@@ -4,9 +4,9 @@ This directory holds research notes about the Vortex type system. The notes are
 at `5fc5cb8` (2026-10-17). They live on the `ct/ext-types-research` branch and are not meant to be
 merged.
 
-Reviews on 2026-10-22 and 2026-10-23 updated the Decimal notes and [`decisions.md`](decisions.md).
-Part 4 of the Decimal notes holds the implementation plan for `Narrow` and the canonical decimal
-fix.
+Reviews on 2026-10-22, 2026-10-23 and 2026-10-26 updated the Decimal notes and
+[`decisions.md`](decisions.md). Part 4 of the Decimal notes holds the implementation plan for
+`Narrow` and the canonical decimal fix, and the state of each PR.
 The decimal, DecimalByteParts, serialization and versioning code that the notes cite is the same on
 `develop` at `dbaf5f8` (2026-10-22).
 
 
@@ -34,7 +34,6 @@ gives file and line references for each one.
 | The scalar path and the array path disagree | A decimal scalar casts to `f32` and `f16`. The array cast supports only `f64`, so an array cast to `f32` fails with "No CastKernel". A throwaway test confirmed the `f32` case |
 | `Decimal` duplicates `Primitive` | It has its own canonical variant (51 dispatch sites), builder, compare, arithmetic and aggregates. Decimal-specific files hold about 7,600 non-test lines |
 | DecimalByteParts carries the decimal dtype | It splits wide integers into 64-bit parts, but only decimals can use it |
-| The DecimalByteParts cast rule skips a nullability check | For a cast that changes only the nullability, the rule casts the most significant part. It does not first make sure that the change is safe without execution, as other cast rules do with `Validity::trivially_cast_nullability` |
 | Unknown enum values decode silently | An unknown `values_type` decodes as `I8`. An unknown protobuf `PType` decodes as `U8`, and Variant metadata stores protobuf dtypes in files |
 | Shared code has decimal special cases | Bloom filters, `IN` lists, size statistics, sparse arrays, run-end decoding and the row codec each have a decimal path |
 | No 128-bit integer columns | DuckDB `HUGEINT` cannot be imported, although decimal storage already holds 128-bit values |
 
@@ -340,10 +340,9 @@ width in memory. This applies to existing files and to files that are written in
 maintainer accepts this cost, because the bar of no compute regression applies to the final state
 (decided, D19).
 
-The DBP cast rule has a bug that is independent of these changes. For a cast that changes only the
-nullability, the rule casts the MSP without the check that other cast rules make with
-`Validity::trivially_cast_nullability`. The fix lands as its own PR
-([part 3](03-roadmap.md#independent-changes)).
+The DBP cast rule pushes a nullability cast into the MSP, which holds the validity, and the MSP
+cast fails on a null row. #10798 documents this as a valid form of cast rule, so the rule needs no
+change. FX2 (#10746), which added a `trivially_cast_nullability` guard, closed without a merge.
 
 ## Where structural encodings sit
 
 
@@ -131,12 +131,11 @@ into PRs, with one brief for each PR.
    decimal part must also land before the read plugin converts old nodes, because the detection
    of old nodes reads this field. The same PR fixes eleven `PType` fields of array and layout
    metadata with the same fallback (decided, D34).
-2. **The DecimalByteParts nullability fix.** For a cast that changes only the nullability, the
-   cast rule casts the MSP without the check that `Validity::trivially_cast_nullability` makes in
-   other cast rules. The fix adds that check, as PR
-   [#10230](https://github.com/vortex-data/vortex/pull/10230) did. It also adds a cast kernel for
-   the case that needs execution, so that a declined cast still runs on the parts. It lands as its
-   own PR with tests, and it needs no issue.
+2. **The DecimalByteParts nullability guard (dropped).** This step added the
+   `Validity::trivially_cast_nullability` guard of PR
+   [#10230](https://github.com/vortex-data/vortex/pull/10230) and a cast kernel to the cast rule.
+   It closed without a merge as #10746. The rule pushes the cast into the MSP, and the MSP cast
+   fails on a null row, so no result was wrong. #10798 documents that form as valid.
 3. **Extension opacity fixes (N1).** These are the urgent changes in
    [part 4 of the extension notes](../extension-types/04-urgent-changes.md).
 4. **The integer `Narrow` in memory.** The draft PRs
 
