ask-forum: harden per high-effort review + document capability limits

Fixes from the code-review workflow (7 findings): page the poll cursor past the
100-msg window (no false timeout behind bot/overflow messages); honor 429
retry_after and bail fast on permanent Discord errors (10003/50001/...) instead
of burning the timeout; status-check overflow follow-up chunks (warn, don't
silently truncate); clamp --read limit safely (guard >64-bit overflow); add
--wait --after for precise resumption; DRY the newline-trim; set LC_ALL=C.UTF-8
for codepoint-safe slicing. SKILL.md gains the tested bot capability/limit map
(can: post/read/edit-own/react; cannot without a grant: delete/archive/unlock/pin)
and a robustness section.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.claude/skills/ask-forum/SKILL.md

@@ -36,8 +36,27 @@ bash .claude/scripts/ask-forum.sh --read <thread_id>
 
 # Resume blocking on an already-posted thread (e.g. after a timeout):
 bash .claude/scripts/ask-forum.sh --wait <thread_id> --timeout 1800 --poll 10
+#   add --after <msg_id> to wait for replies STRICTLY AFTER a message you already
+#   consumed (default baseline catches any reply since the thread's starter).
 ```
 
+## Robustness (hardened after the 2026-07-08 review)
+- **Pages past the 100-message window:** the poll advances its `after` cursor each
+  cycle, so a reply is found even behind many bot/overflow messages (no false timeout).
+- **Rate-limit aware:** a `429` is honored (sleeps `retry_after`); a permanent Discord
+  error (Unknown Channel 10003, Missing Access 50001, etc.) **bails immediately** instead
+  of burning the full timeout; only genuine transients keep polling.
+- **Long questions** (>1900 chars) chunk into the starter + follow-up messages, and each
+  overflow POST is status-checked (warns if one drops, so the question isn't silently
+  truncated).
+- **`--wait` baseline** is the thread's starter id (starter id == thread id for a forum
+  post), so a reply that arrived *before* the wait started is caught, not missed. Because
+  of this, `--wait` on a thread that already holds a consumed answer re-returns it — pass
+  `--after <msg_id>` when you only want the NEXT reply.
+- Residual caveat: content slicing assumes a UTF-8 locale (the script sets
+  `LC_ALL=C.UTF-8`); a forced byte-counting `LC_ALL=C` could split a multibyte char at the
+  1900-char cut. Not an issue under the fleet default locale.
+
 Flags: `--title "short title"` (forum post name; defaults to first 60 chars of the
 question) · `--timeout SEC` (default 600) · `--poll SEC` (default 8) · `--tag @<id>`
 (repeatable — pings that person). Discord IDs: mike `264814939619721216`,