feat(route): give next-cost a writer, and make the rubric the only copy

The board line's next-cost field had a reader (board.sh) and no writer, so
its value was retyped by hand every session and drifted into several
competing spellings. Cleaning the data could not fix that: the cause was the
missing write path.

route.sh is that writer. Four scored traits of the next task -- path,
verification, reversibility, scope -- plus a required rationale, run through
the operator's model rubric moved here as the single copy. The row table is a
closed set of six values, so a seventh spelling cannot enter circulation, and
route-selftest.sh section 6 runs the round trip (route emits -> board parses)
inside one repo rather than across two.

Two spellings of one decision come out of one table: the rubric name for the
board line, the CLI alias for the command the operator pastes. Effort levels
are the set pinned in this marketplace; model aliases are gated against the
installed claude rather than hardcoded.

Three things worth naming:

- Escalation is asymmetric. Any single trait escalates; the cheapest row needs
  all four at the cheap end. Underkill costs one session, overkill costs quota
  every session -- but a wrong architecture call costs more than either.
- The Fable rows fire only from an explicit judgement flag, never inferred
  from the last-session record. "The session did not finish" also covers
  context exhaustion and operator interrupts, which say nothing about the
  model, and Fable runs without an advisor.
- The trait block is a single-line HTML comment because board.sh's NESTE
  extractor skips only lines that START with '<!--'. Measured first: a YAML
  block or a multi-line comment silently replaces the repo's next step on the
  board with "next_task:". Pinned by section 7.

board.sh is untouched as a program; its header now points at route.sh for the
value set so this does not reopen the two-specs defect 305f168 closed.

Selftests: coord 136, board 30, route 47 (new), node 7.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017peNgsxVt1BR4BTuMwiPoX

CLAUDE.md

@@ -40,10 +40,35 @@ marketplace plugin. Three components, one boundary:
   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
+- **Route (`scripts/route.sh`):** pure calculator for the next session's model
+  and effort. Takes four scored traits of the next task plus a required
+  rationale, and prints one block of `key=value` lines: the rubric row, the rule
+  that fired, the `next-cost` value, a pasteable startup command, the one-row
+  cheaper fallback, and the STATE.md comment lines. Pinned by
+  `route-selftest.sh` (47 checks).
+
+  **It is here because it is the WRITER for the field `board.sh` already reads.**
+  `next-cost` had a reader and no writer, so it was hand-typed every session and
+  drifted into several competing spellings — cleaning the data
+  could not fix that, because the cause was the missing write path. The row
+  table is a closed set of six values, so a seventh cannot enter circulation,
+  and section 6 of the selftest runs the round trip (route emits → board parses)
+  *inside* one repo rather than across two. `board.sh` itself is untouched: a
+  calculator that prints to stdout writes nothing, and the session writes
+  STATE.md.
+
+  **The row table is the operator's global rubric, moved here as the single
+  copy.** It is not a second spec — `board.sh --help` documents the board line's
+  *grammar* and points here for the *values*. Scoring the traits is judgement
+  and belongs to the skill; turning scores into a row is a lookup and takes zero
+  model calls.
+- **Skills (`skills/coord-send/`, `skills/board/`, `skills/route/`):** 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.
+  since `board.sh` deliberately prints evidence and takes no position. `route`
+  likewise owns the *scoring*: the calculator is deterministic, so all judgement
+  sits in choosing the four trait values, and the skill must never reason its
+  way to a model instead.
 
 **Boundary rule:** the mailbox is transport, not state. Durable decisions
 live in the owning repo's docs/git history; messages are notices pointing at
@@ -77,24 +102,27 @@ 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) and
-  `bash scripts/board-selftest.sh` must exit 0 (30/30).
+  `bash scripts/coord-selftest.sh` must exit 0 (136/136),
+  `bash scripts/board-selftest.sh` must exit 0 (30/30) and
+  `bash scripts/route-selftest.sh` must exit 0 (47/47).
 - 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` and `bash scripts/board-selftest.sh`
-  (or `npm test`, the Node wrapper around both)
+- Test: `bash scripts/coord-selftest.sh`, `bash scripts/board-selftest.sh` and
+  `bash scripts/route-selftest.sh` (or `npm test`, the Node wrapper around all three)
 - 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)
+- Route smoke test: `bash scripts/route.sh --path known --verification strong
+  --reversibility cheap --scope local --rationale x` (writes nothing, instant)
 
 ## Release
 
 Version must agree across: `.claude-plugin/plugin.json`, `package.json`,
-README version badge, `skills/coord-send/SKILL.md` and `skills/board/SKILL.md`
-frontmatter, git tag `vX.Y.Z`, and the catalog `ref` in
+README version badge, `skills/coord-send/SKILL.md`, `skills/board/SKILL.md` and
+`skills/route/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);