docs(adr): ADR-0178 — derive the placement index instead of maintaining it

Smell-audited: depth 3: new ADR + ADR-0033 amendment. The smell that opened
this cycle was mine, not the code's. I drafted "retire the Pattern A/B plan;
Zig is the finished form for hot paths" on the strength of two claims, and the
mandatory Devil's-advocate fork refuted both against the files:

  1. The six `ready_for_migration` rows I read as "scheduled to move count/seq/
     first into .clj, which would cost perf" are `pattern: B1` with NO
     `target_loc`. ADR-0033 D3 defines B1 as Zig-with-no-.clj — B1's finished
     form IS Zig. I attacked a straw man, and my proposed policy was already
     ADR-0033 D5 ("fast-path = Tag switch") restated.
  2. The plan was not unexecuted. D-062 was discharged 2026-05-27; set.clj /
     string.clj / walk.clj carry 12 / 21 / 11 real (def …) bodies. What rotted
     was the LEDGER, not the plan — 42 rows still read `transient_zig` for vars
     whose .clj had shipped.

I re-verified every one of those against the tree before acting on it, plus the
fork's two extra findings (two `leaf_loc` paths point at nonexistent files; the
`--list-vars` consumer the file cites has never been built). All confirmed. The
fork also blocked the F-003 seizure: retiring an unbuilt-residual placement
policy is not this cycle's to make, so no forward policy is stamped.

So the fix is not deletion and not repair-by-hand — it is derivation:

- `(cljw.internal/__dump-placement)` derives each Var's implementation home
  from its root tag (`builtin_fn` → zig, `fn_val`/`multi_fn` → clj, else value/
  unbound) plus its flags. Decided by the runtime, so it cannot be wrong.
- `scripts/gen_placement.sh` requires every bundled namespace first —
  namespaces are lazy (ADR-0163), so a bare dump under-reports — and renders
  data/placement.yaml. 49 hand-written rows became **1,326 generated ones
  across 31 namespaces**.
- `scripts/check_placement_status.sh` is now the `placement_drift` gate:
  regenerate, diff, fail. Its old body audited the completed migration.

I narrowed the fork's proposal in one place, deliberately. It asked for the
full A/B1/B2/C-thin split via an AST classifier over the .clj bodies; that
classifier must handle `(def x (fn* …))`, multi-arity fn*, macros and computed
defs, and a misclassified generated row is a NEW lie class. The root-tag axis
is reported, not inferred. An index that guesses is worse than one that
reports; the finer split rides on top when a consumer needs it (`zig-leaf`
already separates B1 from a B2 leaf).

Two things the index made visible that no document could have:

- 394 vars are Zig-implemented and **725 are Clojure-implemented**. The audit
  that opened this cycle argued from the 124.7K:8.8K LOC ratio that the Clojure
  surface was structurally thin. At the var level it is the majority. LOC was
  the wrong denominator.
- `clojure.spec.alpha` appears with 123 clj vars + 17 values. It is bundled and
  working — and the same audit recorded it as unimplemented, because
  docs/works/ladder.md and COVERAGE.md carry no row for it. A working feature
  missing from the ledgers misleads exactly like a broken one.

Smoke green (7 passed / 0 failed, corpus 4253/4253).

