filter hooks by connection and context in core

docs/plugin-api-additions/filters.md

@@ -0,0 +1,24 @@
+# Core-filtered hooks
+
+Python: `hook_server_filtered(name, callback, userdata=None, priority=PRI_NORM,
+connection_id=None, channel=None)` and `hook_print_filtered(...)`.
+Callbacks match the existing attrs variants: `(word, word_eol, userdata, attrs)`.
+The connection ID distinguishes duplicate names; None/-1 means any connection
+(including connection ID zero). A channel restriction uses that connection's
+IRC comparator. None means any context; an empty string is an exact restriction.
+
+C: the corresponding zoitechat_hook_*_filtered functions accept
+`(ph, name, pri, flags, connection_id, channel, callback, userdata)`;
+flags=0, ID=-1 for any and NULL channel for any. Check
+`get_info("api_context_filters")` for "1" before accessing the new Windows slots.
+
+Filtering takes place before Python/interpreter entry. Existing unrestricted
+hooks, priority, EAT semantics and unload/unhook handling are unchanged.
+Filters refer to the core-selected context, not an IRC target parsed from the
+line: unknown queries/channels can still have a server-tab context, and QUIT
+has its usual single server-hook context. Connection IDs last only this process.
+
+```python
+zoitechat.hook_print_filtered('Channel Message', callback,
+                             connection_id=zoitechat.get_prefs('id'), channel='#zoitechat')
+```