fix: stop Reddit's block page reading as a signed-out session

Reddit answers a throttled client with a large HTML 403 interstitial. To
the comment client that was indistinguishable from a logged-out session:
the body would not parse, so no modhash was found, so it reported
"Reddit did not return a modhash for this session" and returned
session-invalid — which calls auth.invalidate() and so could disrupt
outreach and chat for an account whose session was perfectly healthy.

That matches what prod is doing. u/Saira_Makimad posted successfully 25
seconds after boot and every later attempt failed with that message,
which is the shape of Reddit starting to throttle rather than a session
going bad.

A response is now only treated as a verdict about the session when it is
actually JSON. Non-JSON, at any status, is Reddit refusing to serve us
and stays retryable. A genuine JSON 403, or JSON with no modhash, still
invalidates as before.

When Reddit does report a signed-out session, the log and the recorded
reason now name the cookies visible to the write origin — names and
domains only, never values. Cookies scoped to www.reddit.com rather than
.reddit.com would produce exactly this symptom, and this makes that
answerable from the logs instead of by guesswork.

Also clarify the allowance in the dashboard. It is derived from the trust
level rather than typed in, and it is a rolling 24-hour window, neither
of which the page said. A per-community cap above the account allowance
now says how much of it is actually reachable, because "1 of 10 today"
next to an account limit of 2 reads as far more headroom than exists.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/services/reddit-account-runtime-builder.ts

@@ -21,6 +21,7 @@ import {
 } from '../database/account-repositories.js';
 import { RedditApiClient, RedditRateLimitError, type RedditPost } from '../reddit/api.js';
 import {
+  REDDIT_WRITE_ORIGIN,
   RedditCommentClient,
   createAnonymousFetcher,
   createBrowserWriteTransport,
@@ -258,6 +259,13 @@ async function buildRuntime(
       {
         scheduler: redditRequestCoordinator,
         anonymousFetch: createAnonymousFetcher(accountConfig.reddit.userAgent),
+        // Names and domains only — never cookie values. This is the fastest way
+        // to see why Reddit stopped recognising a session on the write origin.
+        describeCookies: async () => {
+          const cookies = await browserClient.getContext()?.cookies(REDDIT_WRITE_ORIGIN) ?? [];
+          if (cookies.length === 0) return `none visible to ${REDDIT_WRITE_ORIGIN}`;
+          return cookies.map((cookie) => `${cookie.name}@${cookie.domain}`).join(', ');
+        },
       },
     );
     const growthService = new AccountGrowthService({