### New Features
- Runtime tool registration now applies immediately in active sessions. Tools registered via `pi.registerTool()` after startup are available to `pi.getAllTools()` and the LLM without `/reload` ([docs/extensions.md](docs/extensions.md), [examples/extensions/dynamic-tools.ts](examples/extensions/dynamic-tools.ts), [#1720](https://github.com/badlogic/pi-mono/issues/1720)).
- Tool definitions can customize the default system prompt with `promptSnippet` (`Available tools`) and `promptGuidelines` (`Guidelines`) while the tool is active ([docs/extensions.md](docs/extensions.md), [#1720](https://github.com/badlogic/pi-mono/issues/1720)).
- Custom tool renderers can suppress transcript output without leaving extra spacing or empty transcript footprint in interactive rendering ([docs/extensions.md](docs/extensions.md), [#1719](https://github.com/badlogic/pi-mono/pull/1719)).
### Added
- Added optional `promptSnippet` to `ToolDefinition` for one-line entries in the default system prompt's `Available tools` section. Active extension tools appear there when registered and active ([#1237](https://github.com/badlogic/pi-mono/pull/1237) by [@semtexzv](https://github.com/semtexzv)).
- Added optional `promptGuidelines` to `ToolDefinition` so active tools can append tool-specific bullets to the default system prompt `Guidelines` section ([#1720](https://github.com/badlogic/pi-mono/issues/1720)).
### Fixed
- Fixed `pi.registerTool()` dynamic registration after session initialization. Tools registered in `session_start` and later handlers now refresh immediately, become active, and are visible to the LLM without `/reload` ([#1720](https://github.com/badlogic/pi-mono/issues/1720))
- Fixed session message persistence ordering by serializing `AgentSession` event processing, preventing `toolResult` entries from being written before their corresponding assistant tool-call messages when extension handlers are asynchronous ([#1717](https://github.com/badlogic/pi-mono/issues/1717))
- Fixed spacing artifacts when custom tool renderers intentionally suppress per-call transcript output, including extra blank rows in interactive streaming and non-zero transcript footprint for empty custom renders ([#1719](https://github.com/badlogic/pi-mono/pull/1719) by [@alasano](https://github.com/alasano))
- Fixed `session.prompt()` returning before retry completion by creating the retry promise synchronously at `agent_end` dispatch, which closes a race when earlier queued event handlers are async ([#1726](https://github.com/badlogic/pi-mono/pull/1726) by [@pasky](https://github.com/pasky))