fix(mobile): links open in a new tab from a tap, in the terminal and the chat

On a phone no link was openable, on either surface, for two unrelated reasons.

**Terminal.** xterm resolves the link under the pointer on `mousemove` and
activates it on `mouseup` over its SCREEN element. A touch tap delivers neither:
`touch-action: none` on the terminal subtree plus touchstart's preventDefault for
a 'content' tap suppress the browser's compatibility mouse events,
`_installMobileTapMouseGuard` drops the trusted ones that still arrive inside the
450ms tap window, and the synthetic mousedown/mouseup pair dispatched for mouse
REPORTING goes to the `.xterm` root — an ancestor of the node the linkifier
listens on, so it cannot reach it — and carries no mousemove either way. Every
URL and file path in the terminal was therefore inert on phones and tablets,
Claude Code's own `/login` URL included.

The tap path now activates the link itself, through the SAME provider that feeds
the hover linkifier (`_terminalLinkAtPoint`), so a tap and a desktop click can
never disagree about what is a link or where it ends — containment mirrors
xterm's own `_linkAtPosition`. It runs synchronously inside the touchend handler,
which is what keeps the user gesture that lets `window.open` past the popup
blocker, and before any mouse report, exactly as `_handleDesktopTerminalClick`
already skips the SGR tap for a hovered link.

Two kinds of row keep their existing meaning: the caret's logical line, where a
tap places the cursor and a URL the user typed must stay editable, and TUI-owned
rows, where a numbered choice or an expandable readback is answering a dialog and
routinely carries the very path the tap would otherwise open. The caret line is
the boundary rather than the tap intent, because a plain shell classifies EVERY
tap as 'input' and gating on that would leave every URL in shell output inert.

**Chat.** `marked` emits a bare `<a href>` and the markdown sanitizer's allowlist
carries no `target`, so a tap in the response viewer navigated the current tab
away: on a phone that unloads the whole dashboard — SSE, terminal buffers, unsent
composer text — and there is no middle-click or open-in-new-tab affordance to
work around it. `_renderMarkdown` now decorates anchors in the template pass it
already makes for code blocks. That pass runs AFTER sanitizing, so it is the only
source of both attributes: an agent-authored `target`/`rel` is already stripped,
and `rel="noopener noreferrer"` is set on the same element in the same breath, so
no page Codeman opens gets a `window.opener` handle back. Fragment links stay
in-page; mailto:/tel: are left to the OS rather than stranding an empty tab.

Tests: 10 cases in `terminal-touch-tap.test.ts` (URL, file path, log path,
scrollback, no-double-report, composer, shell mode, dialog row, no provider) and
a new `response-viewer-external-links.test.ts` driving the shipped marked +
DOMPurify + app.js. 7 of them fail without the fix.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/web/public/app.js

@@ -2053,6 +2053,28 @@ class CodemanApp {
           wrap.appendChild(actions);
           wrap.appendChild(pre);
         });
+        // Links open in a NEW tab.
+        //
+        // marked emits a bare `<a href>` and the sanitizer's allowlist has no
+        // `target`, so a tap in the chat NAVIGATED THE APP AWAY: on a phone that
+        // unloads the whole dashboard — SSE, terminal buffers, unsent composer
+        // text — and the OS back gesture reloads it from scratch, which is what
+        // "links don't open" reads as on mobile, with no middle-click or
+        // open-in-new-tab affordance to work around it.
+        //
+        // This pass runs AFTER sanitizing, so it is the only source of these two
+        // attributes: whatever an agent wrote is already gone, and `rel` is set on
+        // the same element in the same breath, so no page Codeman opens ever gets
+        // a `window.opener` handle back (reverse tabnabbing).
+        //
+        // A fragment link stays in-page, and mailto:/tel: are handed to the OS —
+        // giving those a target just strands an empty tab.
+        tmpl.content.querySelectorAll('a[href]').forEach((a) => {
+          const href = a.getAttribute('href') || '';
+          if (!href || href.startsWith('#') || /^(?:mailto|tel):/i.test(href)) return;
+          a.setAttribute('target', '_blank');
+          a.setAttribute('rel', 'noopener noreferrer');
+        });
         return tmpl.innerHTML;
       } catch { /* fall through */ }
     }