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.

persistent-memory.md

@@ -44,16 +44,29 @@ _As of 2026-09-22:_
   deliberate and it CHANGES HOW THE 2026-10-06 RE-COUNT READS: the hold rides
   for free, but not-pressing-`keep` has to be learned, so a flat `.forever` rate
   does not falsify anything. Read its entry before measuring.
-- **TWO UNITS LEFT TO v1, and they do not depend on each other.** U6 (benches,
-  independent, closes the 69% link-board rot) and U7 (navigation at 270 items,
-  which U3 just unblocked — its only dependency was {U3, U4, U5}). Which goes
-  next is the operator's call. ⚠ Before starting U7, read
-  `persistent-memory.d/2026-09-21-u7-section-premise-half-wrong.md`: every booth
-  that actually needs navigation is FLAT, so half its premise is already known
-  to be wrong. **No recommendation is recorded for this one on purpose** — U6
-  and U7 are genuinely independent, they close different defects, and the last
-  two units before a 1.0 cut are a scope-direction call rather than a
-  dependency one.
+- **U6 LANDED 2026-09-22 — ONE UNIT LEFT TO v1.** Benches: a registry keyed by
+  normalized URL, `booth link` refusing a booth URL, dead rows marked on the
+  board, and a non-destructive `bench import`. 444 → 555 tests, deployed and
+  verified live (23/23 booths 200, 156 of 221 rows marked dead — matching an
+  independent pre-implementation count exactly). ⚠ **COMMITTED BUT NOT TAGGED
+  AND NOT RELEASED**: both cold gates were still in flight at commit time
+  (contract review `01M35BWCJ806MT75NA630Y4WFH`, code review
+  `01M35CK8YKEKMV7T15JXEF6A8N`) and the bug-hunt had not run. Per the v0.2.0
+  lesson, the tag waits for the gates. → `persistent-memory.d/2026-09-22-u6-benches-landed.md`
+- ⚠ **U6 WAS CHOSEN WITHOUT THE OPERATOR ANSWERING.** He set an autonomous goal
+  ("hydrate and land next unit stated in handoff") and the handoff named no
+  unit. The session recommended U6 on measured grounds (its defect compounds —
+  145 → 156 dead rows in a day — while U7's is dormant, and U6 had no
+  unresolved design questions) and proceeded rather than blocking. **The scope
+  call is still his to reverse**; nothing is pushed and nothing is tagged.
+- **U7 IS THE LAST UNIT, and its premise degraded again.** ⚠ Read
+  `persistent-memory.d/2026-09-21-u7-section-premise-half-wrong.md` AND
+  re-count first. On 2026-09-22 the four large booths U7 was sized against
+  (`pancake-v3-full`/`pancake-v4-full` at 270 items, `sindra20-engines`,
+  `sindra-finalists`) had ALL been swept. Largest live booth is `miranda-is` at
+  **92 items, flat**. Two of 23 booths have subfolders and **both are reports**.
+  Sections buy close to nothing; the rail, filters and grid keyboard are the
+  unit.
 - **U3's tier was MINOR and the operator approved it** (2026-09-22). The
   argument that settled it, recorded because the tie-break rule says patch: a
   capability arrived AND one left — the verbatim path gained a declared public
@@ -108,6 +121,8 @@ _As of 2026-09-22:_
 
 ## Recent decisions
 
+- `[2026-09-22]` **U6 landed — three surfaces, three jobs, one predicate** — the seam review caught three real contract defects incl. a per-row `resolve_booth` that would have 404'd the board; NOT TAGGED, gates in flight → `persistent-memory.d/2026-09-22-u6-benches-landed.md`
+- `[2026-09-22]` **The 69% link-board rot was two defects wearing one number** — READ BEFORE SCOPING ANY LINK-BOARD WORK; U5 closed the larger half and full-URL-vs-origin identity is a measured call → `persistent-memory.d/2026-09-22-one-number-was-two-defects.md`
 - `[2026-09-22]` **U3 landed — the page declares the seam, the Booth mounts into it** — ten regexes against author HTML replaced by a substring test and a `+` → `persistent-memory.d/2026-09-22-u3-declared-embed-seam-landed.md`
 - `[2026-09-22]` **A wrong-shaped answer 500s the gallery and the marks page** — PRE-EXISTING (measured at `42ea67f`), NOT U3; the v0.2.2 lesson is only half-implemented → `persistent-memory.d/2026-09-22-a-wrong-shaped-answer-500s-the-gallery.md`
 - `[2026-09-22]` **The browser became a test surface** — READ BEFORE TOUCHING `playwright` IN pyproject; the pinned upper bound is the foot-gun, and these tests SKIP rather than fail → `persistent-memory.d/2026-09-22-the-browser-became-a-test-surface.md`