KV Cache Phase 1: make skills, prompts, extensions, and plugin tools deterministic

[shuyhere]

Summary

Make prompt assembly inputs deterministic by sorting discovered skills, prompts, extension files, and plugin tools before rendering or request construction.

Why

Prompt/KV cache reuse depends on exact repeated prefixes, not semantic similarity. Today, filesystem discovery and plugin registration order can drift across runs, which can mutate:

• the <available_skills> section,
• prompt template listings,
• extension load order,
• plugin tool order,
• final tool definitions sent to providers.

This is a direct cache-breaker.

Scope

Introduce deterministic ordering rules for all semi-static prompt resources.

Required ordering rules

• extension files sorted by normalized path
• skills sorted by (name, path)
• prompts sorted by (name, path)
• plugin tools sorted by (source path, tool name)
• final tool definitions rendered in a stable order

Code touchpoints

• crates/cli/src/extensions/discovery.rs
• crates/cli/src/extensions.rs
• crates/cli/src/session_bootstrap.rs
• crates/cli/src/run.rs
• plugin runtime assembly code

Acceptance criteria

• repeated bootstrap in the same repo/settings yields identical skill/prompt rendering
• plugin tool order is stable across runs
• stable prefix hash does not change because of filesystem enumeration order
• tests cover ordering stability

Reference

• knowledge/internal/KV_CACHE_REFACTOR_MASTER_PLAN.md