feat(web4-governance): add governance plugin with R6 workflow (Tiers 1-4)

Web4 governance plugin for Claude Code hooks — structured audit trails,
trust tensors, entity witnessing, policy gating, and event streaming.

Tiers: observational audit (T1), policy presets and rate limiting (T1.5),
signing and persistent witnesses (T2), multi-target extraction (T3),
event stream monitoring (T4).

See plugins/web4-governance/README.md for full documentation.
PR: #20448

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: dp-web4

.gitignore

@@ -1,2 +1,8 @@
 .DS_Store
 
+*.ffs_db
+.gitnexus
+.claude/skills/gitnexus/
+CLAUDE.md
+AGENTS.md
+__pycache__/

plugins/web4-governance/.claude-plugin/plugin.json

@@ -0,0 +1,12 @@
+{
+  "name": "web4-governance",
+  "version": "1.0.0",
+  "description": "Lightweight AI governance with R6 workflow formalism and audit trails. Every tool call becomes a structured request with verifiable provenance.",
+  "author": {
+    "name": "Web4 Contributors",
+    "email": "web4@metalinxx.io"
+  },
+  "repository": "https://github.com/dp-web4/web4",
+  "keywords": ["governance", "audit", "trust", "r6", "provenance", "web4"],
+  "license": "MIT"
+}

plugins/web4-governance/.gitattributes

@@ -0,0 +1,8 @@
+# Force LF line endings for scripts (critical for shebang on Unix/WSL)
+*.py text eol=lf
+*.sh text eol=lf
+
+# Other text files can use native line endings
+*.md text
+*.json text
+*.txt text

