Fix the shared Claude auth flow: whole sign-in URL, recoverable rejected code

Two compounding bugs made `claude setup-token` unusable, both measured against
2.1.226 under a pty rather than reasoned about.

**The sign-in URL was truncated.** The CLI emits it as an OSC 8 hyperlink and
slices the *visible* text of that hyperlink to the terminal width: a 346
character URL arrives at 80 columns as five separate hyperlink emissions, each
carrying the whole URL in its parameter and 80 characters of it on screen. The
transcript scraper picked up the first slice — a URL that parses, points at
claude.com, and cannot authorise anything. The ANSI stripper now surfaces the
OSC 8 target and `claude-token-link` carries it to the UI, which prefers it over
the scraped text. It still goes through `sanitizeRelayUrl` with the
ANTHROPIC_SIGN_IN_HOSTS allowlist before display and again before `openUrl` — an
OSC 8 parameter is never rendered, which makes it the easier place to hide a
hostile host, not a trusted one. The wrapped-display fallback is kept for CLI
versions that print a bare URL.

**A rejected code hung the flow.** On a bad paste the CLI prints `OAuth error:
Invalid code…` / `Press Enter to retry.` and blocks on stdin instead of exiting;
nothing recognised that, so the exec sat until the 15-minute timeout with the UI
still saying "Finishing sign-in". Given the first bug handed the user a truncated
URL, an invalid code was the likely first outcome. The streamed output is now
scanned for that message, `claude-token-code-rejected` reopens the input with an
explanation, and the Enter is sent so the next code has a prompt to land in —
bounded by MAX_CODE_ATTEMPTS, after which the flow reports a failure. An
undeterminable exec exit status is logged rather than silently read as success.

**A wrapped token was rejected *and* leaked.** `stty cols` fails silently, and an
80-column fallback splits the ~103 character token across two lines: the parser
saw a too-short fragment and failed, while the redactor masked the first line —
which carries the `sk-ant-` marker — and printed the second, the tail of a live
credential, to the UI in clear. `scan_credential_body` now reassembles a run
across hard wraps and both the parser and the redactor use it, so they cannot
disagree about where a credential ends. A join only happens across a break at a
plausible terminal margin (>= 40 columns) and only for a run not already long
enough to be a whole credential — without that second guard a repainting TUI
welds one frame's token onto the next frame's first word. The length floor is
applied to the reassembled body, so a fragment is still never accepted.

Also: `stty cols` raised 200 -> 400 (the URL alone needs ~350), and `ESC ( B` is
handled as the three-byte charset designation it is — it prefixes every repaint
frame, and treating it as two bytes emitted a stray `B` that could glue itself
onto a token and make the parser refuse it.

`submit_claude_token_code`'s single-write behaviour is unchanged.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01KSP2KNPhuWKQ4DL5TZEn3k

TECHNICAL.md

@@ -245,9 +245,31 @@ minutes.
 
 - **Storage** — the OS keychain, under a dedicated service name; the token is never returned to the
   frontend, never written to a log, and no command accepts or returns it.
+- **The sign-in URL comes from the OSC 8 parameter, not the screen.** The CLI emits the URL as a
+  hyperlink and slices the *visible* text of it to the terminal width — measured against 2.1.226, a
+  346-character URL arrives at 80 columns as five separate hyperlink emissions, each carrying the
+  whole URL in its parameter and 80 characters of it on screen. Scraping the visible text yields a
+  URL that parses, points at `claude.com`, and cannot authorise anything, so the ANSI stripper
+  surfaces the hyperlink target and `claude-token-link` carries it to the UI. The frontend applies
+  the `ANTHROPIC_SIGN_IN_HOSTS` allowlist to it before display and again before `openUrl` — an OSC 8
+  parameter is container output that is never rendered, which makes it the *easier* place to hide a
+  hostile host, not a trusted one. `stty cols 400` (up from 200, which the URL still overflowed)
+  removes wrapping as a variable elsewhere, but it is not the fix: that line fails silently.
+- **A rejected code is recoverable, not a hang.** On a bad paste the CLI prints
+  `OAuth error: Invalid code…` / `Press Enter to retry.` and blocks on stdin rather than exiting.
+  The streamed output is scanned for that, `claude-token-code-rejected` reopens the input with an
+  explanation, and the Enter is sent so the next code has a prompt to land in — bounded by
+  `MAX_CODE_ATTEMPTS`, after which the flow reports a failure. Without this the exec sat until the
+  15-minute timeout with the UI still saying "Finishing sign-in".
 - **Redaction** — streamed output is stripped of ANSI sequences and passed through a stateful
   redactor that masks anything matching `sk-ant-` with a plausible body, withholding any tail that
-  could still grow into a secret across a chunk boundary.
+  could still grow into a secret across a chunk boundary. A credential split across a hard line
+  wrap is reassembled by both the parser and the redactor from the same `scan_credential_body`, so
+  the two cannot disagree about where a credential ends — previously a wrapped token was rejected
+  as too short *and* its second line, which carries no `sk-ant-` marker, was printed to the UI in
+  clear. A run is only joined across a break that sits at a plausible terminal margin and is not
+  already long enough to be a whole credential; otherwise a repainting TUI would weld one frame's
+  token onto the next frame's first word.
 - **Injection** — `CLAUDE_CODE_OAUTH_TOKEN` is set only when the backend is Anthropic, the project
   has not opted out (`use_shared_auth_token`, default `true`), and a non-blank token is stored. When
   those conditions do not hold, the variable is explicitly set to empty rather than omitted, so a