feat: add swarm-common obsidian vault

Add Obsidian vault to the swarm-common virtiofs share for access
from zap VM and other VMs. Contains agent memory, notes, and
infrastructure documentation.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

swarm-common/obsidian-vault/zap/memory/references/anthropic-prompt-caching.md

@@ -0,0 +1,72 @@
+# Anthropic — Prompt Caching Best Practices
+
+**Source**: https://docs.anthropic.com/en/docs/build-with-claude/prompt-caching
+**Fetched**: 2026-03-05
+
+---
+
+## How It Works
+
+1. On first request: system processes full prompt and caches the prefix once the response begins.
+2. On subsequent requests with same prefix: uses cached version (much cheaper + faster).
+3. Cache is checked against a cryptographic hash of the prefix content.
+
+## Two Caching Modes
+
+### Automatic Caching (recommended for multi-turn)
+Add `cache_control: {"type": "ephemeral"}` at the **top level** of the request body.
+- System automatically caches all content up to the last cacheable block.
+- Moves cache breakpoint forward as conversation grows.
+- Best for multi-turn conversations.
+
+### Explicit Cache Breakpoints
+Place `cache_control` directly on individual content blocks.
+- Finer control over exactly what gets cached.
+- Use when you want to cache specific blocks (e.g., a large document) but not others.
+
+## Cache Lifetimes
+
+| Duration | Cost | Availability |
+|----------|------|-------------|
+| 5 minutes (default) | 1.25x base input price for write | All models |
+| 1 hour | 2x base input price for write | Available at additional cost |
+
+- Cache **reads** cost 0.1x (10%) of base input price.
+- Cache is refreshed for **no additional cost** each time cached content is used.
+- Default TTL: **5 minutes** (refreshed on each use within TTL).
+
+## Pricing Per Million Tokens (relevant models)
+
+| Model | Base Input | 5m Write | 1h Write | Cache Read | Output |
+|-------|-----------|----------|----------|------------|--------|
+| Claude Opus 4.6 | $5 | $6.25 | $10 | $0.50 | $25 |
+| Claude Sonnet 4.6 | $3 | $3.75 | $6 | $0.30 | $15 |
+| Claude Haiku 4.5 | $1 | $1.25 | $2 | $0.10 | $5 |
+
+> Note: We use Copilot subscription (flat rate), so per-token cost doesn't apply directly. But quota burn follows similar relative proportions — caching still saves quota by reducing re-processing of identical prefixes.
+
+## Supported Models
+- Claude Opus 4.6, 4.5, 4.1, 4
+- Claude Sonnet 4.6, 4.5, 4
+- Claude Haiku 4.5, 3.5
+
+**Not supported**: Non-Claude models (GPT, GLM, Gemini) — caching is Anthropic-only.
+
+## What Gets Cached
+Prefix order: `tools` → `system` → `messages` (up to the cache breakpoint).
+
+The full prefix is cached — all of tools, system, and messages up to and including the marked block.
+
+## Key Best Practices
+
+1. **Put static content first**: Instructions, system prompts, and background context should come before dynamic/user content.
+2. **Use 1-hour cache for long sessions**: Default 5-minute TTL means cache expires between turns if idle > 5 min. Use 1h for agents with longer gaps.
+3. **Automatic caching for multi-turn**: Simplest approach, handles the growing message history automatically.
+4. **Minimum size**: Cache only activates for content > a certain token threshold (details not specified, but system prompts qualify easily).
+5. **Privacy**: Cache stores KV representations and cryptographic hashes, NOT raw text. ZDR-compatible.
+
+## For Our Setup (OpenClaw)
+- Main session system prompt is large (~15-20k tokens) and mostly static → ideal caching candidate.
+- Heartbeat turns are the same every 25-30min → if using 1h cache, heartbeats keep cache warm for free.
+- OpenClaw's `cacheRetention` config likely maps to this `cache_control` setting.
+- Applies to: `litellm/copilot-claude-*` models only. Does NOT apply to GLM, GPT-4o, Gemini.