fix(#82): address Copilot review findings on firewall editor PR

- helpers.go: refresh sectionsJSON doc-comment — payload is embedded in a
  hidden <textarea>, not a <script type="application/json"> (the inline
  templ comment already noted this; the helper doc was stale).
- helpers.go: add shortSHA() — safe 12-char truncation that returns the
  original string when shorter than 12 chars, instead of panicking on a
  bounds-out-of-range slice.
- firewall_config.templ: use shortSHA(config.SHA256) for the header SHA
  display; document the non-nil `config` precondition in the templ
  doc-comment (the HTTP handler routes nil/error to
  FirewallConfigPageWithError, so the hidden input/textarea elements
  legitimately rely on it).
- editor.js: drop the unread `btn.dataset.line` assignment in
  makeNavButton — scrollToLine is invoked via the closure with
  section.start_line, so the dataset attribute was dead code.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: sarg3nt

gearbox/internal/framework/templates/pages/firewall_config.templ

@@ -8,6 +8,14 @@ import (
 )
 
 // FirewallConfigPage renders the firewall configuration editor page.
+//
+// Precondition: `config` must be non-nil. The HTTP handler routes the nil /
+// fetch-error case to FirewallConfigPageWithError, so by the time this
+// template is invoked the agent payload is known to exist. The hidden
+// input + textarea elements below dereference `config` unconditionally on
+// that basis; the optional `if config != nil` guard around the SHA /
+// timestamp header block is purely cosmetic (keeps the metadata strip
+// from rendering blanks if a future caller ever violates the contract).
 templ FirewallConfigPage(user *models.User, server *database.BoxDB, config *agent.FirewallConfigResponse, gitConfig *database.BoxGitConfig, changes []database.ConfigChange, canEdit bool) {
 	@layouts.Base("Firewall Configuration", user, "/config/firewall") {
 		<!-- Action toolbar hoisted to the global page header (right of the
@@ -19,7 +27,7 @@ templ FirewallConfigPage(user *models.User, server *database.BoxDB, config *agen
 				if config != nil {
 					<div class="hidden xl:flex items-center gap-3 text-xs text-gray-500 dark:text-gray-400 mr-2">
 						<span title="File last modified">{ config.LastModified.Format("2006-01-02 15:04:05") }</span>
-						<span class="font-mono">SHA { config.SHA256[:12] }</span>
+						<span class="font-mono">SHA { shortSHA(config.SHA256) }</span>
 					</div>
 				}
 				if canEdit {

gearbox/internal/framework/templates/pages/helpers.go

@@ -24,8 +24,10 @@ func canEditValue(canEdit bool) string {
 
 // sectionsJSON serializes the parsed nftables section list (tables + chains
 // with line numbers) so the editor JS can render the left-rail nav without
-// re-parsing the config client-side. Embedded into a `<script type="application/json">`
-// tag, so templ HTML-escapes it safely.
+// re-parsing the config client-side. Embedded into a hidden `<textarea>` (NOT
+// a `<script type="application/json">`) so templ HTML-escapes the body the
+// same way it does for any other interpolated text node — the JS reads
+// `.value` off the textarea and `JSON.parse`s it.
 func sectionsJSON(sections []agent.ConfigSection) string {
 	if len(sections) == 0 {
 		return "[]"
@@ -37,6 +39,17 @@ func sectionsJSON(sections []agent.ConfigSection) string {
 	return string(b)
 }
 
+// shortSHA truncates a hex digest to the first 12 characters for compact
+// display in the page header. Safe on short / empty input — returns the
+// original string unchanged if it's already shorter than the target.
+func shortSHA(s string) string {
+	const n = 12
+	if len(s) <= n {
+		return s
+	}
+	return s[:n]
+}
+
 // backendBelongsToFrontend checks if a backend is associated with a frontend via metadata.
 func backendBelongsToFrontend(backendName, frontendName string, metadata *models.Metadata) bool {
 	if metadata == nil {

gearbox/static/js/firewall_config/editor.js

@@ -265,7 +265,6 @@
 	function makeNavButton(section, kind) {
 		const btn = document.createElement('button');
 		btn.type = 'button';
-		btn.dataset.line = String(section.start_line || 1);
 		btn.className =
 			'w-full text-left px-2 py-1 rounded text-gray-300 hover:bg-gray-800 hover:text-white flex items-center gap-2';
 		const dot = document.createElement('span');