Keep tool pairs and fold reminders into the last result

Why: Old tool results were filling the window, compaction could split a tool group or commit a stale summary, and reminders arrived as extra user messages.
Evidence: Compaction retries a conflict and opens the circuit after three failures; clearing keeps the last five tool results; a stale file write is rejected; RPC reports started, queued, or handled.
Impact: Requests over the context window replace older tool results with a placeholder. Rewriting an existing file now requires a read in the same run. Subagent text over 32000 characters is capped.
Refs: feature/context-engineering
Co-authored-by: Cursor <cursoragent@cursor.com>

adapters/native/backend.go

@@ -14,6 +14,7 @@ import (
 
 	"agent-native/exec"
 	"agent-native/runtime"
+	"agent-native/runtime/filestate"
 	"agent-native/runtime/llm"
 	"agent-native/runtime/mcp"
 	"agent-native/runtime/promptx"
@@ -171,7 +172,7 @@ func (b *Backend) Execute(ctx context.Context, req exec.Request) (*exec.Result,
 
 	var reg *tools.Registry
 	if profile == exec.ToolProfileWorkspace {
-		reg = tools.WorkspaceTools(workDir)
+		reg = tools.WorkspaceToolsTracked(workDir, filestate.New())
 		skills.RegisterLoader(reg, skillStore)
 		if b.opts.Search != nil {
 			tools.RegisterSearch(reg, b.opts.Search)