Author: chaploud

.claude/CLAUDE.md

@@ -588,13 +588,16 @@ zig fmt src/           # format
   C / D classification per var, special form, and host class. Read by
   test runner, REPL error message, and future `cljw --list-vars`. See
   ADR-0013 for the Tier D rationale.
-- [`placement.yaml`](../data/placement.yaml) — Clojure-ns var placement SSOT
-  (Pattern A/B + transient_zig migration status + dependencies). Read
-  by `scripts/check_placement_status.sh` (audit + status flip), future
-  `cljw --list-vars` (alongside compat_tiers.yaml), and ADR-0033
-  amendment history. Role split: compat_tiers.yaml = Java/cljw surface
-  (Class-level), placement.yaml = Clojure-ns vars (var-level). Per
-  `private/notes/clj_vs_zig_split_proposal_v5.md` §15.
+- [`placement.yaml`](../data/placement.yaml) — **GENERATED** index of where every
+  interned Var's implementation lives (`zig` / `clj` / `value` / `unbound` +
+  flags), covering every var in every bundled namespace. Produced by
+  `scripts/gen_placement.sh` from `(cljw.internal/__dump-placement)`; the
+  `placement_drift` gate regenerates and diffs it on every full gate, so it
+  cannot disagree with the code (ADR-0178). **Do not hand-edit.** Role split:
+  compat_tiers.yaml = Java/cljw surface (Class-level), placement.yaml =
+  Clojure-ns vars (var-level). Whether a var's *current* placement is its
+  *intended* one is a judgement, not a fact — that lives in `.dev/debt.yaml`
+  with a barrier (today one row, D-094). ADR-0033 D2-D5 is the placement rule.
 - [`host_interfaces.yaml`](../data/host_interfaces.yaml) — closed-set SSOT for the
   deftype/reify/extend-type host-supertype markers (`Object`, `clojure.lang.*`).
   Single in-code read point: `src/runtime/host_interface.zig`. Gated by

.dev/README.md

@@ -34,5 +34,6 @@ templates in **ROADMAP §15.2**:
 - `debt.yaml` — row-level debt ledger (ADR-0072; replaced the planned
   `known_issues.md`). The live SSOT for technical debt.
 - `data/compat_tiers.yaml` — per-namespace/class Clojure tier table.
-- `data/placement.yaml` — Clojure-ns var placement SSOT (ADR-0033; covers the planned
-  `status/vars.yaml` var tracking, which was not built).
+- `data/placement.yaml` — GENERATED per-var placement index (ADR-0178; supersedes
+  the planned `status/vars.yaml` tracking, which was never built). Regenerate with
+  `scripts/gen_placement.sh`; the `placement_drift` gate keeps it honest.

.dev/ROADMAP.md

@@ -674,7 +674,7 @@ ClojureWasm/                         (working dir on disk)
 │   ├── compat_tiers.yaml           per-namespace tier (created at Phase 10)
 │   ├── handover.md                 session-state memo (created when needed mid-task)
 │   ├── debt.yaml                   row-level debt ledger (ADR-0072; replaced the planned known_issues.md)
-│   ├── placement.yaml              Clojure-ns var placement SSOT (ADR-0033; covers the planned status/vars.yaml)
+│   ├── placement.yaml              GENERATED per-var placement index (ADR-0178; supersedes status/vars.yaml)
 │   ├── principle.md                Bad Smell catalogue + revision depths
 │   └── project_facts.md            user-declared invariants (F-001…)
 │
@@ -2048,9 +2048,14 @@ landed); do not create `compat_tiers.md`.
 
 #### `.dev/status/vars.yaml` — SUPERSEDED (not created)
 
-Per-var tracking is covered by `placement.yaml` (Clojure-ns var placement SSOT,
-ADR-0033) + `compat_tiers.yaml` (var/class tier). The originally-planned
-`status/vars.yaml` + `generate_vars_yaml.clj` generator were not built.
+Per-var tracking is covered by `placement.yaml` + `compat_tiers.yaml` (var/class
+tier). The originally-planned `status/vars.yaml` + `generate_vars_yaml.clj`
+generator were not built — and per **ADR-0178** they no longer need to be:
+`placement.yaml` IS a generator's output now (`scripts/gen_placement.sh` reading
+`(cljw.internal/__dump-placement)`), covering every var in every bundled
+namespace, with the `placement_drift` gate failing on any disagreement with the
+code. The hand-maintained form it replaced covered 49 of ~683 `clojure.core`
+publics and had drifted to contradict its own source tree.
 
