feat(photon): add agent-facing emoji reaction support

Add `action='react'` to `send_message` tool and expose `add_reaction`/
`remove_reaction` on the Photon adapter.

- Track latest inbound message id per chat (`_last_inbound_by_chat`,
  bounded to 200 entries) so the agent can react without threading
  message ids through tool calls
- New `add_reaction`/`remove_reaction` public methods on PhotonAdapter;
  unlike the lifecycle tapbacks, these are not gated by PHOTON_REACTIONS
- `send_message` gains `action='react'` with `emoji` and optional
  `message_id` params; resolves target via existing channel-directory
  and home-channel logic; requires a live gateway adapter

tools/send_message_tool.py

@@ -138,8 +138,8 @@ SEND_MESSAGE_SCHEMA = {
         "properties": {
             "action": {
                 "type": "string",
-                "enum": ["send", "list"],
-                "description": "Action to perform. 'send' (default) sends a message. 'list' returns all available channels/contacts across connected platforms."
+                "enum": ["send", "list", "react"],
+                "description": "Action to perform. 'send' (default) sends a message. 'list' returns all available channels/contacts across connected platforms. 'react' attaches an emoji reaction to a message (platforms that support it, e.g. photon/iMessage tapbacks)."
             },
             "target": {
                 "type": "string",
@@ -148,6 +148,14 @@ SEND_MESSAGE_SCHEMA = {
             "message": {
                 "type": "string",
                 "description": "The message text to send. To send an image or file, include MEDIA:<local_path> (e.g. 'MEDIA:/tmp/report.pdf') in the message — the platform will deliver it as a native media attachment."
+            },
+            "emoji": {
+                "type": "string",
+                "description": "For action='react': the emoji to react with (e.g. '❤️'). On iMessage, ❤️👍👎😂‼️❓ render as native tapbacks; other emoji use custom-emoji reactions."
+            },
+            "message_id": {
+                "type": "string",
+                "description": "For action='react': id of the message to react to. Omit to react to the most recent message received in that chat (usually the one being replied to)."
             }
         },
         "required": []
@@ -162,6 +170,9 @@ def send_message_tool(args, **kw):
     if action == "list":
         return _handle_list()
 
+    if action == "react":
+        return _handle_react(args)
+
     return _handle_send(args)
 
 
@@ -174,6 +185,88 @@ def _handle_list():
         return json.dumps(_error(f"Failed to load channel directory: {e}"))
 
 
+def _handle_react(args):
+    """Attach an emoji reaction to a message via a live gateway adapter.
+
+    Only adapters that expose an ``add_reaction(chat_id, emoji, message_id)``
+    coroutine support this (e.g. photon/iMessage tapbacks). Requires the
+    gateway to be running in this process — there is no standalone fallback,
+    since reacting needs the adapter's live message-id state.
+    """
+    target = args.get("target", "")
+    emoji = (args.get("emoji") or "").strip()
+    message_id = (args.get("message_id") or "").strip() or None
+    if not target or not emoji:
+        return tool_error(
+            "Both 'target' and 'emoji' are required when action='react'"
+        )
+
+    parts = target.split(":", 1)
+    platform_name = parts[0].strip().lower()
+    target_ref = parts[1].strip() if len(parts) > 1 else None
+    chat_id = None
+    if target_ref:
+        chat_id, _thread_id, _ = _parse_target_ref(platform_name, target_ref)
+        if not chat_id:
+            try:
+                from gateway.channel_directory import resolve_channel_name
+                resolved = resolve_channel_name(platform_name, target_ref)
+            except Exception:
+                resolved = None
+            # Opaque platform-native ids (e.g. photon space GUIDs like
+            # 'any;-;+1555...') match no parser pattern and no directory
+            # entry — pass them through verbatim; the adapter validates.
+            chat_id = resolved or target_ref
+
+    try:
+        from gateway.config import Platform, load_gateway_config
+        platform = Platform(platform_name)
+    except (ValueError, KeyError):
+        return tool_error(f"Unknown platform: {platform_name}")
+
+    if not chat_id:
+        try:
+            config = load_gateway_config()
+            home = config.get_home_channel(platform)
+        except Exception:
+            home = None
+        if not home:
+            return tool_error(
+                f"No chat specified and no home channel set for {platform_name}. "
+                f"Use '{platform_name}:chat_id'."
+            )
+        chat_id = home.chat_id
+
+    runner = None
+    try:
+        from gateway.run import _gateway_runner_ref
+        runner = _gateway_runner_ref()
+    except Exception:
+        runner = None
+    adapter = runner.adapters.get(platform) if runner is not None else None
+    if adapter is None:
+        return tool_error(
+            f"Reactions require a live {platform_name} adapter in the running "
+            "gateway (not available from cron/standalone contexts)."
+        )
+    react_fn = getattr(adapter, "add_reaction", None)
+    if not callable(react_fn):
+        return tool_error(
+            f"Platform '{platform_name}' does not support message reactions."
+        )
+
+    try:
+        from model_tools import _run_async
+        result = _run_async(
+            react_fn(chat_id=chat_id, emoji=emoji, message_id=message_id)
+        )
+    except Exception as e:
+        return json.dumps(_error(f"Reaction failed: {e}"))
+    if isinstance(result, dict):
+        return json.dumps(result)
+    return json.dumps({"success": bool(result)})
+
+
 def _handle_send(args):
     """Send a message to a platform target."""
     target = args.get("target", "")