Shift+Enter newline, OAuth URL truncation, and the auth bridge toggle

Three fixes that all land on the same journey: sign in, paste a prompt,
and have the terminal behave the way every other Claude Code host does.

Shift+Enter inserts a newline
-----------------------------
xterm.js does not consult `shiftKey` for Enter (`Keyboard.ts`, case 13),
so Shift+Enter was byte-identical to Enter and submitted the prompt.
Both terminals now send `\x1b\r` (ESC+CR) instead, which Claude Code
parses as return+meta — the same bytes its own `/terminal-setup` writes
into the VS Code, Cursor, Alacritty and Zed keymaps, so this is in-band
rather than a guess. Not `\n`: Claude Code accepts it, but a shell would
run the line, so the two session types would diverge. Bound in Claude
sessions only for that reason.

`entrypoint.sh` sets `shiftEnterKeyBindingInstalled` in `~/.claude.json`
so the CLI stops printing its "run /terminal-setup" tip. Purely
cosmetic — the decoding is unconditional either way.

Alt+Enter has always done the same thing (xterm ESC-prefixes on altKey)
and was simply never documented. It is now, along with the rest.

OAuth login URL truncation
--------------------------
Two producers wrote one toast slot, last-writer-wins. The OSC 7777 relay
delivers the URL base64-encoded and therefore exact; ~300 ms later the
screen-scraper's debounce fired and overwrote it with a truncated guess
at the same link — a URL that parses, points at the right host, and
authorises nothing. The user is the one who has to notice.

Why the scraper truncated: `ANSI_RE` strips OSC sequences wholesale,
including the OSC 8 hyperlink whose parameter carries the complete URL.
Claude Code slices the *visible* text of that hyperlink to the terminal
width while every emission carries the whole URL in its parameter. The
backend already knew this (`commands/auth_token_commands.rs`); the
frontend did not.

- `urlDetector` now reads OSC 8 targets out of the raw buffer before
  stripping, filtered by a port of `usable_sign_in_link`, and tags every
  candidate with its provenance.
- The prompt slot gained `supersedes`: better provenance always wins,
  worse never does, and between equals only a candidate that *extends*
  what is showing may replace it. That last rule is `extendsUrl`,
  factored out of `pickSignInUrl` rather than copied — same rule, same
  reason, one implementation.
- `flatten` splits on a bare `\r` as well as on `\r?\n`, so a
  `\r`-repainted TUI frame no longer inflates a line past the width and
  suppresses a join that should have happened; and the width is now
  sampled at `feed()` rather than read at `scan()`, so a resize inside
  the 300 ms debounce cannot reassemble 80-column text against a
  120-column rule.

Also corrects the comment claiming `acquire_claude_token` enables the
auth bridge. It deliberately does not, and the module comment in
`auth_token_commands.rs` explains at length why not.

The auth bridge toggle
----------------------
`setAuthBridgeEnabled` and `getAuthBridgeStatus` had zero call sites:
the Rust was complete, the IPC wrapper shipped, and there was nowhere to
click — so the docs told users to "enable the Auth Bridge" for a switch
that did not exist. `AuthBridgeRow` is that switch, in Config → Runtime.
It deliberately does not go through the tab's stopped-only save: the
dedicated command exists so the bridge can be flipped while a login is
hanging in a running container, which is the only moment anyone reaches
for it.

It also subscribes to `auth-bridge-changed`, which the poller has been
emitting to nobody — so a host port the bridge could not take was a
completely silent failure, indistinguishable from a login that hung.

`tunnel.rs` promotes the best-effort `::1` bind failure from debug to a
warning recorded on the port. Half-bound is the failure mode that looks
like success: the status says bridged, and a client that resolves
`localhost` to `::1` without falling back is still refused.

Finally, for a recognised Anthropic sign-in URL the toast now leads with
"In container" and demotes the host "Open". The callback listener is
inside the container, so the container-side browser closes the loop with
no host round trip and no auth bridge; the host button stays as the
fallback. Ordinary URLs are unchanged.

Tests: 402 frontend (was 359), 285 Rust (unchanged).

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GBq2rGum6GX7xXgsas1fDc

app/src/lib/urlRelay.ts

@@ -158,6 +158,42 @@ export function sanitizeRelayUrl(
   return normalized;
 }
 
+/**
+ * Whether `next` is the same link as `current`, only longer.
+ *
+ * The single rule that lets a later candidate displace an earlier one when both
+ * were scraped from the same untrusted stream. A repainting TUI lands a
+ * truncated copy of a link in the transcript before the complete one, and this
+ * is what joins them back up — safely, because a longer string sharing a prefix
+ * with the current pick necessarily has the same scheme, host and port, so an
+ * attacker cannot use it to move the origin.
+ *
+ * Longest-wins without the prefix test is what this replaced, and it handed the
+ * choice to the attacker: pad a hostile URL and it displaces the real one.
+ *
+ * Used by `pickSignInUrl` (`hooks/useClaudeAuth.ts`) and by the terminal's URL
+ * prompt slot (`components/terminal/TerminalView.tsx`). One implementation, on
+ * purpose.
+ */
+export function extendsUrl(next: string, current: string): boolean {
+  return next.length > current.length && next.startsWith(current);
+}
+
+/**
+ * Whether this is a URL that signs the user in to Anthropic.
+ *
+ * Used to decide *presentation*, not permission — the toast makes the
+ * container-side browser the default action for these, because the OAuth
+ * callback listener is inside the container and the host has nothing to catch
+ * it with. It is deliberately the same host allowlist the sign-in flow itself
+ * uses, so the two cannot disagree about what a sign-in link is.
+ */
+export function isAnthropicSignInUrl(url: string): boolean {
+  const safe = sanitizeRelayUrl(url, { allowHosts: ANTHROPIC_SIGN_IN_HOSTS });
+  if (!safe) return false;
+  return /oauth|authorize|login|sign-?in/i.test(safe);
+}
+
 /**
  * The origin of an already-sanitized URL, for display.
  *