fix(FN-2392): normalize skill-facing tool references to fn_*

- Update Fusion skill docs, prompts, and capability references to use public fn_* tool names consistently
- Align engine system prompts and tool schemas for messaging/task actions with fn_send_message, fn_read_messages, fn_task_* naming
- Refresh related tests across CLI, engine, dashboard, and core to match normalized tool naming and behavior
- Add a patch changeset for @runfusion/fusion describing the skill-tool namespace normalization

packages/cli/skill/fusion/references/extension-tools.md

@@ -2,6 +2,8 @@
 
 All tools are registered via the pi extension. They are available in any pi agent session when the Fusion extension is installed.
 
+> Naming contract: all externally exposed Fusion extension tools are `fn_*` (for example `fn_task_create`). Internal engine/executor runtime tools (`task_create`, `task_update`, `task_log`, `task_done`, etc.) are separate and intentionally out of scope for this skill surface.
+
 ## Task Tools
 
 ### fn_task_create

packages/cli/skill/fusion/references/fusion-capabilities.md

@@ -7,6 +7,8 @@ Triage → Todo → In Progress → In Review → Done → Archived
 
 ## Pi Extension Tools (Available to Agents)
 
+All skill/extension tool invocations in this catalog use the public `fn_*` namespace. Engine runtime tools (for example `task_create`, `task_update`, `task_log`, `task_done`) are internal and intentionally not listed here.
+
 | Tool | Purpose |
 |------|---------|
 | `fn_task_create` | Create a new task in triage |