(0)

---

Performance Considerations

Hook Execution Time

graph TB
    subgraph "Hook Execution Breakdown"
        Python[Python Script<br/>~10ms]
        Handler[Node Handler<br/>~20ms]
        HTTP[HTTP POST<br/>~30ms]
        DB[Database Write<br/>~5ms]
        WS[WebSocket Broadcast<br/>~5ms]
    end
    
    Total[Total: ~70ms]
    
    Python --> Handler
    Handler --> HTTP
    HTTP --> DB
    DB --> WS
    WS --> Total
    
    style Total fill:#10B981

Performance Targets:

Phase	Target	Actual
Hook script	< 20ms	~10ms
Handler	< 30ms	~20ms
HTTP POST	< 50ms	~30ms
Database	< 10ms	~5ms
Total	< 100ms	~70ms

Optimization Techniques

graph TB
    subgraph "Optimizations"
        Async[Async HTTP<br/>Don't wait for response]
        Batch[Batch Updates<br/>Transaction batching]
        Index[Database Indexes<br/>Fast lookups]
        Pool[Connection Pooling<br/>Reuse connections]
    end
    
    Async --> Faster[Faster Hook Execution]
    Batch --> Faster
    Index --> Faster
    Pool --> Faster
    
    style Faster fill:#10B981

---

Testing Hooks

Manual Testing

# Test session-start hook
echo '{"type":"sessionStart","sessionId":"test_001","model":"claude-sonnet-4","agentId":"agent_test","agentType":"general-purpose"}' | \
  python3 .githooks/session-start.py

# Test pre-tool-use hook
echo '{"type":"preToolUse","sessionId":"test_001","agentId":"agent_test","toolName":"bash"}' | \
  python3 .githooks/pre-tool-use.py

# Test post-tool-use hook
echo '{"type":"postToolUse","sessionId":"test_001","agentId":"agent_test","toolName":"bash","durationMs":100,"success":true,"inputTokens":1000,"outputTokens":500}' | \
  python3 .githooks/post-tool-use.py

Integration Testing

// server/__tests__/hooks.test.js
import { test } from 'node:test';
import assert from 'node:assert';

test('session-start hook creates session', async () => {
  const payload = {
    sessionId: 'test_session',
    model: 'claude-sonnet-4',
    agentId: 'test_agent',
    agentType: 'general-purpose'
  };
  
  const response = await fetch('http://localhost:4820/hooks/session-start', {
    method: 'POST',
    headers: { 'Content-Type': 'application/json' },
    body: JSON.stringify(payload)
  });
  
  const data = await response.json();
  assert.strictEqual(data.success, true);
  
  // Verify session exists
  const session = await fetch('http://localhost:4820/api/sessions/test_session');
  assert.strictEqual(session.status, 200);
});

---

Troubleshooting

Common Issues

Issue	Symptoms	Solution
Hooks not executing	No data in dashboard	Check .githooks/ exists and scripts are executable
Timeout errors	Hooks take >5s	Check server is running, reduce timeout
Parse errors	JSON parse failed	Validate hook payload format
Permission denied	Hook script won't run	chmod +x .githooks/*.py
Server connection refused	HTTP POST fails	Start dashboard server (npm start)

Debug Mode

# Enable hook logging
export DASHBOARD_DEBUG=1

# Run hook manually with verbose output
python3 -u .githooks/session-start.py < test-payload.json

Health Check

# Check server is running
curl http://localhost:4820/api/sessions

# Expected: {"sessions": [...]}

---

Summary

The hook system provides:

• ✅ Real-time event capture - Lifecycle, tools, notifications
• ✅ Non-blocking execution - Never delays Claude Code
• ✅ Fail-safe design - Errors don't stop execution
• ✅ Fast processing - < 100ms per hook
• ✅ Complete coverage - All agent lifecycle events
• ✅ Easy installation - One-command setup

For server-side processing, see server/README.md.