feat(spec): support tool aliases (#107)

closes #57

IRIS now automatically read and suggest internal configuration aliases
for Git (`.gitconfig`, `.git/config`) and Cargo (`.cargo/config.toml`)

- Added the `Provider` interface and extended registry for CLI tools
that define aliases
- Git: parse aliases via `git config --show-scope`, supporting raw
tab/space separation and scope differentiation
- Cargo: traverse the directory tree upwards to root to read the
`.cargo/config.toml` configuration
- 0ms hot-path caching: key caching is calculated entirely via `os.Stat`
mtime (no subprocess spawn) combined with a 2-second TTL window to
ensure 0ms latency when typing
- Lookup integration: display alias suggestions at the subcommand level
and automatically expand aliases as the user enters further arguments
(ignore shell pipeline commands starting with `!`)

spec/alias/git_provider.go

@@ -0,0 +1,166 @@
+package alias
+
+import (
+	"bytes"
+	"context"
+	"fmt"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"strings"
+	"sync"
+	"time"
+)
+
+type GitProvider struct {
+	cacheKey  string
+	cached    []AliasEntry
+	lastCheck time.Time
+	mu        sync.Mutex
+}
+
+func (p *GitProvider) ToolName() string {
+	return "git"
+}
+
+func (p *GitProvider) GetAliases(cwd string) []AliasEntry {
+	p.mu.Lock()
+	defer p.mu.Unlock()
+
+	now := time.Now()
+	if p.cached != nil && now.Sub(p.lastCheck) < 2*time.Second {
+		return p.cached
+	}
+
+	key := p.buildCacheKey(cwd)
+	p.lastCheck = now
+
+	if p.cacheKey != "" && p.cacheKey == key {
+		return p.cached
+	}
+
+	p.cached = p.parse(cwd)
+	p.cacheKey = key
+	return p.cached
+}
+
+func (p *GitProvider) buildCacheKey(cwd string) string {
+	var sb strings.Builder
+	sb.WriteString(cwd)
+
+	// Check local config via fast os.Stat traversal
+	if configPath := resolveGitConfigPath(cwd); configPath != "" {
+		if info, err := os.Stat(configPath); err == nil {
+			fmt.Fprintf(&sb, "|local:%s", info.ModTime().String())
+		}
+	}
+
+	// Check global config
+	if home, err := os.UserHomeDir(); err == nil {
+		globalConfig := filepath.Join(home, ".gitconfig")
+		if info, err := os.Stat(globalConfig); err == nil {
+			fmt.Fprintf(&sb, "|global:%s", info.ModTime().String())
+		}
+	}
+
+	return sb.String()
+}
+
+func resolveGitConfigPath(cwd string) string {
+	dir := cwd
+	for dir != "" {
+		gitPath := filepath.Join(dir, ".git")
+		info, err := os.Stat(gitPath)
+		if err == nil {
+			if info.IsDir() {
+				return filepath.Join(gitPath, "config")
+			}
+			content, errRead := os.ReadFile(gitPath)
+			if errRead == nil {
+				s := strings.TrimSpace(string(content))
+				if after, ok := strings.CutPrefix(s, "gitdir: "); ok {
+					gitDir := strings.TrimSpace(after)
+					if !filepath.IsAbs(gitDir) {
+						gitDir = filepath.Join(dir, gitDir)
+					}
+					return filepath.Join(gitDir, "config")
+				}
+			}
+			return filepath.Join(dir, ".git", "config")
+		}
+		parent := filepath.Dir(dir)
+		if parent == dir {
+			break
+		}
+		dir = parent
+	}
+	return ""
+}
+
+func (p *GitProvider) parse(cwd string) []AliasEntry {
+	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
+	defer cancel()
+
+	// Try with --show-scope first
+	cmd := exec.CommandContext(ctx, "git", "config", "--get-regexp", "--show-scope", "^alias\\.")
+	cmd.Dir = cwd
+	out, err := cmd.Output()
+	hasScope := true
+	if err != nil {
+		ctx2, cancel2 := context.WithTimeout(context.Background(), 2*time.Second)
+		defer cancel2()
+		// Fallback for older git
+		cmd = exec.CommandContext(ctx2, "git", "config", "--get-regexp", "^alias\\.")
+		cmd.Dir = cwd
+		out, err = cmd.Output()
+		hasScope = false
+		if err != nil {
+			return nil
+		}
+	}
+	return p.parseOutput(out, hasScope)
+}
+
+func (p *GitProvider) parseOutput(out []byte, hasScope bool) []AliasEntry {
+	var entries []AliasEntry
+	lines := strings.Split(string(bytes.TrimSpace(out)), "\n")
+	for _, line := range lines {
+		line = strings.TrimSpace(line)
+		if line == "" {
+			continue
+		}
+
+		if hasScope {
+			idx := strings.IndexAny(line, " \t")
+			if idx == -1 {
+				continue
+			}
+			scope := line[:idx]
+			rest := strings.TrimSpace(line[idx:])
+			parts := strings.SplitN(rest, " ", 2)
+			if len(parts) == 2 {
+				name := strings.TrimPrefix(parts[0], "alias.")
+				entries = append(entries, AliasEntry{
+					Name:      name,
+					Expansion: parts[1],
+					Scope:     scope,
+				})
+			}
+		} else {
+			parts := strings.SplitN(line, " ", 2)
+			if len(parts) == 2 {
+				name := strings.TrimPrefix(parts[0], "alias.")
+				entries = append(entries, AliasEntry{
+					Name:      name,
+					Expansion: parts[1],
+					Scope:     "",
+				})
+			}
+		}
+	}
+	return entries
+}
+
+func init() {
+	Register(&GitProvider{})
+}