Workflow: provider-aware context policy and same-session compaction

[Relaxe111]

Goal

Paseo should let an orchestrator manage context for each agent without creating a new session.

There are two separate features:

1. Set a context limit when the agent starts.
2. Compact the existing session.

A provider may support one, both, or neither.

Provider support

Provider	Set token limit	Compact same session
Codex	Yes	Yes
Claude	Yes	Not through its SDK
OpenCode	No exact limit	Yes
Pi / OMP	No exact limit	Yes
Cursor / ACP	No	No

Proposed change

• Provider information reports the two capabilities separately.
• Agent creation accepts the native Codex or Claude context setting.
• A new agent.compact API compacts only the existing session.
• It returns confirmed only after Paseo sees completion and proves the native session ID did not change.
• Unsupported providers return unsupported. Paseo does not fake support.

This adds no Paseo context classes, global settings, compact prompt messages, reloads, or replacement sessions.

Proof

• 911 focused tests passed.
• Live Codex, Claude, and OpenCode checks kept the same native session IDs.
• Codex usage changed from 31,474 to 29,373 tokens after native compaction.
• Cursor remains unsupported.

Draft implementation: #3739
Related transport work: #3077

Questions

Does this design fit Paseo? Are the capability and API names clear?