fix(file-preview): let rendered Markdown fill the resized window

.changeset/file-preview-md-width.md

@@ -0,0 +1,5 @@
+---
+'aicodeman': patch
+---
+
+The rendered markdown in the File Viewer now fills the window as the window grows. The rule carried a fixed 960px reading column that shipped before the window could be resized, so text stopped reflowing once the window was dragged or expanded past it, while the plain-text view already filled it. A narrow window is unchanged, because a cap only binds when content is wider than it. Pinned by test/file-preview-window.test.ts.

src/web/public/styles.css

@@ -12544,13 +12544,17 @@ html:is([data-skin="paper-gray"], [data-skin="solarized-light"], [data-skin="cat
 
 /* ---- File Viewer rendered markdown ----
    Styling comes from the Response Viewer's .rv-text rules; .rv-text itself
-   carries no padding or base font (the chat card supplies those). */
+   carries no padding or base font (the chat card supplies those).
+
+   No width cap. The window is whatever the user drags or expands it to, so the
+   document must reflow to fill it; the fixed 960px reading column this rule
+   shipped before the resize grip existed stops reflow once the window is wider
+   than the cap. Pinned by test/file-preview-window.test.ts. */
 
 .file-preview-body > .file-preview-md {
   padding: 1rem 1.25rem 2rem;
   font-size: 15px;
   line-height: 1.55;
-  max-width: 960px;
 }
 
 /* Relative links in the document are rebased onto a.rv-path so the Response

test/file-preview-window.test.ts

@@ -14,7 +14,9 @@
  *   9. stepping onto a folder-grid page moves the grid's own index with it,
  *  10. Alt+←/→ steps, ignores other chords and text fields, and is swallowed at the ends,
  *  11. the corner grip doubles the pointer delta and clamps the size,
- *  12. phones ignore Expand and the grip (mobile.css).
+ *  12. phones ignore Expand and the grip (mobile.css),
+ *  13. the rendered document carries no width cap, so it fills the window the
+ *      grip and Expand give it (styles.css).
  *
  * Loaded via `vm` against a stub app, same harness style as file-preview-detach.test.ts.
  */
@@ -27,6 +29,7 @@ import { describe, expect, it, vi } from 'vitest';
 const PUBLIC = resolve(import.meta.dirname, '../src/web/public');
 const panelsJs = readFileSync(resolve(PUBLIC, 'panels-ui.js'), 'utf8');
 const indexHtml = readFileSync(resolve(PUBLIC, 'index.html'), 'utf8');
+const stylesCss = readFileSync(resolve(PUBLIC, 'styles.css'), 'utf8');
 
 function btn() {
   const attrs: Record<string, string> = {};
@@ -376,6 +379,21 @@ describe('file viewer resize grip', () => {
   });
 });
 
+describe('file viewer rendered markdown width', () => {
+  it('carries no fixed reading column, so the document fills the window the grip and Expand give it', () => {
+    const mdRule = stylesCss.match(/\.file-preview-body > \.file-preview-md \{[^}]*\}/);
+    expect(mdRule, 'the rule the rendered document lives in').not.toBeNull();
+    // Any cap here reflows nothing once the window is wider than it, which is
+    // what the shipped 960px column did. The window width is the user's choice,
+    // so nothing in this rule may cap it.
+    expect(mdRule![0], 'no width cap on the document').not.toMatch(/max-width/);
+    // The shared .rv-text prose rule must not reintroduce one either.
+    const rvBase = stylesCss.match(/\.rv-text,\s*\.response-viewer-body > :not\(\.rv-message\) \{[^}]*\}/);
+    expect(rvBase, 'the shared prose rule').not.toBeNull();
+    expect(rvBase![0], 'no width cap on the shared prose rule').not.toMatch(/max-width/);
+  });
+});
+
 describe('file viewer on phones', () => {
   it('overrides Expand and any dragged size, and hides both controls, under 600px', () => {
     const css = readFileSync(resolve(PUBLIC, 'mobile.css'), 'utf8');