Salvages the two still-valid hardenings from #5381 onto the relocated
plugin adapters (the discord/feishu/whatsapp adapters moved to
plugins/platforms/ since the PR was opened, and 4 of its 6 hunks are
already on main or superseded).
- feishu: rate limiter now denies untracked keys when the tracking table
is at capacity after pruning stale entries (was: allow through without
tracking). At-capacity-with-all-fresh-entries only happens under abuse,
so allowing untracked requests let an attacker who flooded the table
bypass the limiter entirely. Already-tracked keys and post-prune room
are unaffected.
- whatsapp: absolute file paths handed back by the Baileys bridge are now
validated to resolve inside a known media cache dir before being
attached. A compromised/buggy bridge could otherwise return an
arbitrary path (e.g. /etc/passwd) that would be sent verbatim to the
model. Guard resolves symlinks and accepts both the canonical
cache/<kind> and legacy <kind>_cache layouts.
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