Initial implementation of compaction MCP server

Ephemeral, per-session context management for LLMs with 8 MCP tools:
store, query, status, compact, pin, forget, configure, update.

Features: scoring with decay/importance/access, Jaccard dedup,
summary promotion, budget-based eviction, auto-detection of
client context window via MCP hooks.

main.go

@@ -0,0 +1,70 @@
+package main
+
+import (
+	"context"
+	"flag"
+	"fmt"
+	"os"
+	"strings"
+
+	"github.com/mark3labs/mcp-go/mcp"
+	"github.com/mark3labs/mcp-go/server"
+)
+
+const serverInstructions = `Context compactor — manages working memory within a token budget.
+
+At session start, call 'configure' with token_budget set to ~40% of your context window.
+Example: 200K context window → token_budget = 80000.
+
+Workflow:
+- 'store' important context (always include a summary for efficient compaction)
+- 'query' to retrieve stored information instead of re-reading sources
+- 'status' to check budget usage
+- 'compact' when usage is high — it frees space and identifies items needing summarization
+- 'update' to add summaries to items flagged by compaction`
+
+func main() {
+	budget := flag.Int("budget", 100000, "Token budget for context storage")
+	flag.Parse()
+
+	budgetExplicit := false
+	flag.Visit(func(f *flag.Flag) {
+		if f.Name == "budget" {
+			budgetExplicit = true
+		}
+	})
+
+	store := NewStore(*budget)
+
+	hooks := &server.Hooks{}
+	if !budgetExplicit {
+		hooks.OnAfterInitialize = append(hooks.OnAfterInitialize,
+			func(ctx context.Context, id any, req *mcp.InitializeRequest, res *mcp.InitializeResult) {
+				name := strings.ToLower(req.Params.ClientInfo.Name)
+				switch {
+				case strings.Contains(name, "claude"):
+					// Claude models: 200K context → 40% = 80K budget
+					store.Configure(80000, nil, 0)
+				case strings.Contains(name, "cursor"):
+					store.Configure(60000, nil, 0)
+				}
+			},
+		)
+	}
+
+	s := server.NewMCPServer(
+		"compactor",
+		"0.1.0",
+		server.WithToolCapabilities(false),
+		server.WithRecovery(),
+		server.WithInstructions(serverInstructions),
+		server.WithHooks(hooks),
+	)
+
+	registerTools(s, store)
+
+	if err := server.ServeStdio(s); err != nil {
+		fmt.Fprintf(os.Stderr, "server error: %v\n", err)
+		os.Exit(1)
+	}
+}