Parse Pi transcripts during attach and explain

[entire]

https://entire.io/gh/entireio/cli/trails/944

This draft pull request was opened by Entire after CI was requested for the linked trail. Feel free to edit the title or body — the link above is what keeps the trail and PR connected.

[Copilot]

Pull request overview

This PR adds first-class handling for Pi’s native v3 JSONL transcripts so attach and explain can extract/format prompts and models correctly, and summarization can condense Pi sessions the same way other agents are handled.

Changes:

• Extend transcript condensation to support agent.AgentTypePi, including native Pi JSONL → compact → condensed entries.
• Improve attach metadata extraction by deferring to agent-native prompt/model extractors when available.
• Add unit tests covering Pi native transcript parsing for summarization, explain formatting, and attach metadata extraction.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
cmd/entire/cli/summarize/summarize.go	Adds Pi-specific condensed-transcript builder and routes Pi agent type to it.
cmd/entire/cli/summarize/summarize_test.go	Adds summarization coverage for native Pi JSONL and parallelizes an existing compact fallback test.
cmd/entire/cli/explain_test.go	Adds coverage that explain formatting no longer fails on native Pi JSONL.
cmd/entire/cli/attach.go	Switches attach transcript metadata extraction to an agent-aware extraction path.
cmd/entire/cli/attach_transcript.go	Introduces agent-aware metadata extraction using prompt/model extractor capabilities.
cmd/entire/cli/attach_test.go	Adds coverage ensuring Pi-native prompt/model metadata is extracted during attach.