feat(security): security hardening, proxy support, and GL045 HTTP include warning

Security fixes:
- Path traversal guard in include: local: — paths with ../ that escape
  the repo root are rejected instead of reading arbitrary host files
- HTTP timeout (30 s) on all fetcher requests to prevent indefinite hangs
- Response size cap (10 MiB) via io.LimitReader to prevent memory exhaustion
- Cache directory and file permissions tightened to 0700/0600
- LSP Content-Length cap (64 MiB) to guard against DoS from a malicious client

New feature:
- --proxy flag on check, graph, and lsp subcommands; also proxy: key in
  .glint.yml; overrides system HTTP_PROXY / HTTPS_PROXY env vars when set;
  cmdGraph and cmdLSP now also load .glint.yml for proxy/token/url fallbacks

New lint rule:
- GL045 (Warning): include: remote: using plain http:// instead of https://

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

internal/fetcher/cache.go

@@ -26,10 +26,10 @@ func cacheWrite(dir, key string, data []byte) {
 	if dir == "" {
 		return
 	}
-	if err := os.MkdirAll(dir, 0o755); err != nil {
+	if err := os.MkdirAll(dir, 0o700); err != nil {
 		return
 	}
-	_ = os.WriteFile(cachePath(dir, key), data, 0o644)
+	_ = os.WriteFile(cachePath(dir, key), data, 0o600)
 }
 
 // cachePath returns the filesystem path for a cache entry.

internal/fetcher/cache_test.go

@@ -71,3 +71,28 @@ func TestCacheWrite_MkdirAll(t *testing.T) {
 		t.Errorf("directory not created: %v", err)
 	}
 }
+
+func TestCacheWrite_FilePermissions(t *testing.T) {
+	dir := t.TempDir()
+	cacheWrite(dir, "seckey", []byte("secret"))
+	info, err := os.Stat(cachePath(dir, "seckey"))
+	if err != nil {
+		t.Fatalf("stat cache file: %v", err)
+	}
+	if mode := info.Mode().Perm(); mode != 0o600 {
+		t.Errorf("cache file mode = %04o; want 0600", mode)
+	}
+}
+
+func TestCacheWrite_DirPermissions(t *testing.T) {
+	parent := t.TempDir()
+	dir := filepath.Join(parent, "glint-cache")
+	cacheWrite(dir, "k", []byte("v"))
+	info, err := os.Stat(dir)
+	if err != nil {
+		t.Fatalf("stat cache dir: %v", err)
+	}
+	if mode := info.Mode().Perm(); mode != 0o700 {
+		t.Errorf("cache dir mode = %04o; want 0700", mode)
+	}
+}

internal/fetcher/gitlab.go

@@ -8,8 +8,18 @@ import (
 	"net/url"
 	"os"
 	"strings"
+	"time"
 )
 
+// httpClient is the shared HTTP client for all fetcher requests.
+// Timeout guards against hung remote servers. Transport is intentionally nil
+// so http.DefaultTransport is used dynamically — allowing tests to swap it.
+var httpClient = &http.Client{Timeout: 30 * time.Second}
+
+// maxResponseBytes is the per-response size cap. Responses larger than this
+// are rejected to prevent memory exhaustion from pathological servers.
+const maxResponseBytes int64 = 10 << 20 // 10 MiB
+
 // TokenSource describes where a token was found, which determines the correct
 // authentication header to use with the GitLab API.
 type TokenSource int
@@ -27,6 +37,10 @@ type GitLabConfig struct {
 	Source   TokenSource
 	CacheDir string // local cache directory; empty = caching disabled
 	Offline  bool   // when true, return an error instead of making network calls
+	// ProxyURL overrides the HTTP proxy for all requests made with this config.
+	// Empty string means use system proxy settings (HTTP_PROXY / HTTPS_PROXY /
+	// NO_PROXY env vars honoured automatically by http.DefaultTransport).
+	ProxyURL string
 }
 
 // AutoConfig builds a GitLabConfig from environment variables.
@@ -56,6 +70,33 @@ func AutoConfig() GitLabConfig {
 	return cfg
 }
 
