fix(workspace-server): strip JSON5 // comments from manifest.json before parsing

The Integration Tester appends "// Triggered by ..." to manifest.json after cloning.
Go's json.Unmarshal rejects it with "invalid character '/' after top-level value",
which causes E2E Chat to deterministically fail in CI (the E2E Chat stage uses
a dev-mode runtime-registry that reads from the cloned manifest).

Fix: strip trailing // comments from manifest.json before passing to json.Unmarshal.
This mirrors the approach already used in clone-manifest.sh for the same problem.

Fixes internal#1480.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

workspace-server/internal/handlers/runtime_registry.go

@@ -96,13 +96,70 @@ var fallbackRuntimes = map[string]struct{}{
 // Caller logs + falls back to fallbackRuntimes on any error. Not
 // returning the fallback here ourselves so the caller can decide
 // how loud to be about the miss (prod = WARN, tests = silent).
+// stripJSON5Comments removes a JSON5-style // trailing comment from manifest.json.
+// The Integration Tester appends "// Triggered by ..." at the very end of the file.
+// This comment is always after the final closing brace, so we scan only that
+// suffix rather than trying to track string-context across the whole file.
+// This avoids false-positives on legitimate // in URL values (e.g. http://foo.com/bar).
+func stripJSON5Comments(data []byte) []byte {
+	// Find the last '}' — everything before it is guaranteed standard JSON.
+	lastBrace := -1
+	for i := len(data) - 1; i >= 0; i-- {
+		if data[i] == '}' {
+			lastBrace = i
+			break
+		}
+	}
+	if lastBrace == -1 {
+		return data // no JSON structure found — return as-is, json.Unmarshal will error
+	}
+	// Everything after lastBrace is the trailing suffix to clean.
+	suffixStart := lastBrace + 1
+	if suffixStart >= len(data) {
+		return data // no suffix
+	}
+	suffix := data[suffixStart:]
+	// Strip leading whitespace at the start of the suffix.
+	cleanSuffix := trimLeadingWhitespace(suffix)
+	if len(cleanSuffix) == 0 || cleanSuffix[0] != '/' {
+		return data // suffix is empty or starts with non-comment — nothing to strip
+	}
+	// Remove the trailing comment (everything from the first // to end of file).
+	// Rebuild: prefix + suffix with comment stripped.
+	before := data[:suffixStart]
+	// Trim trailing whitespace from before so we don't leave a dangling newline.
+	trimmedBefore := trimTrailingWhitespace(before)
+	// Append a single newline so the JSON file ends cleanly.
+	result := append(trimmedBefore, '\n')
+	return result
+}
+
+func trimLeadingWhitespace(b []byte) []byte {
+	i := 0
+	for i < len(b) && (b[i] == ' ' || b[i] == '\t' || b[i] == '\n' || b[i] == '\r') {
+		i++
+	}
+	return b[i:]
+}
+
+func trimTrailingWhitespace(b []byte) []byte {
+	i := len(b)
+	for i > 0 && (b[i-1] == ' ' || b[i-1] == '\t' || b[i-1] == '\n' || b[i-1] == '\r') {
+		i--
+	}
+	return b[:i]
+}
+
 func loadRuntimesFromManifest(path string) (map[string]struct{}, error) {
 	data, err := os.ReadFile(path)
 	if err != nil {
 		return nil, err
 	}
+	// The Integration Tester appends "// Triggered by ..." to manifest.json.
+	// json.Unmarshal rejects it; strip // comments first (same as clone-manifest.sh).
+	clean := stripJSON5Comments(data)
 	var m manifestFile
-	if err := json.Unmarshal(data, &m); err != nil {
+	if err := json.Unmarshal(clean, &m); err != nil {
 		return nil, err
 	}
 	out := map[string]struct{}{

workspace-server/internal/handlers/runtime_registry_test.go

@@ -83,6 +83,70 @@ func TestLoadRuntimesFromManifest_MalformedJSON(t *testing.T) {
 	}
 }
 
+func TestLoadRuntimesFromManifest_TrailingJSON5Comment(t *testing.T) {
+	// The Integration Tester appends "// Triggered by Integration Tester at ..."
+	// to manifest.json after cloning. json.Unmarshal rejects it; stripJSON5Comments
+	// must remove the trailing comment so load succeeds.
+	dir := t.TempDir()
+	path := filepath.Join(dir, "manifest.json")
+	_ = os.WriteFile(path, []byte(`{
+		"workspace_templates": [
+			{"name": "langgraph", "repo": "org/t"}
+		]
+	}
+	// Triggered by Integration Tester at 2026-05-10T08:52Z`), 0600)
+
+	got, err := loadRuntimesFromManifest(path)
+	if err != nil {
+		t.Fatalf("load failed despite trailing comment: %v", err)
+	}
+	if _, ok := got["langgraph"]; !ok {
+		t.Errorf("langgraph missing from result: %v", keys(got))
+	}
+}
+
+func TestStripJSON5Comments(t *testing.T) {
+	cases := []struct {
+		name string
+		in   string
+		want string
+	}{
+		{
+			name: "trailing comment after closing brace removed",
+			in:   "{}\n// Triggered by Integration Tester\n",
+			want: "{}\n",
+		},
+		{
+			name: "embedded_in_url_preserved",
+			in:   `{"url":"http://foo.com/bar"}`,
+			want: `{"url":"http://foo.com/bar"}`,
+		},
+		{
+			name: "no_closing_brace_returns_input_unchanged",
+			in:   "no json here // comment",
+			want: "no json here // comment",
+		},
+		{
+			name: "comment_only_after_closing_brace_stripped",
+			in:   `{"a":1}` + "\n// Triggered by Integration Tester at 2026-05-10T08:52Z",
+			want: `{"a":1}` + "\n",
+		},
+		{
+			name: "clean_json_unchanged",
+			in:   `{"workspace_templates":[]}` + "\n",
+			want: `{"workspace_templates":[]}` + "\n",
+		},
+	}
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			got := string(stripJSON5Comments([]byte(tc.in)))
+			if got != tc.want {
+				t.Errorf("stripJSON5Comments(%q): got %q, want %q", tc.in, got, tc.want)
+			}
+		})
+	}
+}
+
 // TestRealManifestParses — sanity check against the actual
 // monorepo manifest.json so a future schema change to that file
 // (e.g. workspace_templates → workspace_runtime_templates) surfaces