Summarize the conversation without tool output on request - #587

The change adds two builder options to ModelSummarizer (tool rendering mode and an output-token cap) and two prompt sections; neither introduces a security-relevant sink. Rendering is delegated to render_message_for_summary_with, which for Markers mode shortens tool arguments and drops tool results, and max_tokens is set from a caller-supplied configuration field, not untrusted input. Tests exercise the new behaviour directly; no defect found. _The code index is behind this pull request (indexed at `13a38cd9a17e`), so retrieved context may be out of date._

No findings.