feat: Phase F-1 — Plexum-fabric-channel-plugin foundation

Ports the foundation of Fabric.OpenclawPlugin to a native Plexum
channel plugin (Go). F-2+ phases (socket.io inbound, wakeup gate,
tools, presence, etc.) follow.

Layout:
  internal/identity/      — fabric-identity.json registry (agent → API key)
  internal/fabric/        — REST client (Center auth + Guild messaging)
  internal/config/        — channels/<name>.json fabric extension parser
  cmd/plexum-fabric-register/      — agent registration CLI
  cmd/plexum-fabric-channel-plugin/— Plexum SDK plugin entry
  scripts/install.sh      — build + install + manifest generator

Plugin behavior (F-1):
- Reads <profile>/channels/*.json, filters plugin=plexum-fabric-channel,
  builds (plexum-channel-name → fabric channel-id) index
- Validates each bound agent's API key against Center at init
  (warmSessions); logs warning but doesn't refuse init on bad keys
- `send` MCP tool: POST plain text to the bound Fabric channel as the
  agent user; selects guild endpoint+token from cached session
- Manifest channels[] is generated by install.sh from current
  channels/*.json — re-run with --reset-manifest after adding bindings
- Plugin-private config at
  <profile>/plugins/plexum-fabric-channel/config.json
  (center_api_base, default http://localhost:7001/api)

Live smoke verified:
- plexum-fabric-register against running Fabric Center (port 7001):
  validated fak_..., wrote identity file with user_id + email captured

Tests: identity (5) + config (6) = 11 unit tests.

F-2 will hook socket.io for inbound + wakeup gating + token refresh.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

README.md

@@ -0,0 +1,85 @@
+# Plexum-fabric-channel-plugin
+
+Native Plexum channel plugin connecting Plexum agents to **Fabric** guilds as
+real channel members. Inspired by `Fabric.OpenclawPlugin` — Plexum port,
+delivered in phases.
+
+## Status
+
+**Phase F-1 (foundation) — current**: identity registry, Center auth, REST
+client, plugin scaffold, channel-binding discovery. The `send` outbound tool
+posts plain text to a Fabric channel as the bound agent.
+
+**Phase F-2 (deferred)**: socket.io inbound, wakeup-gated dispatch, token
+refresh, per-channel serial queue.
+
+**Phase F-3+ (deferred)**: tools.ts port (~15 MCP tools — channel/canvas/
+sub-discussion/etc.), presence sync, command sync, attachments, coalesce
+parity.
+
+## Install
+
+```bash
+cd ~/Plexum-fabric-channel-plugin
+./scripts/install.sh                  # build + install plugin + register CLI
+```
+
+Then:
+
+1. **Mint a Center API key** for each Plexum agent that should speak in Fabric:
+   ```bash
+   docker exec fabric-backend-center node dist/cli.js user apikey --email <agent-email>
+   ```
+
+2. **Register the key** with Plexum:
+   ```bash
+   plexum-fabric-register --agent-id alice --api-key fak_xxxx
+   # writes ~/.plexum/fabric-identity.json
+   ```
+
+3. **Configure plugin-level settings** at
+   `~/.plexum/plugins/plexum-fabric-channel/config.json`:
+   ```json
+   {
+     "center_api_base": "http://localhost:7001/api"
+   }
+   ```
+
+4. **Bind a Plexum channel name to a Fabric channel** at
+   `~/.plexum/channels/<plexum-channel-name>.json`:
+   ```json
+   {
+     "agent_id": "alice",
+     "plugin": "plexum-fabric-channel",
+     "fabric": {
+       "guild_node_id": "test-guild1",
+       "channel_id": "ch_xxxxxxxxx"
+     }
+   }
+   ```
+
+5. **Allow the plugin** in `~/.plexum/plexum.json`:
+   ```json
+   {"plugins": {"allow": ["plexum-fabric-channel"]}}
+   ```
+
+6. **Restart the gateway**: `systemctl --user restart plexum`
+
+## What you get in F-1
+
+- Plugin loads at gateway start, validates every bound agent's API key
+  against Center via `agentLogin`, and warms a session per agent.
+- `send` MCP tool posts plain text to the bound Fabric channel as the
+  agent user.
+- No inbound yet — Fabric → Plexum routing arrives in F-2.
+
+## Build manually
+
+```bash
+go build -o bin/plexum-fabric-channel-plugin ./cmd/plexum-fabric-channel-plugin
+go build -o bin/plexum-fabric-register      ./cmd/plexum-fabric-register
+```
+
+## License
+
+Same as Plexum.