docs(plugins): catalog active deprecations in sdk-migration and cross-link from hooks

docs/plugins/hooks.md

@@ -223,8 +223,30 @@ resources.
 Do not rely on the internal `gateway:startup` hook for plugin-owned runtime
 services.
 
+## Upcoming deprecations
+
+A few hook-adjacent surfaces are deprecated but still supported. Migrate
+before the next major release:
+
+- **Plaintext channel envelopes** in `inbound_claim` and `message_received`
+  handlers. Read `BodyForAgent` and the structured user-context blocks
+  instead of parsing flat envelope text. See
+  [Plaintext channel envelopes → BodyForAgent](/plugins/sdk-migration#active-deprecations).
+- **`before_agent_start`** remains for compatibility. New plugins should use
+  `before_model_resolve` and `before_prompt_build` instead of the combined
+  phase.
+- **`onResolution` in `before_tool_call`** now uses the typed
+  `PluginApprovalResolution` union (`allow-once` / `allow-always` / `deny` /
+  `timeout` / `cancelled`) instead of a free-form `string`.
+
+For the full list — memory capability registration, provider thinking
+profile, external auth providers, provider discovery types, task runtime
+accessors, and the `command-auth` → `command-status` rename — see
+[Plugin SDK migration → Active deprecations](/plugins/sdk-migration#active-deprecations).
+
 ## Related
 
+- [Plugin SDK migration](/plugins/sdk-migration) — active deprecations and removal timeline
 - [Building plugins](/plugins/building-plugins)
 - [Plugin SDK overview](/plugins/sdk-overview)
 - [Plugin entry points](/plugins/sdk-entrypoints)