feat(u6): benches — a registry with identity, and the rule enforced

The standing link board carried three jobs because only one of them had a
surface. Re-measured before contracting, its 221 rows split into 178 booth
announcements (156 already dead) and 43 non-booth rows, of which 8 are the same
bench re-posted. U5 gave the booth announcement a home; this gives the running
service one, and refuses the one shape that now has somewhere better to go.

- booth/benches.py (new, stdlib-only and sibling-free): the Bench record, URL
  normalization as the identity, a lenient read on the render path and a strict
  read on the write path, atomic replace under an flock, and a stated total
  order (state rank, name casefolded, id).
- links.booth_target: ONE predicate for "is this a booth URL", consumed by the
  CLI refusal, the board's dead marker and bench import. Host-agnostic,
  path-shaped, percent-decoded, never raises.
- booth link refuses a booth URL, names `booth new --why`, and writes nothing —
  not the row, not the board directory, not the announcement.
- The board marks rows whose booth has been swept. Nothing here deletes a row:
  removal stays the operator's two clicks through the existing bulk control.
- booth bench add|ls|state|rm|import. import writes nothing without --apply and
  never edits links.md.
- docs/archive/links-2026-09-22.md: the board archived verbatim into git.

Identity is the FULL normalized URL, not the origin, and that was measured:
origin identity collapses the 43 non-booth rows to 19 groups by merging eight
distinct gitea repositories into one row, three unrelated HuggingFace model
cards into one, and the two LRPG surfaces on 10.100.10.50:8321 — the design
doc's own example of two real benches — into one. Full-URL identity still
collapses both cases that doc names: talk 5 to 1, Peedlar 3 to 1.

booth link is NOT deprecated. Roughly 14 of the 35 distinct non-booth targets
are reference bookmarks for which the board is the right and only home; the
design doc's plan to deprecate it would have evicted a third of its live
content. Corrected there, along with what "normalized URL" means.

The seam review found three real defects in the contract before any code: the
claim that test_stdlib_only already forbids sibling imports (it exempts `booth`
on purpose), naming resolve_booth as the dead marker's existence check (it
raises HTTPException(404), so one swept booth would have 404'd the whole board
page), and silence on percent-encoding (booth links are emitted through
quote(name, safe=""), so a raw comparison marks every encoded booth dead
forever). That both list_booths and sweep_once skip the registry was verified
against the real functions rather than assumed.

444 -> 555 tests. Deployed and verified live: 23/23 booths 200, and the board
renders 156 dead of 221 rows, matching an independent pre-implementation count.

NOT TAGGED: both cold gates are in flight (contract review
01M35BWCJ806MT75NA630Y4WFH, code review 01M35CK8YKEKMV7T15JXEF6A8N) and the
bug-hunt has not run. Per the v0.2.0 lesson, the tag waits for the gates.

ROADMAP.md

@@ -1,7 +1,7 @@
 # The Booth — roadmap
 
 Design: [`docs/design/information-architecture.md`](docs/design/information-architecture.md).
-Current version: `0.5.0` (U1, U2, U3, U4 and U5 landed; extracted from eshpfi 2026-09-21).
+Current version: `0.5.0` (U1 through U6 landed; extracted from eshpfi 2026-09-21).
 
 ## v1 target
 
@@ -15,17 +15,27 @@ defect — not a wish. The measurements are in the IA doc.
 | 3 | ~~**Declared embed seam**~~ — **landed `87e2c53`, released `v0.5.0`** | 6 regexes injected into arbitrary author HTML, load-bearing for asks | U3 |
 | 4 | ~~**Derived lifetime**~~ — **landed `c3a97c1`, released `v0.4.0`** | 70% of booths on the `.forever` escape hatch (54% when first counted) | U4 |
 | 5 | ~~**Self-announcing booths**~~ — **landed `c015a91`, released `v0.3.0`** | job 5 had no home, so it lived on the link board as 145 dead rows | U5 |
-| 6 | **Benches** — registry, identity, enforced rule, migration | 69% link-board rot; the same bench posted 5× | U6 |
+| 6 | ~~**Benches**~~ — registry, identity, enforced rule, migration | 69% link-board rot; the same bench posted 5× | U6 |
 | 7 | **Navigation at 270 items** — sections, rail, filters, grid keyboard | one flat wall; subfolder structure discarded at render | U7 |
 
 Ordering is dependency-driven, not priority-driven: **U1 → U2 → {U3, U4, U5} →
 U7**, with **U6 independent** of all of them (different storage, different
 surface) and therefore the safest thing to land first or in parallel.
 
-**U1, U2, U3, U4 and U5 are landed — the whole middle tier is closed.** U6
-remains independent and unstarted; **U7 is now unblocked**, since its only
-dependency was `{U3, U4, U5}`. Two units left to v1, and they do not depend on
-each other, so either can go next.
+**U1 through U6 are landed.** **U7 is the last unit before the 1.0 cut** — its
+only dependency was `{U3, U4, U5}` and that closed with U3.
+
+⚠ **Before starting U7, read
+`persistent-memory.d/2026-09-21-u7-section-premise-half-wrong.md`, and re-count
+the booths first.** Half its premise is already known to be wrong — every booth
+that actually needs navigation is FLAT — and the booth set churned again on
+2026-09-22: the four large booths U7 was sized against (`pancake-v3-full` and
+`pancake-v4-full` at 270 items, `sindra20-engines`, `sindra-finalists`) have all
+been swept. The largest live booth is now `miranda-is` at 92 items, flat. Two of
+23 booths have subfolders (`pewpew-ui-brief`, `dfa-concepts`) and **both are
+reports** — the job where grid navigation matters least. Sections, one of U7's
+four named components, buys close to nothing. The rail, the filters and the grid
+keyboard are the unit.
 
 **U5's adoption is a measured prediction, not a finished result**, and it is
 TWO predictions rather than one. The operator declined a fleetwide announcement
@@ -75,6 +85,8 @@ Where it already binds, and what the rule is in each case:
 | legacy ask import | `(mtime, name)`, which is the order `list_asks` gave them |
 | link board rows | pinned first, then newest-first |
 | a booth's announcement | not a collection — one flat record per booth, nothing to order (U5) |
+| the bench registry | `(state rank, name casefolded, id)` — live before promoted before retired, then alphabetical, with the id as a TOTAL tie-break so two benches sharing a name cannot swap (U6) |
+| the link board's dead marker | not an order — a per-row stamp read from the existing `order_for_display` sequence, so marking cannot move a row (U6) |
 | embed anchors in a verbatim report | **document order** — what `querySelectorAll` yields, so the author's markup decides (U3) |
 | the embed tail (fragments the author did not place) | **payload order**, which is the marks order `(created, id)` — one rule, whether a fragment lands at an anchor or at the end (U3) |
 | questions within a pick | declaration order, in the payload's `questions` LIST — carried by the format rather than by object-key insertion order (U3) |
@@ -92,7 +104,9 @@ ordering: one rule, one place, every surface reading it.
 Where it is still to be decided, and must be before the unit ships: **U7's
 section ordering and its compare pairing** (sections need a stated order among
 themselves, not just within; pairing by filename needs a rule for what happens
-to an unpaired file), and **U6's bench listing**.
+to an unpaired file). **U6's bench listing is settled** — the row above.
+Compare pairing is parked to v1.1 with compare mode itself, so U7 carries one
+undecided rule, not two.
 
 The test for any new ordered surface: *can you write the rule down in one line?*
 If not, it does not have one yet.