diff --git a/AGENTS.md b/AGENTS.md
index 38ca2ae..5cd9fae 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -50,10 +50,21 @@ After `npm test`, use `npm run dev` and confirm:
   in both light and dark themes and at a narrow window width, and values
   persist across a restart.
 - The right-click **Ask ChatGPT** item appears only when text is selected.
-- `Alt+Shift+G` acts on the selection, including a selection inside an iframe,
-  and opens a blank chat when nothing is selected or on a restricted page such
-  as `about:config`. Press the key to test this — `commands.getAll()` reports a
-  shortcut as registered even when Firefox has silently overridden it.
+- `Alt+Shift+G` acts on the selection and opens a blank chat when nothing is
+  selected or on a restricted page such as `about:config`. Press the key to test
+  this — `commands.getAll()` reports a shortcut as registered even when Firefox
+  has silently overridden it. The injected snippet is gated on
+  `document.hasFocus()`, so cover all four frame cases:
+  - Select in the top frame → the top-frame text arrives.
+  - Select inside an iframe → the iframe text arrives.
+  - Select in the top frame, *then* select inside an iframe → the iframe text
+    arrives. `hasFocus()` is true for a focused frame and all its ancestors, so
+    if the stale top-frame text arrives instead, exclude ancestors by also
+    checking that `document.activeElement` is not the frame element.
+  - Press `Ctrl+F`, find a term, then press the shortcut without clicking back
+    into the page → a blank chat is expected. Firefox leaves focus in the
+    findbar, so no content frame reports focus. This is a deliberate trade: a
+    stale cross-origin frame silently seeding the prompt was the worse failure.
 
 Inspect ZIP contents whenever packaging rules or assets change; `test/` and
 `docs/` must never appear, not even as empty directory entries.
diff --git a/lib/build-url.js b/lib/build-url.js
index 10e3e08..398828b 100644
--- a/lib/build-url.js
+++ b/lib/build-url.js
@@ -56,6 +56,9 @@ function lastWhitespaceIndex(text) {
 }
 
 // Returns the longest prefix of `prompt` whose finished URL fits the budget.
+// The guarantee assumes `settings` came through mergeSettings(): only `q` is
+// ever trimmed, so a model longer than MAX_MODEL_CHARS could blow the budget on
+// its own and leave no room for `q` at all. Every real caller goes via load().
 // Slicing happens by CODE POINT on the decoded string, so a surrogate pair can
 // never be split and a percent-escape can never be severed (encoding happens
 // afterwards, via URLSearchParams).
diff --git a/options/options.html b/options/options.html
index 8920222..2ebd7cd 100644
--- a/options/options.html
+++ b/options/options.html
@@ -9,7 +9,9 @@
 <form id="settings" autocomplete="off">
   <div class="field">
     <label for="model">Model <span class="tag">experimental</span></label>
-    <input type="text" id="model" placeholder="auto" spellcheck="false" maxlength="200" />
+    <!-- maxlength is set from MAX_MODEL_CHARS in options.js, so the input and
+         mergeSettings() can never disagree about the bound. -->
+    <input type="text" id="model" placeholder="auto" spellcheck="false" />
     <p class="hint">
       ChatGPT may ignore this and use your account default. Leave blank to
       always use your account default.
diff --git a/options/options.js b/options/options.js
index cc1ef03..371a192 100644
--- a/options/options.js
+++ b/options/options.js
@@ -1,4 +1,4 @@
-import { DEFAULT_SETTINGS } from "../lib/defaults.js";
+import { DEFAULT_SETTINGS, MAX_MODEL_CHARS } from "../lib/defaults.js";
 import { load, save } from "../lib/settings.js";
 
 const SAVE_DEBOUNCE_MS = 400;
@@ -59,6 +59,11 @@ function scheduleSave() {
   saveTimer = setTimeout(() => persist(collect()), SAVE_DEBOUNCE_MS);
 }
 
+// Derived rather than hard-coded in the markup: if the two ever disagreed, the
+// input would accept a model that mergeSettings() then silently discards,
+// blanking the setting with no explanation.
+field("model").maxLength = MAX_MODEL_CHARS;
+
 // Module scripts are deferred, so the DOM is already parsed here.
 render(await load());