Add configuration options and enable dynamic memory management through cc-backend callback

CLAUDE.md

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+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Project Overview
+
+cc-metric-store is an in-memory time-series database for HPC cluster metrics, part of the ClusterCockpit monitoring suite. Data is indexed by a hierarchical tree (cluster → host → socket/cpu/gpu) and accessed via selectors. The core storage engine lives in `cc-backend/pkg/metricstore`; this repo provides the HTTP API wrapper.
+
+## Build Commands
+
+```bash
+make                 # Build binary, copy config template, create checkpoint dirs
+make clean           # Clean build cache and binary
+make distclean       # Also remove ./var and config.json
+make swagger         # Regenerate Swagger from source comments
+make test            # Run go build, go vet, go test
+```
+
+## Testing
+
+```bash
+go test -v ./...              # Run tests
+go test -bench=. -race -v ./...  # With benchmarks and race detector
+```
+
+Integration test scripts in `/endpoint-test-scripts/` for manual API testing.
+
+## Running
+
+```bash
+./cc-metric-store                           # Uses ./config.json
+./cc-metric-store -config /path/to/config.json
+./cc-metric-store -dev                      # Enable Swagger UI at /swagger/
+./cc-metric-store -loglevel debug           # debug|info|warn|err|crit
+```
+
+## Architecture
+
+**Entry point:** `cmd/cc-metric-store/main.go`
+- `run()` → parse flags, init logging/config, connect NATS
+- `runServer()` → init metricstore from cc-backend, start HTTP server
+
+**Key packages:**
+- `internal/api/` - REST endpoints (query, write, free, debug, healthcheck) and JWT auth (Ed25519)
+- `internal/config/` - Config loading and JSON schema validation
+- External: `cc-backend/pkg/metricstore` - actual time-series storage engine
+
+**API endpoints** (all support optional JWT auth):
+- `GET /api/query/` - Query metrics with selectors
+- `POST /api/write/` - Write metrics (InfluxDB line protocol)
+- `POST /api/free/` - Free buffers up to timestamp
+- `GET /api/debug/` - Dump internal state
+- `GET /api/healthcheck/` - Node health status
+
+## Selectors
+
+Data is accessed via hierarchical selectors:
+```
+["cluster1", "host1", "cpu0"]           # Specific CPU
+["cluster1", "host1", ["cpu4", "cpu5"]] # Multiple CPUs
+["cluster1", "host1"]                   # Entire node (all CPUs implied)
+```
+
+## Configuration
+
+Config file structure (see `configs/config.json`):
+- `main` - Server address, TLS certs, JWT public key, user/group for privilege drop
+- `metrics` - Per-metric frequency and aggregation strategy (sum/avg/null)
+- `metric-store` - Checkpoints, memory cap, retention, cleanup mode, NATS subscriptions
+- `nats` - Optional NATS connection for receiving metrics
+
+## Test JWT
+
+For testing with JWT auth enabled:
+```
+eyJ0eXAiOiJKV1QiLCJhbGciOiJFZERTQSJ9.eyJ1c2VyIjoiYWRtaW4iLCJyb2xlcyI6WyJST0xFX0FETUlOIiwiUk9MRV9BTkFMWVNUIiwiUk9MRV9VU0VSIl19.d-3_3FZTsadPjDEdsWrrQ7nS0edMAR4zjl-eK7rJU3HziNBfI9PDHDIpJVHTNN5E5SlLGLFXctWyKAkwhXL-Dw
+```