character create: editor URL 404s on non-English locales (default --locale en-US is not a valid Flow URL segment) #153

Summary

gflow character create fails on non-English Flow accounts because the character-editor URL is built with the raw BCP-47 --locale value (default en-US), but Flow's URL locale path segment is a short code (/fx/pt/..., /fx/en/...). The tool must be language-agnostic.

Repro

gflow character create --project <pid> --name X --face-prompt "..." on a pt-locale account (default --locale en-US).

Observed

• URL built: https://labs.google/fx/en-US/tools/flow/project/<pid>/character/<eid> (see routes.character_editor_url, api/routes.py).
• en-US is not a valid Flow locale segment → 404 → redirect to the account-locale 404 (https://labs.google/fx/pt/404).
• _enter_character_editor then fails: Character editor not ready: prompt textbox not visible within 20 s.

Confirmed cause

The recon spike scripts/dev/spike_char_editor_title.py defaults --locale pt and uses the same routes.character_editor_url() — it enters the editor fine. Production fails only because the default is the BCP-47 en-US.

Suggested fix (language-agnostic)

Normalize the locale to its primary subtag when building the editor URL, e.g. locale.split('-')[0].lower() → en-US→en, pt-BR→pt. Prefer deriving the segment from the account's actual Flow UI locale where available. Add a unit test pinning the URL form for en-US/pt-BR inputs.

Impact

Blocks character create on every non-en account using the default locale. Discovered while building the character promo (gflow-cli-remotion); worked around there by passing --locale pt, but the tool itself should not require it.