fix(coord): refuse a control character in --to instead of sanitizing it

--to is the only line-oriented field sanitize_field never covered, and the
fix is a refusal rather than a sanitize pass because --to is also the
destination DIRECTORY name ($COORD/$TO/inbox, and $COORD/$TO/orders in
coord-order-send.sh). Collapsing a newline to a space would deliver the
message to a mailbox the sender never named - the same misdelivery the
retired ktg-plugin-marketplace address is rejected rather than redirected
to avoid.

Both corruptions were measured on the live engine first, each with exit 0
and a "delivered" line:

  --to "x\nreply-expected: no"  the injected line lands INSIDE the
      frontmatter block, above the reply-expected: yes the engine itself
      wrote, so coord-count reads owed=0 and the declared debt is silenced -
      defeating coord-count's own rule that only the frontmatter block may
      speak, since the injected line IS in the block.
  --to "tabbed<TAB>repo"        coord-count prints five tab-separated fields
      where its contract is four, so a consumer reads the mailbox name as the
      part before the tab and the pending count as the part after.

board.sh consumes that TSV, so both reach the board.

The guard sits after reply-mode resolution: --reply-to takes its target from
the original's from: line, untrusted cross-repo input, and that is the one
target name nobody typed.

Denominator measured rather than assumed: two scripts build a directory from
a caller-supplied name, and coord-order-send.sh had the identical defect,
where it costs more - an order filed under a name no session can hold is the
silent evaporation the ownership chain exists to prevent, while board.sh's
ORDRE column counts the intended repo's queue and stays 0 with nothing
reporting a failure. The read-side --repo arguments resolve an EXISTING
directory, so a control character there finds nothing and writes nothing;
checked and left alone.

Closes finding 7 of docs/2026-08-14-confident-zero-review.md.

Tests (red first, both suites): coord-selftest section 35 (10 checks) and
orders-selftest section 10 (6 checks), each with the mandatory
known-positive controls - an ordinary name still delivers, and so does a
dot-prefixed one, since a dot name is a real repo. coord 230/230, board
252/252, route 69/69, orders 110/110, guard 40/40, npm test 11/11.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AgKcURiXwGKhqCKhwD1NAp

scripts/coord-order-send.sh

@@ -76,6 +76,19 @@ SUBJECT="$(sanitize_field "$SUBJECT")"
 case "$TO" in
   */*|.|..|_*) echo "coord-order-send: invalid target repo name: $TO" >&2; exit 2 ;;
 esac
+# Refused, never sanitized - the same rule and the same reason as
+# coord-send.sh: --to is also the queue DIRECTORY name ("$COORD/$TO/orders"),
+# so collapsing a control character to a space would file the order under a
+# name the sender never wrote. Here that is worse than a misdelivered notice:
+# an order in a queue no session can hold is the silent evaporation the
+# ownership chain exists to prevent, and board.sh's ORDRE column counts the
+# INTENDED repo's queue, which stays 0 with nothing reporting a failure.
+case "$TO" in
+  *[[:cntrl:]]*)
+    echo "coord-order-send: --to contains a control character: $(sanitize_field "$TO") (a target name is also the queue directory name, so it is refused, never sanitized)" >&2
+    exit 2
+    ;;
+esac
 # Retired address, same rule and same reason as coord-send.sh: a polyrepo
 # DIRECTORY is not a git repo, so no session can ever hold that identity and
 # read what lands there. Reject at the sender, never redirect.