fix(state-line-guard): Edit path used String.replace, not a function

current.replace(oldStr, newStr) with newStr as a STRING lets JS treat
$-sequences inside it ($&, $`, $', $$, $n) as special replacement
patterns, even though oldStr (the search side) is a plain string. A
new_string documenting old backtick-substitution style ($`cmd`) - the
kind of prose a STATE.md shell-conventions section writes routinely -
triggers it. Measured against the real bug (.claude/STATE.md,
2026-08-15): a 5-line addition on a 112-line file projected to 219
lines and was wrongly denied.

Fix: current.replace(oldStr, () => newStr) - a function replacement is
never pattern-substituted, covering every $-sequence at once. The
replace_all branch (split/join) was never affected.

Direction was always fail-closed (over-blocks, never under-blocks a
real oversize), but it made exactly the STATE.md files that document
shell conventions hard to edit via Edit.

state-line-guard-selftest.sh: 23/23 (+2, section 9: $` as the repro,
$& as a second sequence proving the fix is general).

Also updates CLAUDE.md's pinned selftest counts (197/178/69/21 were
already stale before this session's own additions; now 206/183/69/23).

CLAUDE.md

@@ -16,7 +16,19 @@ marketplace plugin. Three components, one boundary:
   `coord-done.sh` archives, `coord-count.sh` counts without delivering,
   `coord-sweep.sh` closes the aged FYI backlog machine-wide.
   Everything is pinned by `coord-selftest.sh`
-  (197 checks, throwaway mailbox via `CLAUDE_COORD_DIR`).
+  (206 checks, throwaway mailbox via `CLAUDE_COORD_DIR`).
+
+  **`ktg-plugin-marketplace` is a RETIRED `--to` address (operator decision
+  2026-08-15), rejected rather than redirected.** It is a polyrepo directory,
+  not a git repo, so `basename(git toplevel)` can never resolve to it and no
+  session was ever able to hold that identity naturally - mail for it belongs
+  to `catalog` instead. A silent redirect was considered and declined: it
+  delivers mail somewhere the sender does not believe it landed, which is the
+  same misdelivery defect this closes a second time (2 messages sat
+  undelivered 2 days on this exact misaddressing before `catalog`'s H4 count
+  caught 6 more). Rejection fails loud at the sender, at the moment the
+  mistake is made. Only `--to` is retired, not `--from` - the defect was mail
+  *arriving* there, never mail claiming to *originate* there.
 
   **`coord-sweep.sh` is the only path that closes a message with no human in
   the loop, and every constraint on it follows from that.** It may close exactly
@@ -120,10 +132,29 @@ marketplace plugin. Three components, one boundary:
   not the current threshold, and are left as-is rather than rewritten.
   `session-start.mjs`'s 160-line injection window still covers the new
   120-line limit with room to spare, so no change was needed there.
+
+  **The Edit path's `current.replace(oldStr, newStr)` was a dollar-pattern
+  injection bug, found and fixed 2026-08-15.** Passing `newStr` as a STRING
+  makes JavaScript interpret `$`-sequences inside it ($&, `` $` ``, `$'`,
+  `$$`, `$n`) as special replacement patterns, even though `oldStr` (the
+  search side) is a plain string, not a RegExp. A `new_string` documenting
+  old backtick-substitution style (`` $`cmd` ``) - exactly the prose a
+  STATE.md's shell-conventions section writes routinely - triggers it.
+  Measured against the real bug (`.claude/STATE.md`): a 5-line addition on a
+  112-line file projected to 219 lines and was wrongly denied. Direction is
+  always fail-CLOSED (never fail-open: it can only over-block, never
+  under-block a real oversize), but it made exactly the kind of STATE.md
+  that documents shell conventions hard to edit. Fix: replace with a
+  function, `current.replace(oldStr, () => newStr)` - a function result is
+  never pattern-substituted, so this covers every `$`-sequence at once, not
+  a `` $` ``-specific escape. The `replace_all` branch (`split`/`join`) was
+  never affected - `join` does not interpret its argument as a pattern.
+  Pinned by state-line-guard-selftest.sh section 9 (`$\`` as the real repro,
+  `$&` as a second sequence proving the fix is general).
 - **Board (`scripts/board.sh`):** cross-repo attention board. Reads STATE.md
   next-step blocks + board lines, `git status`, and mailbox pending counts, and
   prints one line per repo. Read-only by construction: it writes to no repo, no
-  STATE.md and no mailbox. Pinned by `board-selftest.sh` (178 checks).
+  STATE.md and no mailbox. Pinned by `board-selftest.sh` (183 checks).
 
   **It lives here because the mailbox is one of its three inputs, and it carries
   the same axis distinction the mailbox does.** A pending count means *others
@@ -429,10 +460,10 @@ obligations in another repo.
 - 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 (197/197),
-  `bash scripts/board-selftest.sh` must exit 0 (178/178),
+  `bash scripts/coord-selftest.sh` must exit 0 (206/206),
+  `bash scripts/board-selftest.sh` must exit 0 (183/183),
   `bash scripts/route-selftest.sh` must exit 0 (69/69) and
-  `bash scripts/state-line-guard-selftest.sh` must exit 0 (21/21).
+  `bash scripts/state-line-guard-selftest.sh` must exit 0 (23/23).
 - English for all code, docs, and commit messages (public repo). Norwegian
   trigger aliases in the skill description are deliberate.
 - Conventional Commits: `type(scope): description`.