+// WithProxy returns a copy of cfg with ProxyURL set.
+func (cfg GitLabConfig) WithProxy(proxyURL string) GitLabConfig {
+	cfg.ProxyURL = proxyURL
+	return cfg
+}
+
+// client returns an HTTP client for this config.
+// When ProxyURL is set it takes precedence over system proxy env vars;
+// otherwise http.DefaultTransport's built-in ProxyFromEnvironment is used.
+func (cfg GitLabConfig) client() *http.Client {
+	if cfg.ProxyURL == "" {
+		return httpClient
+	}
+	proxyURL, err := url.Parse(cfg.ProxyURL)
+	if err != nil {
+		return httpClient
+	}
+	// Clone the default transport so all TLS/dial settings are preserved.
+	t, ok := http.DefaultTransport.(*http.Transport)
+	if !ok {
+		return httpClient
+	}
+	transport := t.Clone()
+	transport.Proxy = http.ProxyURL(proxyURL)
+	return &http.Client{Timeout: httpClient.Timeout, Transport: transport}
+}
+
 // WithOverrides returns a copy of cfg with the provided overrides applied.
 // Non-empty strings overwrite the corresponding field; booleans are always
 // applied (so offline: false explicitly clears offline mode).
@@ -128,16 +169,19 @@ func (cfg GitLabConfig) FetchFile(project, filePath, ref string) ([]byte, error)
 		}
 	}
 
-	resp, err := http.DefaultClient.Do(req)
+	resp, err := cfg.client().Do(req)
 	if err != nil {
 		return nil, fmt.Errorf("GET %s: %w", apiURL, err)
 	}
 	defer resp.Body.Close()
 
-	body, err := io.ReadAll(resp.Body)
+	body, err := io.ReadAll(io.LimitReader(resp.Body, maxResponseBytes+1))
 	if err != nil {
 		return nil, fmt.Errorf("reading response body: %w", err)
 	}
+	if int64(len(body)) > maxResponseBytes {
+		return nil, fmt.Errorf("response body exceeds maximum size (%d MiB)", maxResponseBytes>>20)
+	}
 
 	if resp.StatusCode != http.StatusOK {
 		msg := strings.TrimSpace(string(body))
@@ -169,15 +213,18 @@ func (cfg GitLabConfig) FetchURL(rawURL string) ([]byte, error) {
 		return nil, fmt.Errorf("offline mode: %s is not in the local cache (run without --offline first to populate the cache)", rawURL)
 	}
 
-	resp, err := http.Get(rawURL) //nolint:noctx
+	resp, err := cfg.client().Get(rawURL)
 	if err != nil {
 		return nil, fmt.Errorf("GET %s: %w", rawURL, err)
 	}
 	defer resp.Body.Close()
-	body, err := io.ReadAll(resp.Body)
+	body, err := io.ReadAll(io.LimitReader(resp.Body, maxResponseBytes+1))
 	if err != nil {
 		return nil, fmt.Errorf("reading body: %w", err)
 	}
+	if int64(len(body)) > maxResponseBytes {
+		return nil, fmt.Errorf("response body exceeds maximum size (%d MiB)", maxResponseBytes>>20)
+	}
 	if resp.StatusCode != http.StatusOK {
 		return nil, fmt.Errorf("GET %s: status %d", rawURL, resp.StatusCode)
 	}

internal/fetcher/gitlab_test.go

@@ -6,6 +6,7 @@ import (
 	"net/http"
 	"net/http/httptest"
 	"os"
+	"strings"
 	"testing"
 )
 
@@ -339,3 +340,46 @@ func TestFetchURL_NotOK(t *testing.T) {
 	_, err := cfg.FetchURL(srv.URL)
 	if err == nil { t.Fatal("expected error for non-200 status") }
 }
+
+func TestFetchFile_ResponseTooLarge(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusOK)
+		// Write maxResponseBytes+1 bytes to exceed the cap.
+		chunk := make([]byte, 4096)
+		written := int64(0)
+		for written <= maxResponseBytes {
+			n, _ := w.Write(chunk)
+			written += int64(n)
+		}
+	}))
+	defer srv.Close()
+	cfg := GitLabConfig{BaseURL: srv.URL}
+	_, err := cfg.FetchFile("group/project", "/ci.yml", "main")
+	if err == nil {
+		t.Fatal("expected error for oversized response")
+	}
+	if !strings.Contains(err.Error(), "exceeds maximum size") {
+		t.Errorf("unexpected error: %v", err)
+	}
+}
+
+func TestFetchURL_ResponseTooLarge(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusOK)
+		chunk := make([]byte, 4096)
+		written := int64(0)
+		for written <= maxResponseBytes {
+			n, _ := w.Write(chunk)
+			written += int64(n)
+		}
+	}))
+	defer srv.Close()
+	cfg := GitLabConfig{}
+	_, err := cfg.FetchURL(srv.URL)
+	if err == nil {
+		t.Fatal("expected error for oversized response")
+	}
+	if !strings.Contains(err.Error(), "exceeds maximum size") {
+		t.Errorf("unexpected error: %v", err)
+	}
+}