@@ -22,6 +22,11 @@ planning review on 2026-10-23.
   (`/Users/connor/spiral/vortex-data/vortex1/research/`), or tell it to read the files with
   `git show ct/ext-types-research:research/<path>`. Do not change a brief while an agent works from
   it. If a brief must change, tell that agent.
+- When a PR opens, merges or changes scope, the agent updates its line in the collapsed PR list of
+  [#10701](https://github.com/vortex-data/vortex/issues/10701) or
+  [#10733](https://github.com/vortex-data/vortex/issues/10733) with `gh issue edit`. It edits only
+  that line, and it reads the issue again just before it writes, so that it keeps the edits of
+  others. It does not edit this branch to record progress.
 - The briefs cite `develop` at `b70206818f`. Line numbers move as PRs land, so the agent reads the
   cited code before it changes it. Code from the local integer `Narrow` rewrite is cited with its
   commit, for example `f7408481ce:vortex-array/src/arrays/narrow/mod.rs`. That rewrite is a
@@ -57,7 +62,7 @@ planning review on 2026-10-23.
 | ID | PR | Hard dependencies | Size |
 | --- | --- | --- | --- |
 | FX1 | Strict decoding of stored `DecimalType` and `PType` values, in three commits | None | Medium |
-| FX2 | DecimalByteParts nullability cast follows the cast-rule contract | None | Small |
+| FX2 | Dropped. #10798 documents the cast-rule contract instead (see the FX2 brief) | None | None |
 | FX3 | Dictionary `fill_null` no longer truncates the fill code | None | Small |
 | NR1 | In-memory integer `Narrow`, with `encode`, the deprecated `encode_values`, the serialization workaround and a flatten rule | None | Large |
 | NR2 | Benchmarks for compute on integer `Narrow` | NR1 | Medium |
@@ -83,18 +88,12 @@ Later work: LT1 puts both formats into `core` and decides the end of the seriali
 workaround. LT2 is the max pass in DecimalByteParts decoding (D16). LT3 is the pushdown of sum,
 min and max into the MSP (D19). LT2 and LT3 wait until benchmarks show that they are needed.
 
-## Status
+## Progress
 
-The first wave opened on 2026-10-23 as draft PRs, all based on `develop` at `3974ee069c`:
-
-| ID | PR | Note |
-| --- | --- | --- |
-| FX1 | #10755 | Three commits, as planned. Its tests use a new `test_harness::assert_serde_error` helper |
-| FX2 | #10746 | As planned |
-| FX3 | #10745 | Fixes #10623. Non-nullable codes keep the fast path, because they need no fill code |
-| CD1 | #10752 | The compress bench enables the default `core` edition, so the decimal scheme uses its v1 variant |
-| CD2 | #10753 | Adds `fixtures_build_canonical_decimal_widths`, and two columns at precisions 1 and 3 |
-| None | #10747 | The versioning docs describe the scheme variants that #10076 added |
+The collapsed PR lists in [#10701](https://github.com/vortex-data/vortex/issues/10701) and
+[#10733](https://github.com/vortex-data/vortex/issues/10733) track the state of each PR: its link,
+whether it merged, and short notes. Agents update those lists. This branch changes only when a
+brief or a decision changes.
 
