Enhance Makefile and README for improved validation and cache management

- Updated the Makefile to include a new `clean-disk` target for removing disk cache, and modified the `run-validation` target to clean the disk cache before starting.
- Enhanced the `check-review-labels` target to include additional file types in the search for temporary review labels, improving code hygiene checks.
- Refined the README.md to clarify the hardening section and improve the description of the `prefill` command.
- Removed the obsolete `test_cache/.gitkeep` file to clean up the repository.

Makefile

@@ -18,7 +18,7 @@ lint: deps check-review-labels ## Run golangci-lint + review label hygiene check
 	@golangci-lint run ./...
 
 check-review-labels: ## Fail if temporary review labels (P0-01, T1, I3, R2, etc.) are found in source
-	@! grep -rnE '\b[A-Z][0-9][^a-zA-Z]' --include='*.go' . 2>/dev/null | grep -v 'G[0-9]\{3\}' || (echo "Error: Found temporary review labels (P*, T*, I*, etc.) in source. See AGENTS.md for the rule." && exit 1)
+	@! grep -rnE '\b[A-Z][0-9][^a-zA-Z]' --include='*.go' --include='*.md' --include='*.yaml' --include='*.sh' --exclude='AGENTS.md' . 2>/dev/null | grep -v 'G[0-9]\{3\}' || (echo "Error: Found temporary review labels (P*, T*, I*, etc.) in source. See AGENTS.md for the rule." && exit 1)
 
 deps: ## Download dependencies
 	@go mod tidy
@@ -26,6 +26,9 @@ deps: ## Download dependencies
 clean: ## Remove build artifacts and test cache
 	@rm -rf bin/ dist/ *.test coverage.out steamcache2
 
+clean-disk: ## Remove disk cache
+	@rm -rf validate-disk/
+
 bench: deps ## Run all benchmarks (MemoryFS + DiskFS variants, including all eviction strategies)
 	@echo "Running MemoryFS benchmarks..."
 	@go test -bench=. -benchmem -run=^$ -benchtime=1s ./vfs/memory
@@ -38,7 +41,7 @@ setcap: build ## Explicitly set cap_net_bind_service on the (just-built) binary
 	@sudo setcap 'cap_net_bind_service=+ep' dist/default_linux_amd64_v1/steamcache2
 	@echo "Done. You should now be able to run 'make run-validation' as your normal user (no root)."
 
-validate run-validation: build ## Start steamcache2 on :80 with small test caches (foreground)
+validate run-validation: build clean-disk ## Start steamcache2 on :80 with small test caches (foreground)
 	@echo "=== Starting steamcache2 in validation mode ==="
 	@echo "Port 80 + small memory/disk caches (for exercising disk tier, GC, etc.)"
 	@echo "Press Ctrl-C to stop the server."
@@ -67,9 +70,6 @@ validate-check: ## Quick post-benchmark sanity check against a running steamcach
 	echo ""; \
 	echo "Tip: also inspect recent server logs for errors, coalesced hits, and disk activity."
 
-prefill: ## Download latest SteamPrefill into bin/steam-prefill/SteamPrefill (gitignored)
-	@./scripts/download-prefill.sh
-
 validate-kill: ## Kill leftover steamcache2 processes (safer, checks process name)
 	@echo "Looking for steamcache2 processes on common validation ports (80 is primary)..."
 	@for port in 80 8040 8080; do \
@@ -95,6 +95,11 @@ validate-kill: ## Kill leftover steamcache2 processes (safer, checks process nam
 	done
 	@echo "Validation server cleanup complete."
 
+prefill: ## Download latest SteamPrefill into bin/steam-prefill/SteamPrefill (gitignored)
+	@./scripts/download-prefill.sh
+
+
+
 
 
 help: ## Show this help message
@@ -109,9 +114,10 @@ help: ## Show this help message
 	@echo "  check-review-labels  Fail on temporary review labels (P*, T*, I*, R*, etc.)"
 	@echo "  deps               Download dependencies"
 	@echo "  clean              Remove build/test artifacts"
+	@echo "  clean-disk         Remove disk cache"
 	@echo "  bench              Run low-level VFS microbenchmarks"
-	@echo "  validate / run-validation  Start server on :80 (builds, auto-setcaps fresh binary, then runs as normal user)"
+	@echo "  validate / run-validation  Start server on :80 (builds, auto-setcaps fresh binary, then runs as normal user, cleans disk cache first)"
 	@echo "  setcap               Explicitly set cap on current build (for port 80 use outside validate)"
 	@echo "  validate-check     Quick /metrics report after running a workload"
 	@echo "  validate-kill      Kill leftover steamcache2 processes (safer)"
-	@echo "  prefill            Download latest SteamPrefill into bin/steam-prefill/ (for use with run-validation)"
+	@echo "  prefill            Download latest SteamPrefill into bin/steam-prefill/SteamPrefill (gitignored)"