plugins/web4-governance/EVENT_STREAM_API.md

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+# Event Stream API
+
+Real-time monitoring endpoint for the Web4 Governance plugin.
+
+## Overview
+
+The event stream provides a JSONL (JSON Lines) file that external clients can tail for real-time monitoring, alerting, and analytics.
+
+**Stream Location**: `~/.web4/events.jsonl`
+
+## Quick Start
+
+### Tail the stream (real-time)
+```bash
+tail -f ~/.web4/events.jsonl | jq .
+```
+
+### Filter by severity
+```bash
+tail -f ~/.web4/events.jsonl | jq -c 'select(.severity == "alert")'
+```
+
+### Filter by event type
+```bash
+grep '"type":"policy_decision"' ~/.web4/events.jsonl | jq .
+```
+
+### Python consumer
+```python
+import json
+
+with open("~/.web4/events.jsonl", "r") as f:
+    for line in f:
+        event = json.loads(line)
+        if event.get("severity") == "alert":
+            print(f"ALERT: {event.get('reason')}")
+```
+
+---
+
+## Event Schema
+
+Each line in the stream is a self-contained JSON object:
+
+```json
+{
+  "type": "policy_decision",
+  "timestamp": "2026-02-05T10:30:00.123456+00:00",
+  "severity": "alert",
+  "session_id": "sess-abc123",
+  "tool": "Bash",
+  "target": "rm -rf /tmp/test",
+  "category": "command",
+  "decision": "deny",
+  "reason": "Destructive command blocked by safety preset",
+  "rule_id": "deny-destructive-commands"
+}
+```
+
+### Required Fields
+
+| Field | Type | Description |
+|-------|------|-------------|
+| `type` | string | Event type (see Event Types below) |
+| `timestamp` | string | ISO 8601 UTC timestamp |
+| `severity` | string | Severity level: `debug`, `info`, `warn`, `alert`, `error` |
+
+### Optional Context Fields
+
+| Field | Type | Description |
+|-------|------|-------------|
+| `session_id` | string | Session identifier |
+| `agent_id` | string | Agent/role identifier |
+
+### Event-Specific Fields
+
+| Field | Type | Description |
+|-------|------|-------------|
+| `tool` | string | Tool name (Bash, Read, Edit, etc.) |
+| `target` | string | Target path, URL, or command |
+| `category` | string | Tool category (file_read, file_write, command, network, etc.) |
+| `decision` | string | Policy decision: `allow`, `deny`, `warn` |
+| `reason` | string | Human-readable explanation |
+| `rule_id` | string | ID of matched policy rule |
+
+### Metrics Fields
+
+| Field | Type | Description |
+|-------|------|-------------|
+| `duration_ms` | integer | Operation duration in milliseconds |
+| `count` | integer | Generic count (rate limits, etc.) |
+
+### Trust Fields
+
+| Field | Type | Description |
+|-------|------|-------------|
+| `trust_before` | float | Trust value before update (0.0-1.0) |
+| `trust_after` | float | Trust value after update (0.0-1.0) |
+| `trust_delta` | float | Change in trust value |
+
+### Error Fields
+
+| Field | Type | Description |
+|-------|------|-------------|
+| `error` | string | Error message |
+| `error_type` | string | Error class/type |
+
+### Extensible Metadata
+
+| Field | Type | Description |
+|-------|------|-------------|
+| `metadata` | object | Additional key-value data |
+
+---
+
+## Event Types
+
+### Session Lifecycle
+
+| Type | Severity | Description |
+|------|----------|-------------|
+| `session_start` | info | New session started |
+| `session_end` | info | Session ended |
+
+**Example:**
+```json
+{"type":"session_start","timestamp":"2026-02-05T10:00:00Z","severity":"info","session_id":"sess-abc123","metadata":{"project":"my-app","atp_budget":100}}
+```
+
+### Tool Execution
+
+| Type | Severity | Description |
+|------|----------|-------------|
+| `tool_call` | info | Tool invocation started |
+| `tool_result` | info | Tool completed |
+
+**Example:**
+```json
+{"type":"tool_call","timestamp":"2026-02-05T10:01:00Z","severity":"info","session_id":"sess-abc123","tool":"Read","target":"/app/src/main.py","category":"file_read"}
+```
+
+### Policy Decisions
+
+| Type | Severity | Description |
+|------|----------|-------------|
+| `policy_decision` | varies | Policy evaluated (info=allow, warn=warn, alert=deny) |
+| `policy_violation` | alert | Policy rule violated |
+
+**Example (deny):**
+```json
+{"type":"policy_decision","timestamp":"2026-02-05T10:02:00Z","severity":"alert","session_id":"sess-abc123","tool":"Bash","target":"rm -rf /","decision":"deny","reason":"Destructive command blocked by safety preset","rule_id":"deny-destructive-commands"}
+```
+
+**Example (warn):**
+```json
+{"type":"policy_decision","timestamp":"2026-02-05T10:03:00Z","severity":"warn","session_id":"sess-abc123","tool":"Bash","target":"rm temp.txt","decision":"warn","reason":"File deletion flagged - use with caution","rule_id":"warn-file-delete"}
+```
