[WIP] feat: Cache-aware context pruning (role-based)

[quangdang46]

Gap #22 — Medium

Cache-aware context pruning with role-based budgeting and agent-output blacklisting.

Source: codebuff

What's needed:

• Cache-aware pruning (>5 min gap triggers re-pruning)
• Role-based budgeting (20K for assistant/tool, 50K for user content)
• Agent-output blacklisting (don't summarize file-picker, basher output)
• Token budget enforcement per role
• Prompt cache expiry detection

Reference: codebuff agents/context-pruner.ts

Note: jcode has DCP (PR #339) for basic context pruning. This adds cache-aware and role-based sophistication.