enhance(#3873): the STATE.md schema — one owner, generated artifacts (#3880)

* test(#3873): failing-first locale parity, plus tripwires for what must not move

Pins ADR-3473 §8.8 at the artifact a reader actually sees. The English STATE.md
reference carries a Status lifecycle section that is missing from all four
translations — the section documenting the status enum whose clobbering is
#3853. The test derives the heading set rather than hard-coding the missing
one, and names the locale and the heading when it fails.

Two tripwires that must pass today and after. The field-drift guard still
catches a re-derived fallback ladder: §8.8 instructs deleting that script, and
that instruction rests on a wrong premise about what it guards, so the test
stops a future reader from deleting it on the ADR's word. And last_activity's
label resolution is pinned to what ships today, because it is declared in one
of the two tables this phase consolidates and not the other — the
consolidation must not silently pick a side.

The locale test buckets under docs rather than state, which is what it tests;
that bucket is allowlisted with justification rather than folded into an
unrelated docs suite. It reads only markdown, so it carries no allow-test-rule
marker — a marker there would suppress nothing and would grow the unverified
pool against its ceiling.

Refs #3873

* feat(#3873): one schema owns the STATE.md key set, three tables become projections

ADR-3473 §8.8. The key set was declared in four places that had to agree by
hand and already did not: FIELD_CLASSIFICATION, FRONTMATTER_BODY_SOURCE,
FRONTMATTER_KEY_TO_BODY_LABEL and buildStateFrontmatter's emit behavior. One
frozen null-prototype schema now declares each key's type, enum, cardinality,
source, preservation, body source, body label, accepted parse shapes and
whether it is emitted unconditionally; the three tables are derived from it at
module load.

The projections are byte-identical to the literals they replace, key order
included, and the parity tests compare against verbatim copies of today's
tables rather than re-deriving both sides from the schema — a parity test fed
from one source proves nothing, which is how a consolidation ships a changed
policy under a green test.

last_activity was the live disagreement: present in one table, absent from the
other. The schema declares what ships today rather than the tidier answer, and
a test pins it.

The schema is a leaf module and owns the four field-policy types, re-exported
from state-transition so existing importers are untouched — the same split
health-diagnostic-types made to break a CJS require cycle.

Refs #3873

* feat(#3873): generate the schema-derived regions, parity-check the prose tables

ADR-3473 §8.8's generator half. gen-state-md-docs.cjs owns marked regions in
the shipped template and all five reference docs, follows gen-features.cjs's
fail-closed contract, and is wired into regen:derived and lint:generated-sync.

The Status lifecycle section was missing from all four translations — the
section documenting the status enum behind #3853 — and is now generated into
every locale. Field cardinality is a new generated table: pure schema data,
no prose, so nothing to lose.

The Field-reference and Status-values tables are parity-CHECKED rather than
generated. Their Purpose, When-populated and Matched-text columns are
genuinely hand-translated per locale, and §8.8 itself says prose stays
hand-translated; generating them from an English registry would overwrite four
locales' translations on every write. The row set is checked against the schema
instead, so a key added to one and not the other fails, which is what field
drift actually means. Building that check found last_activity_desc
undocumented in all five tables.

Three keys the docs describe are absent from the schema — active_phase,
next_action, next_phases. They are grandfathered by name, not by wildcard, so a
fourth fails: a declared gap with a forcing function rather than a silent one.

Refs #3873

* fix(#3873): declare what the parsers do, and close the shape-parity gap

Two declarations in the new schema described intended behavior rather than
actual — the defect class this epic exists to end, committed inside the epic.
Both were caught by executing the parsers instead of reading their docstrings.

current_plan.acceptedShapes claimed ['N', 'N of M']. Standalone, the hybrid
shape errors; the path that looks like support is parseInt truncating '2 of 5'
to 2 and discarding the rest. Narrowed to ['N']. The parser is deliberately NOT
fixed here: that is #3784 and PR #3791 is already doing it. When #3791 lands
this row must widen, and the shape test will go red until it does — the schema
and the parser cannot drift apart quietly, which is what §8.8's checked-not-
generated rule is for.