 ### 15.2 Local reference clones (already present)
 

.dev/cw_v0_parity_and_gap_plan.md

@@ -140,7 +140,7 @@ owning phase decides the concrete design (F-003).
 | G8  | Wasm Component output (`cljw component build`)                       | **Yes (differentiation core)** | F-001/zwasm v2 integration per F-008 spec; **F-010 orders it AFTER the quality loop** (Phase 16). Not v0 (v0 had none); the design is the zwasm-v2 consumer shape                                                                                                                                                                          | **Phase 16** (post-M, zwasm-v2 ready)  | §9.18 Phase 16 (already placeholder)                                                       | D-036/037/038     |
 | G9  | clojure.core remaining (lazy (b) + breadth)                          | **Yes (recurring)**            | Cluster-by-cluster over existing primitives; lazy forms with the lazy-seq Layer-2 wiring                                                                                                                                                                                                                                                   | Recurring quality-loop                 | §9.16 row 14.13 follow-ups + quality-loop rows                                             | D-134             |
 | G10 | multimethods breadth / `&form`/`&env`                                | **Yes**                        | `&form`/`&env` injection into the user-macro path (decide Value shapes for Form/Scope); multimethod breadth audit                                                                                                                                                                                                                          | Opportunistic / test-corpus-driven     | Follow-up rows                                                                              | D-111             |
-| G11 | `--list-vars` / tier introspection                                   | **Yes**                        | `cljw --list-vars` reading `compat_tiers.yaml` + `placement.yaml` (SSOTs ready); shared completion source for G1 nREPL + G2 REPL                                                                                                                                                                                                           | Quality loop                           | New §9 row                                                                                 | file new D-NNN    |
+| G11 | `--list-vars` / tier introspection                                   | **Yes**                        | `cljw --list-vars` over `compat_tiers.yaml` + `placement.yaml`; shared completion source for G1 nREPL + G2 REPL. NOTE 2026-08-04: `--list-vars` is still unbuilt, but its data source now exists for real — ADR-0178 made `placement.yaml` a generated, total, gated index derived from `(cljw.internal/__dump-placement)`, so the CLI is a formatting job over `src/runtime/introspect.zig` rather than a yaml-plumbing one                                                                                                                                                                                                           | Quality loop                           | New §9 row                                                                                 | file new D-NNN    |
 | G12 | generational GC                                                      | **Defer**                      | Both sides future (ROADMAP §89.2); cw v0 reached maturity without it. Not a near-term gap                                                                                                                                                                                                                                                 | Far future                             | §89.2 reserve                                                                              | (none)            |
 
 ### Cross-cutting ordering note

.dev/decisions/0033_clojure_ns_placement_naming_polymorphism.md

@@ -381,3 +381,21 @@ Phase 6.16.a-0 cycle 以降の Affected files:
   (public wrapper / user qualified denied / filter denied / same-ns
   ok)。 D-071 row 更新は次 commit (sub-cycle b/c/d で ADR-0035 完了
   時に併せて Part 3 完了に flip)。
+
+- **2026-08-04 (ADR-0178)**: the **migration schedule** this ADR carried is
+  recorded **complete**; the **placement rule (D2-D5) is unchanged and still
+  governs new vars**. D-062, the cluster row tracking the Pattern A/B migration
+  of the Phase 6.9-6.11 Zig-written vars, was discharged 2026-05-27 with
+  `clojure.string/escape` as the sole residual (D-094) — but `data/placement.yaml`
+  never followed: 42 of its 49 rows still read `status: transient_zig` for vars
+  whose `.clj` bodies had already shipped, and the file had drifted further
+  (two `leaf_loc` paths pointing at nonexistent files, two of three cited helper
+  scripts never written, no gate reading it, 49 of ~683 publics covered).
+  ADR-0178 replaces the hand-maintained file with a **generated** index derived
+  from `(cljw.internal/__dump-placement)` over every bundled namespace, plus a
+  `placement_drift` gate. What the generated index deliberately does NOT record
+  is D7's aspirational half — "this var's current placement is not its intended
+  one" is a judgement with a barrier and belongs in `.dev/debt.yaml` (today one
+  row, D-094). No forward policy about where future `clojure.core` vars should
+  live is stamped: that would be F-003 seizure over an unbuilt residual, and D5
+  already answers it for hot paths (fast-path = Tag switch).