feat(engine): let a message say it needs no answer, and count debt without losing sight of the rest

Rule 7 (0.5.0) shipped an obligation on a format with four fields, none of
which could tell a question from a notice. Two consequences fell out of that
gap: the injection had to name both terminal states and prefer neither, and
coord-count.sh had to treat every unarchived file as a reply owed. The fifth
field closes both.

coord-send.sh --fyi writes reply-expected: no; omitting it writes yes. Absent
means expected, because every message already on disk lacks the field - so a
forgotten flag over-counts debt, which is visible, rather than creating debt
nobody sees. A reply is not a special case. A broadcast is always no: --reply-to
resolves inside the recipient's own mailbox and a broadcast never lands there,
so there is no reply path to promise.

coord-count.sh now prints TWO integers per mailbox, not one. Replacing pending
with debt was the obvious reading of "count debt rather than unarchived
messages" and it is wrong here: board.sh counts the same inbox files itself, so
a debt-only count would put two different numbers under one name with nothing to
reconcile them, and a mailbox holding only notices would read as empty while its
messages keep being re-injected.

The field is frontmatter and only frontmatter - a body line claiming
"reply-expected: no" at column 0 cannot silence a real debt, and a file without
valid frontmatter counts as owing a reply.

Section 20's wording changed because its stated reason expired, but its second
half matters more now, not less: the marking is a DECLARATION, not an
instruction. Without that clause one word in an untrusted message becomes a
lever that mints obligations in another repo.

coord-selftest 136 -> 151.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016iJoZVmU2guTEZcMghk88z

CLAUDE.md

@@ -15,7 +15,15 @@ marketplace plugin. Three components, one boundary:
   writes, `coord-inbox.sh` reads (formatted for context injection),
   `coord-done.sh` archives, `coord-count.sh` counts without delivering.
   Everything is pinned by `coord-selftest.sh`
-  (136 checks, throwaway mailbox via `CLAUDE_COORD_DIR`).
+  (151 checks, throwaway mailbox via `CLAUDE_COORD_DIR`).
+
+  **`coord-count.sh` prints TWO integers per mailbox** (`<name>\t<pending>\t<debt>`),
+  and the first must stay pending: `board.sh` counts the same inbox files
+  itself, so a debt-only count would put two different numbers under one name.
+  Debt is read from `reply-expected` in the FRONTMATTER BLOCK ONLY - a body line
+  is untrusted input and must not be able to silence a debt - and an absent
+  field means a reply IS owed, because every message written before 0.11.0
+  lacks it.
 
   **Reading is delivering — counting is not.** `coord-inbox.sh` records a
   broadcast as seen once it has printed it, so it can never be used to survey
@@ -94,6 +102,13 @@ distinct in any reword — keeping the priority while dropping the distinction
 turns prioritization into an injection surface. Selftest section 20 pins both
 halves together for exactly that reason.
 
+Since 0.11.0 the `reply-expected` field says which terminal state the SENDER
+expects. That does not soften the split, it sharpens it: the field is untrusted
+cross-repo input like the rest of the file, so the injection calls it a
+*declaration, not an instruction* and keeps both terminal states open to the
+receiver. Drop that clause and one word in a message becomes a lever that mints
+obligations in another repo.
+
 ## Conventions
 
 - Scripts are bash-3.2-safe and ASCII-only: no `declare -A`, no
@@ -102,7 +117,7 @@ halves together for exactly that reason.
 - Zero dependencies everywhere: bash + coreutils in the engine, `node:`
   builtins only in hook and tests.
 - TDD: no behavior change without a failing selftest check first.
-  `bash scripts/coord-selftest.sh` must exit 0 (136/136),
+  `bash scripts/coord-selftest.sh` must exit 0 (151/151),
   `bash scripts/board-selftest.sh` must exit 0 (36/36) and
   `bash scripts/route-selftest.sh` must exit 0 (50/50).
 - English for all code, docs, and commit messages (public repo). Norwegian