STATUS_LIFECYCLE_ENUM claimed to be the closed set status can hold.
normalizeStateStatus passes unrecognized prose through unchanged, so it is not
closed at runtime. The seven members are the canonical values it maps onto; the
docstring now says that and the test asserts the real lenient contract.

Closes the acceptance item that a test asserts the parsers accept exactly the
declared shapes: the check is table-driven over every row carrying
acceptedShapes, guarded against passing vacuously on an empty set, and fails
loudly if a future row has no registered driver. Adds the unwired-label throw
and the fast-check property that every projection agrees with its schema row.

Refs #3873

* fix(#3873): keep the shipped template's frontmatter first, and make row 27 able to fail

The remote matrix caught 12 failures with one cause. Making the template's
frontmatter a generated region wrapped it in its own yaml fence ahead of the
markdown fence, so extractFileTemplate and readShippedStateTemplateBody — which
both match the single markdown block — found the heading first, not the
frontmatter. That breaks the contract every new project's STATE.md is created
from: bug #21 and epic #1969 B8 pin that the File Template block starts with
frontmatter and carries gsd_state_version.

The markers now sit inside the single markdown fence, so the fence opens before
the frontmatter and the region still ends ahead of the heading. Same layout as
before this phase, with markers embedded rather than a second fence.

Row 27 existed to catch exactly this and did not, because it was writer-seeded:
it asserted against the generator's own output shape, so it passed on the broken
template. It now parses the fence the way production does and was verified to
fail against the broken shape before being trusted against the fixed one. A test
that would not have caught the bug it exists to prevent is worse than no test.

The emitted-attribution failure was separate and the fragment was the wrong
remedy: gsd-core/templates/state.md self-attributes under a verbatim-copy
identity rule, so a diff touching it needs no acknowledgment. Fragment deleted
rather than left explaining nothing.

Refs #3873

* docs(#3873): how to change the STATE.md schema

The phase gate was right and my docs artifact was wrong. I listed
lint:generated-sync as the second enablement step, which is a verification
command dressed as one, and then claimed a one-step sequence owed no how-to.

The real sequence is build:lib then regen:derived, and the ordering is a trap:
the generator reads the COMPILED schema, so regenerating before building
regenerates against the previous schema and commits artifacts that look
plausible while disagreeing with the code just written. A reference table
cannot carry an ordering dependency; that is what the how-to test is for.

The page covers adding, changing and removing a key, every reason code the
check emits and what to do about each, what is generated versus hand-translated
and why the two prose-bearing tables are parity-checked instead of generated,
adding a language, and the three grandfathered keys. Indexed from docs/README.md.

Refs #3873

* chore(#3873): backfill changeset PR number

---------

Co-authored-by: sim <sim@local>

docs/adr/3473-enforcement-by-construction.md

@@ -240,7 +240,13 @@ Both close #3349 and #3360, which are **read-side** defects a real parser fixes
 
 **Rule — parsers are checked, not generated.** Parse functions stay hand-written. A test asserts they accept **exactly** the shapes the schema declares — no more, no fewer. Generating a parser is a substrate decision this epic does not take; the shape-proliferation family (#3784's three spellings of "plan N of M") is closed by declaring the accepted set, not by emitting the matcher.
 