+
+### Rate Limiting
+
+| Type | Severity | Description |
+|------|----------|-------------|
+| `rate_limit_check` | debug | Rate limit checked |
+| `rate_limit_exceeded` | alert | Rate limit exceeded |
+
+**Example:**
+```json
+{"type":"rate_limit_exceeded","timestamp":"2026-02-05T10:04:00Z","severity":"alert","session_id":"sess-abc123","target":"ratelimit:bash:tool","count":6,"metadata":{"max_count":5}}
+```
+
+### Trust Updates
+
+| Type | Severity | Description |
+|------|----------|-------------|
+| `trust_update` | info | Agent trust level changed |
+
+**Example:**
+```json
+{"type":"trust_update","timestamp":"2026-02-05T10:05:00Z","severity":"info","session_id":"sess-abc123","agent_id":"code-reviewer","trust_before":0.5,"trust_after":0.55,"trust_delta":0.05,"reason":"Successful code review"}
+```
+
+### Agent Lifecycle
+
+| Type | Severity | Description |
+|------|----------|-------------|
+| `agent_spawn` | info | Agent spawned |
+| `agent_complete` | info | Agent completed |
+
+**Example:**
+```json
+{"type":"agent_spawn","timestamp":"2026-02-05T10:06:00Z","severity":"info","session_id":"sess-abc123","agent_id":"test-runner","metadata":{"capabilities":{"can_write":true,"can_execute":true}}}
+```
+
+### Audit Events
+
+| Type | Severity | Description |
+|------|----------|-------------|
+| `audit_record` | info | Standard audit record |
+| `audit_alert` | alert | High-priority audit event (credential access, etc.) |
+
+**Example (credential access alert):**
+```json
+{"type":"audit_alert","timestamp":"2026-02-05T10:07:00Z","severity":"alert","session_id":"sess-abc123","tool":"Read","target":"/home/user/.aws/credentials","category":"credential_access","reason":"Credential file access detected"}
+```
+
+### System Events
+
+| Type | Severity | Description |
+|------|----------|-------------|
+| `system_info` | info | System information |
+| `system_error` | error | System error |
+
+**Example:**
+```json
+{"type":"system_error","timestamp":"2026-02-05T10:08:00Z","severity":"error","error":"Database connection failed","error_type":"sqlite3.OperationalError"}
+```
+
+---
+
+## Severity Levels
+
+| Level | When Used | Action |
+|-------|-----------|--------|
+| `debug` | Verbose debugging | Usually filtered |
+| `info` | Normal operations | Log/monitor |
+| `warn` | Potential issues | Review |
+| `alert` | Security events, policy violations | Immediate attention |
+| `error` | System errors | Investigate |
+
+---
+
+## File Rotation
+
+The stream file automatically rotates at 100MB:
+- Current: `~/.web4/events.jsonl`
+- Rotated: `~/.web4/events.jsonl.1`
+
+Only one backup is kept. For long-term retention, configure an external log collector.
+
+---
+
+## Integration Examples
+
+### Forward to syslog
+```bash
+tail -f ~/.web4/events.jsonl | while read line; do
+  logger -t web4-governance "$line"
+done
+```
+
+### Send alerts to Slack
+```python
+import json
+import requests
+
+WEBHOOK_URL = "https://hooks.slack.com/services/..."
+
+with open("~/.web4/events.jsonl", "r") as f:
+    f.seek(0, 2)  # Seek to end
+    while True:
+        line = f.readline()
+        if line:
+            event = json.loads(line)
+            if event.get("severity") == "alert":
+                requests.post(WEBHOOK_URL, json={
+                    "text": f":warning: {event.get('type')}: {event.get('reason')}"
+                })
+```
+
+### Prometheus metrics (conceptual)
+```python
+from prometheus_client import Counter
+
+policy_decisions = Counter('web4_policy_decisions', 'Policy decisions', ['decision'])
+
+# In your event consumer:
+if event["type"] == "policy_decision":
+    policy_decisions.labels(decision=event["decision"]).inc()
+```
+
+### Structured logging (JSON to stdout)
+```bash
+tail -f ~/.web4/events.jsonl | jq -c '{
+  time: .timestamp,
+  level: .severity,
+  msg: .reason // .type,
+  tool: .tool,
+  session: .session_id
+}'
+```
+
+---
+
+## Configuration
+
+The event stream can be configured when initializing:
+
+```python
+from governance.event_stream import EventStream, Severity
+
+# Custom location and minimum severity
+stream = EventStream(
+    storage_path="~/.my-app/governance",
+    filename="audit-events.jsonl",
+    min_severity=Severity.WARN  # Only emit WARN and above
+)
+```
+
+---
+
+## Best Practices
+
+1. **Use `tail -f`** for real-time monitoring rather than polling
+2. **Filter by severity** to reduce noise (`alert` for critical events)
+3. **Use `jq`** for ad-hoc queries and formatting
+4. **Configure external log rotation** for long-term retention
+5. **Register callbacks** for in-process alerting (low latency)
+
+---
+
+## Version History
+
+| Version | Changes |
+|---------|---------|
+| 0.4.0 | Initial event stream API |