r2il-mask-abi-probe: V3 facet and V4 call as two readings of one buffer (Round 3)

.claude/board/entries/2026-10-06-v3-v4-dual-reading-round3.md

@@ -0,0 +1,54 @@
+# 2026-10-06 — V3 data and V4 IR as two readings of one resident buffer (Round 3)
+
+## MEASURED
+
+`crates/r2il-mask-abi-probe/tests/v3_v4_dual_reading.rs`, 8 tests, 6 disable
+runs red.
+
+There is one owner: a 64-aligned `[u8; 2 × 512]`. The intake step is
+`FunctionBody::write_into_value_slab`. Two shipped readings run over it with
+no translation between them:
+
+- **V3**: `node_rows_from_le_bytes` → `NodeRow::value` →
+  `FacetCascade::ref_from_bytes` per 16-byte slot.
+- **V4**: `ogar_loco::call_in_slab` under a `LaneShape`, plus
+  `ogar_r2il::{r2il_mask, project}`.
+
+`G6D2` (`6 × FacetTier{lo,hi}`) and `LaneShape::Pairs`
+(`6 × (function:value)`) are the same carving. For all 180 calls, tier `k`
+of slot `l` is call `6l+k`, at the same address (pointer identity).
+`Triples`/`Quads` also read the slab in place.
+
+- An owner write is seen at once by the V3 facet, the V4 call and the R2IL
+  mask.
+- Taking every reading leaves the bytes unchanged.
+- The readings allocate 0 heap bytes. The meter can fire: it sees
+  `materialize_indices`.
+- Per-slot `facet_classid` bytes are V3 data. Rewriting all 30 changes no V4
+  call.
+
+## FINDING
+
+- **Reading is shared; loco execution is not.** `Interpreter` runs a
+  `Program { functions: Vec<FunctionBody> }`. The only path from resident
+  bytes is `read_from_value_slab`, which gathers the 360 payload bytes into a
+  second representation. That is a heap-owned copy at a different address.
+  Reading a stored V4 body is zero-copy; executing it through loco today is
+  not.
+- **The selector is not in the bytes.** The same slab under `Pairs` and
+  `Triples` yields different call streams. No shipped function maps a classid
+  to a `LaneShape`; every caller passes it in. `LocoConcept::FunctionBody`
+  (`0x1701`) is one concept for all three shapes.
+- **Semantic-only difference:** V4 recovers `len` from the last non-zero
+  call (`read_from_value_slab`). A V3 `0:0` tier is valid data, but as V4 it
+  is a NOP and padding. An interior all-zero call cannot be represented.
+
+## OPEN
+
+- No mutable reinterpret (`mut_from_bytes`) exists on `FacetCascade`.
+  Mutation goes through the owner's bytes, which matches "bytes are stored,
+  integers are projected".
+- The classid → reading resolver (classid → `LaneShape`, R2IL vs core
+  dialect) is not shipped; plan W1 / `D-R2IL-5` is still "Not started".
+- The documented `ruff_r2il` defect (`VarnodeFacet` classid lo-u16 = space
+  rank, W0) is not re-tested here; ruff is not in this checkout.

.claude/board/entries/README.md

@@ -25,10 +25,11 @@ index row, (3) no duplicate entry id. Checks 1 and 2 are deliberately
 opposite directions; the stranding this convention prevents shows up in
 exactly one of them, never both.
 
-222 entries, 2026-08-06 .. 2026-10-06.
+223 entries, 2026-08-06 .. 2026-10-06.
 
 | date | entry id | finding | file |
 |---|---|---|---|
+| 2026-10-06 | `v3-v4-dual-reading-round3` |  | [2026-10-06-v3-v4-dual-reading-round3.md](2026-10-06-v3-v4-dual-reading-round3.md) |
 | 2026-10-06 | `D-MORTON-0` |  | [2026-10-06-morton8x8-checked-address.md](2026-10-06-morton8x8-checked-address.md) |
 | 2026-10-06 | `dav-resident-reading-round2` |  | [2026-10-06-dav-resident-reading-round2.md](2026-10-06-dav-resident-reading-round2.md) |
 | 2026-10-06 | `dav-carrier-invariance-quack` |  | [2026-10-06-dav-carrier-invariance-quack.md](2026-10-06-dav-carrier-invariance-quack.md) |

crates/r2il-mask-abi-probe/Cargo.toml

@@ -26,3 +26,13 @@ lance-graph-quack = { path = "../lance-graph-quack" }
 # here matches `crates/symbiont`'s existing `../../../OGAR/crates/...` deps.
 ogar-r2il = { path = "../../../OGAR/crates/ogar-r2il" }
 ogar-loco = { path = "../../../OGAR/crates/ogar-loco" }
+# Round 3 (`tests/v3_v4_dual_reading.rs`): the V3 reading — `NodeRow`,
+# `node_rows_from_le_bytes`, `FacetCascade::ref_from_bytes` — over the same
+# bytes the loco/R2IL reading projects.
+lance-graph-contract = { path = "../lance-graph-contract" }
+
+# `ogar-loco` / `ogar-r2il` take `lance-graph-contract` from git `main`. In
+# THIS workspace that is redirected to the local checkout, so the probe sees
+# one contract identity — the local one — rather than two.
+[patch."https://github.com/AdaWorldAPI/lance-graph"]
+lance-graph-contract = { path = "../lance-graph-contract" }