docs(devrel): Lark/Feishu channel tutorial for PR #480

docs/tutorials/lark-feishu-channel.md

@@ -0,0 +1,95 @@
+# Connecting an AI Agent to Lark / Feishu
+
+Molecule AI's Lark channel adapter (shipped in #480) lets any workspace agent
+receive messages from Lark or Feishu chats and reply through the same thread.
+This tutorial gets you from zero to a live bot in about ten minutes.
+
+> **Lark vs Feishu** — same payload format, different host.
+> Lark is the international product; Feishu is the China edition.
+> The adapter detects which host to use from your webhook URL.
+
+## Prerequisites
+
+- A Molecule AI workspace already running (any runtime)
+- A Lark tenant with permission to create a **Custom Bot**
+- `PLATFORM_URL` and a workspace bearer token
+
+## Setup
+
+```bash
+# 1. Create a Lark Custom Bot in your group chat
+#    Settings → Bots → Add Bot → Custom Bot
+#    Copy the Webhook URL — looks like:
+#    https://open.larksuite.com/open-apis/bot/v2/hook/<token>
+
+# 2. (Recommended) Set a Verification Token in the Lark bot settings.
+#    This lets the platform reject spoofed inbound messages.
+
+# 3. Register the channel on your workspace
+curl -s -X POST "${PLATFORM_URL}/workspaces/${WORKSPACE_ID}/channel" \
+  -H "Authorization: Bearer ${TOKEN}" \
+  -H "Content-Type: application/json" \
+  -d '{
+    "type": "lark",
+    "config": {
+      "webhook_url": "https://open.larksuite.com/open-apis/bot/v2/hook/YOUR_TOKEN",
+      "verify_token": "YOUR_VERIFY_TOKEN"
+    }
+  }'
+
+# 4. Point Lark Event Subscriptions at your platform
+#    Lark Developer Console → Event Subscriptions → Request URL:
+#    https://YOUR_PLATFORM/channels/lark/webhook
+
+# 5. Subscribe to the im.message.receive_v1 event in Lark console.
+
+# 6. Send a message in the Lark group — your agent replies.
+#    Watch the round-trip:
+molecule workspace logs ${WORKSPACE_ID} --follow
+```
+
+## The 200-OK-but-failed gotcha
+
+Lark's outbound API **always** returns HTTP 200, even on delivery failure.
+The real result is in the JSON body:
+
+```json
+{ "code": 99, "msg": "...", "data": {} }
+```
+
+Molecule AI surfaces `code != 0` as a hard Go error so your agent sees an
+actual failure instead of silent data loss. Check `last_sample_error` on the
+workspace if messages seem to disappear.
+
+## Expected output
+
+After step 6, `workspace logs` shows:
+
+```
+[channel:lark] inbound  user_id=ou_xxx  text="Hello agent"
+[agent]        reply    "Hi! How can I help you today?"
+[channel:lark] outbound code=0  ok
+```
+
+## How it works
+
+When a Lark user sends a message the platform receives a `v2 event_callback`
+(`im.message.receive_v1`). It validates the optional `verify_token` with a
+constant-time compare (timing-attack safe), then proxies the text through the
+standard A2A flow — the same path used by Telegram and Slack. The agent never
+knows which channel it's talking to. Replies go back via the Custom Bot
+webhook; the adapter prefers `user_id` over `open_id` so replies land in the
+correct DM thread when the bot has contacts permission.
+
+## Multi-channel teams
+
+You can attach different channels to different workspaces in the same org.
+Route customer-facing chats to a triage agent on Lark while your eng team
+talks to the DevOps agent on Slack — all coordinated through the same
+Molecule AI canvas without code changes.
+
+## Related
+
+- PR #480: [feat(channels): Lark / Feishu channel adapter](https://github.com/Molecule-AI/molecule-core/pull/480)
+- [Social channels architecture](../agent-runtime/social-channels.md)
+- [Channel adapter reference](../api-reference.md#channels)