Consolidated defensive layer for the invalid_blocks / msg_too_long bug
class (#56615, #62054, #53693): one malformed or oversized block fails
the ENTIRE chat.postMessage / chat.update call, so approval cards never
update and messages silently drop.
New block_kit.sanitize_blocks() is applied at every call site that
attaches blocks (send/edit via _maybe_blocks, send_exec_approval,
send_slash_confirm, and the approval/slash-confirm chat.update button
handlers). It:
- truncates section/context text to the 3000-char cap with an ellipsis
(covers interaction payloads where Slack's HTML-escaping of < > &
inflates text past the limit budgeted at send time)
- truncates header text to its 150-char cap
- drops empty blocks (no text / elements / rows)
- replaces null table column_settings entries with {} and trims
default trailing entries (Slack requires every entry be an object)
- caps the payload at Slack's 50-block maximum
- returns None when nothing valid remains so callers fall back to the
plain-text payload; never raises
Also registers contributor mappings for the salvaged PRs in this
cluster (tw0316, kamonspecial, sowork-skills).