-**Consequence for the guard.** `scripts/lint-state-field-drift.cjs` (805 lines) is **deleted** in the same PR. Field drift between the table, the template and the docs stops being detectable because it stops being representable.
+**Consequence for the guard.** Field drift between the schema, the template and the docs stops being *representable*, because the artifacts are generated from the schema and a drift check refuses a stale one.
+
+> **Amendment, 2026-08-26 (Phase 3, #3873) — this paragraph originally instructed deleting `scripts/lint-state-field-drift.cjs` (805 lines) on the grounds that it detected that drift. Verified against `next`: it does not, and never did.** That script's own header declares it the drift guard for the **STATE.md field-extraction fallback chain** — epic #3180, issue #3187, ADR-3180 Decision 4 §7.7. It detects re-derivations of the *"prefer the frontmatter scalar, else fall back to the body field"* coercion ladder across `src/**` and the prompt layer. It contains no reference to `FIELD_CLASSIFICATION`, to the template, or to the reference docs. Nor does any **other** script own field/template/docs drift — the full `scripts/` inventory carries none. The instruction named a guard surface that did not exist.
+>
+> **The guard is therefore retained**, and `tests/lint-state-field-drift-retained.test.cjs` pins that decision so a future reader does not delete it on this ADR's earlier word. A key-set schema makes a *key-set disagreement* unrepresentable; it does nothing about a *code-shape* re-derivation of a coercion ladder. Those are orthogonal, and Decision 6 sanctions retiring a guard the change makes **redundant** — which this one is not.
+>
+> **This is the second guard-retirement claim in this ADR to rest on a wrong premise**, after §8.6's (see its own amendment). Both described a guard surface their author believed existed. The pattern is worth naming: a retirement claim in this ADR is a *hypothesis about a guard's contents*, and Decision 6's ledger requirement should be read as obliging the implementing phase to verify that hypothesis before acting on it — not merely to count the result.
 
 #### 8.9 Each subsumed child is driven fail-first — *Required — every phase*
 
@@ -261,8 +267,9 @@ Both close #3349 and #3360, which are **read-side** defects a real parser fixes
 
 | Phase | Guard | Δ |
 |---|---|---|
-| 1 (§8.6) | `lint-state-write-path-drift.cjs` — two `sanctioned-permanent` baseline entries retired; raw-write check retained | shrinks |
-| 3 (§8.8) | `lint-state-field-drift.cjs` — **deleted** | **−805 lines, −1 guard** |
+| 1 (§8.6) | `lint-state-write-path-drift.cjs` — seam-bypass `writeStateMd(` arm and its whole ratchet apparatus retired, baseline file deleted; composition-bypass arm retained and made terminal; raw-write check **added net-new** | **−665 lines, −1 file, +1 check** — net shrink |
+| 2 (§8.7) | none — the reporting diff makes no guard redundant | **0**, stated rather than omitted |
+| 3 (§8.8) | `lint-state-field-drift.cjs` — **retained**, see §8.8's amendment; a generated-artifact drift check and a locale-parity check are **added** | **+2 checks, 0 retired — this phase GROWS** |
 | — | `lint-planning-snapshot-bypass-drift.cjs` — extended to the write side by ADR-3180 Amendment 8 | **growth, declared** |
 
 Net across the set: one guard retired, one increase recorded honestly. The increase belongs to a concurrent lane under a different ADR and is listed here so the accounting is complete rather than flattering.
@@ -297,7 +304,7 @@ Net across the set: one guard retired, one increase recorded honestly. The incre
 | Guard | Status under this ADR |
 |---|---|
 | `scripts/lint-state-write-path-drift.cjs` | retained, shrunk (§8.6) — seam-bypass `writeStateMd(` arm and its ratchet retired at Phase 1; composition-bypass arm retained and made terminal; raw-write check added net-new. See §8.6's amendment. |
-| `scripts/lint-state-field-drift.cjs` | **retired at Phase 3** (§8.8) |
+| `scripts/lint-state-field-drift.cjs` | **RETAINED** — the Phase-3 retirement instruction rested on a wrong premise about what this guard does; see §8.8's amendment. It guards the ADR-3180 §7.7 / #3187 coercion ladder, which no schema makes unrepresentable. |
 | `scripts/lint-vendored-deps.cjs` | reused as-is for §8.1's vendoring rule |
 | `local/no-external-require-in-bin` | reused as-is; enforces §8.1's packaging rule |
 | `local/no-adhoc-markdown-parsing` | widened past `src/**/*.cts` per Decision 5 (coverage fix, tracked on #3426/#3239) |