 ## Graph
 
@@ -106,7 +105,6 @@ dependencies: the release gate of the compat fixtures (D31), and NR6 merging aft
 flowchart TD
     subgraph FIX["Independent fixes"]
         FX1["FX1 Strict decoding"]
-        FX2["FX2 DBP nullability cast"]
         FX3["FX3 Dict fill code"]
     end
     subgraph NR["Integer Narrow"]
@@ -170,8 +168,6 @@ flowchart TD
     NR5 --> WR3
 ```
 
-FX2 has no edge. It can land at any time.
-
 ## Order of work
 
 A PR can start when its dependencies have merged. The waves group the PRs whose dependencies merge
@@ -180,7 +176,7 @@ files. The column "Shared files" names the pairs that do not, so run those one a
 
 | Wave | PRs | Note | Shared files |
 | --- | --- | --- | --- |
-| 1 | FX1, FX2, FX3, NR1, CD1, CD2, CD3 | No dependencies. The next regular release after CD2 publishes the fixtures | CD2 calls `smallest_decimal_value_type`, which CD3 removes. The second of the two to merge adapts |
+| 1 | FX1, FX3, NR1, CD1, CD2, CD3 | No dependencies. The next regular release after CD2 publishes the fixtures | CD2 calls `smallest_decimal_value_type`, which CD3 removes. The second of the two to merge adapts |
 | 2 | NR2, NR6, CD7, CD5 | NR6 merges after NR5 (D35). CD7 waits for CD1. CD5 waits for the release with CD2 | CD5 and CD7: the crate doc in `encodings/decimal-byte-parts/src/lib.rs`, the tests in `assemble.rs`, and `benches/dbp_assemble.rs`. CD7 also changes the signature of `split_decimal`. NR6 and CD7: the golden snapshots of `vortex-btrblocks` |
 | 3 | NR3, then NR4 | One stack. Merge NR1 and NR2 before reading the CodSpeed reports of NR3 and NR4 | None |
 | 4 | NR5, CD4 | NR5 waits for FX3 | Both edit `vortex-array/src/arrays/narrow/rules.rs` |
@@ -217,14 +213,14 @@ publishes the CD2 fixtures also gates CD5 and CD6, so CD2 is worth landing in wa
 ## Follow-up issues
 
 These problems came up during planning and the first wave of PRs. They are outside the planned
-PRs, and each one has its own issue.
+PRs, and each one has its own issue. Two are closed.
 
 | Issue | Problem |
 | --- | --- |
 | #10748 | Generic structural encodings always sit above other encodings. NR5 does this for `Narrow` only |
 | #10749 | Decimal `scalar_at` and `min_max` panic on a stored value outside the precision, which a file read can produce |
-| #10750 | Seven cast rules (RunEnd, ZigZag, FoR, RLE, ALP, ALP-RD, DateTimeParts) push nullability casts without the guard that FX2 adds to DecimalByteParts |
-| #10751 | The FoR scheme bit-packs its child outside the allowed schemes, so its child skips the edition filter |
+| #10750 | Closed as not planned. The push-down cast rules return no wrong result, and #10798 documents them as a valid form |
+| #10751 | Closed by #10757. The FoR scheme now declares and refines its bit-packing child |
 | #10754 | The compat harness: no CI job runs `--mode all`, one failing fixture stops the whole check, and the README describes `--git-ref` wrongly |
 | #10756 | Corrupt ALP-RD, RLE and RunEnd metadata can panic a file read |
 
 
@@ -77,12 +77,13 @@ The notes come from reading `develop` at `5fc5cb8`, RFC drafts, issues and pull
 2026-10-19 the review also read the draft `Narrow` PRs and PR #10230. On 2026-10-22 it read the
 versioning spec, the array plugin and serialization code, and the DecimalByteParts code. It also
 read the history of the decimal compression scheme, and PRs #10305 and #10314. On 2026-10-23 it
-traced which statistics the compressors store on the DecimalByteParts parts, read the decimal
-types of arrow-rs 59.3, and read the cast change of PR #10230. A second review on the same day
-read when the reader attaches stored statistics, the DecimalByteParts constructor and compressor
-scheme, the compat harness, and the edition families. A planning review on the same day had five
-agents draft the PR briefs from the code at `b70206818f`, and the review checked their main claims
-in the code. One throwaway Rust test confirmed
-the `f32` cast disagreement and the `ext_storage` pushdown rules (probes R1 and R6 in the extension
+traced which statistics the compressors store on the DecimalByteParts parts, read the decimal types
+of arrow-rs 59.3, and read the cast change of PR #10230. A second review on the same day read when
+the reader attaches stored statistics, the DecimalByteParts constructor and compressor scheme, the
+compat harness, and the edition families. A planning review on the same day had five agents draft
+the PR briefs from the code at `b70206818f`, and the review checked their main claims in the code.
+On 2026-10-26 it read the state of the first PRs, and PRs #10798 (the cast-rule contract), #10757
+(the FoR scheme) and #10080 (error types without categories). One throwaway Rust test confirmed the
+`f32` cast disagreement and the `ext_storage` pushdown rules (probes R1 and R6 in the extension
 notes). One short Python script checked byte order. Section 10 of the report lists the claims that
 are not verified, which include every performance claim.