feat(board): cross-repo attention board as script + skill (0.9.0)

The mailbox answers "who wrote to me"; it never answered "which repo
deserves the next session". board.sh scans every discovered repo and reads
three sources each: the STATE.md next-step block with its optional board
line, git status, and that repo's pending mailbox count. Read-only by
construction, pinned by board-selftest.sh (28 checks).

It ships here rather than as a personal script because the mailbox is one
of its three inputs and the two carry the same axis distinction: a pending
count means others are waiting on that repo, while who a repo waits ON comes
only from its board line, since the message format has no reply-to field.
Splitting the board from the mailbox would put that distinction in two
places. It also lets the skill resolve the engine through CLAUDE_PLUGIN_ROOT
like every other script here, instead of depending on a file that exists
only in ~/.claude/scripts (a directory with no remote and no backup).

The skill is a ranking, not a report: re-runs the board every invocation
because counts drift, ranks by what unblocks the most and what is cheapest
to move, then names one repo, the rule that fired, and the real next action
read from that repo's STATE.md. Never the table. Not wired into session
start, which would spend context on repos the session is not in.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MubwdTi88yu4hVLAFG1LbM

CLAUDE.md

@@ -28,8 +28,22 @@ marketplace plugin. Three components, one boundary:
   wrapper (marketplace convention: hooks are `.mjs`) that calls
   `coord-inbox.sh` and emits the `hookSpecificOutput.additionalContext`
   envelope. No mailbox logic lives here. Always exits 0.
-- **Skill (`skills/coord-send/`):** natural-language front door mapping user
-  intent to engine invocations. No mailbox logic lives here either.
+- **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` (28 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
+  are waiting on this repo*; who a repo waits *on* comes only from its board
+  line, because the message format has no reply-to field. Enforcing that in one
+  of two repos would not be enforcing it. `~/.claude/scripts/board.sh` is a
+  deployed copy (the operator's `board()` shell function points at it), exactly
+  as with the `coord-*` scripts — this repo is the source of truth.
+- **Skills (`skills/coord-send/`, `skills/board/`):** natural-language front
+  doors mapping user intent to engine invocations. No mailbox logic lives here
+  either. `board` additionally owns the *ranking* — which repo wins and why —
+  since `board.sh` deliberately prints evidence and takes no position.
 
 **Boundary rule:** the mailbox is transport, not state. Durable decisions
 live in the owning repo's docs/git history; messages are notices pointing at
@@ -63,21 +77,24 @@ 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 (136/136) and
+  `bash scripts/board-selftest.sh` must exit 0 (28/28).
 - English for all code, docs, and commit messages (public repo). Norwegian
   trigger aliases in the skill description are deliberate.
 - Conventional Commits: `type(scope): description`.
 
 ## Commands
 
-- Test: `bash scripts/coord-selftest.sh` (or `npm test`, the Node wrapper)
+- Test: `bash scripts/coord-selftest.sh` and `bash scripts/board-selftest.sh`
+  (or `npm test`, the Node wrapper around both)
 - Hook smoke test: `node hooks/scripts/session-start.mjs` (expects JSON on stdout)
+- Board smoke test: `bash scripts/board.sh` (read-only, ~3s over the real tree)
 
 ## Release
 
 Version must agree across: `.claude-plugin/plugin.json`, `package.json`,
-README version badge, `skills/coord-send/SKILL.md` frontmatter, git tag
-`vX.Y.Z`, and the catalog `ref` in
+README version badge, `skills/coord-send/SKILL.md` and `skills/board/SKILL.md`
+frontmatter, git tag `vX.Y.Z`, and the catalog `ref` in
 `ktg-plugin-marketplace/catalog/.claude-plugin/marketplace.json`. Release via
 the catalog's `scripts/release-plugin.mjs repo-mailbox` (tag + ref bump
 together);