The OAuth callback at `/callback` previously fell back to
`window.opener.postMessage({ code, state, ... }, "*")` whenever the opener
was cross-origin. The fallback was intended to support remote-OmniRoute +
local-loopback callbacks (where opener and callback live on different
origins), but the same code path also delivers the OAuth code/state to any
hostile opener that pops the well-known callback URL — letting that
attacker complete the OAuth flow as the user.
Replace the wildcard fallback with iteration over a fixed allowlist:
`window.location.origin` (same-origin parent — the popup-mode dashboard)
plus Codex's fixed loopback helper (`http://localhost:1455` and the IPv4
literal `http://127.0.0.1:1455`). The browser drops `postMessage` to any
opener whose actual origin is not in `targetOrigin`, so the message reaches
only known parents and is silently dropped for any other. The same-origin
fallback path is unchanged — methods 2 (`BroadcastChannel`) and 3
(`localStorage` storage event) still cover same-origin openers that COOP
severed.
The `openerSameOrigin` probe stays in place to drive the auto-close vs
manual-copy UI decision (no behavior change for the success path).
Adds a regression test (`tests/unit/ui/oauth-callback-postmessage-scope.test.tsx`)
that mounts the page with a stubbed cross-origin opener and asserts no
`postMessage` call ever uses `"*"` and every call lands on an allowlisted
origin. The test failed against the pre-fix code (red), passes after the
fix (green) — TDD per CLAUDE.md hard rule #18.
Partial port of upstream decolua/9router#998: the upstream PR also
re-enabled TLS verification on a DNS-bypass fetch in `open-sse/utils/proxyFetch.js`;
that part is N/A here because OmniRoute's `proxyFetch.ts` never disabled
TLS verification (no `rejectUnauthorized: false` anywhere in the file).
Inspired-by: https://github.com/decolua/9router/pull/998
Co-authored-by: aeonframework <aeon@aeonframework.dev>
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