Add go-llm v2: redesigned API for simpler LLM abstraction

v2 is a new Go module (v2/) with a dramatically simpler API:
- Unified Message type (no more Input marker interface)
- Define[T] for ergonomic tool creation with standard context.Context
- Chat session with automatic tool-call loop (agent loop)
- Streaming via pull-based StreamReader
- MCP one-call connect (MCPStdioServer, MCPHTTPServer, MCPSSEServer)
- Middleware support (logging, retry, timeout, usage tracking)
- Decoupled JSON Schema (map[string]any, no provider coupling)
- Sample tools: WebSearch, Browser, Exec, ReadFile, WriteFile, HTTP
- Providers: OpenAI, Anthropic, Google (all with streaming)

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

v2/tools/readfile.go

@@ -0,0 +1,81 @@
+package tools
+
+import (
+	"bufio"
+	"context"
+	"fmt"
+	"os"
+	"strings"
+
+	llm "gitea.stevedudenhoeffer.com/steve/go-llm/v2"
+)
+
+// ReadFileParams defines parameters for the read file tool.
+type ReadFileParams struct {
+	Path  string `json:"path" description:"File path to read"`
+	Start *int   `json:"start,omitempty" description:"Starting line number (1-based, inclusive)"`
+	End   *int   `json:"end,omitempty" description:"Ending line number (1-based, inclusive)"`
+}
+
+// ReadFile creates a file reading tool.
+//
+// Example:
+//
+//	tools := llm.NewToolBox(tools.ReadFile())
+func ReadFile() llm.Tool {
+	return llm.Define[ReadFileParams]("read_file", "Read the contents of a file",
+		func(ctx context.Context, p ReadFileParams) (string, error) {
+			f, err := os.Open(p.Path)
+			if err != nil {
+				return "", fmt.Errorf("opening file: %w", err)
+			}
+			defer f.Close()
+
+			// If no line range specified, read the whole file (limited to 1MB)
+			if p.Start == nil && p.End == nil {
+				info, err := f.Stat()
+				if err != nil {
+					return "", fmt.Errorf("stat file: %w", err)
+				}
+				if info.Size() > 1<<20 {
+					return "", fmt.Errorf("file too large (%d bytes), use start/end to read a range", info.Size())
+				}
+				data, err := os.ReadFile(p.Path)
+				if err != nil {
+					return "", fmt.Errorf("reading file: %w", err)
+				}
+				return string(data), nil
+			}
+
+			// Read specific line range
+			start := 1
+			end := -1
+			if p.Start != nil {
+				start = *p.Start
+			}
+			if p.End != nil {
+				end = *p.End
+			}
+
+			var lines []string
+			scanner := bufio.NewScanner(f)
+			lineNum := 0
+			for scanner.Scan() {
+				lineNum++
+				if lineNum < start {
+					continue
+				}
+				if end > 0 && lineNum > end {
+					break
+				}
+				lines = append(lines, fmt.Sprintf("%d: %s", lineNum, scanner.Text()))
+			}
+
+			if err := scanner.Err(); err != nil {
+				return "", fmt.Errorf("scanning file: %w", err)
+			}
+
+			return strings.Join(lines, "\n"), nil
+		},
+	)
+}