mountainash-io · discreteds · Aug 19, 2026 · Aug 19, 2026 · Aug 19, 2026 · Aug 19, 2026
@@ -2,11 +2,11 @@
 
 <!-- DO NOT EDIT — this file is auto-generated by scripts/generate_divergences_catalog.py -->
 
-> Last generated: 2026-08-13 03:40 UTC
+> Last generated: 2026-08-19 05:24 UTC
 
 ## Overview
 
-Total divergences tracked: **125**
+Total divergences tracked: **128**
 
 ## Summary
 
@@ -62,6 +62,7 @@ Total divergences tracked: **125**
 | IB-DT-07 | ibis-sqlite: microsecond() returns seconds instead of microsecond component | ibis-sqlite | upstream_bug | Strict xfail | Investigating |
 | IB-DT-08 | ibis backends: nanosecond() returns 0 — no sub-microsecond precision from Python datetime | ibis-duckdb, ibis-polars, ibis-sqlite | by_design | Strict xfail | By Design |
 | IB-DT-09 | Ibis today() upcasts date to timestamp and now() uses query-time UTC SQL | ibis-duckdb, ibis-polars, ibis-sqlite | by_design | Accepted (documented) | By Design |
+| IB-DT-19 | SQLite backend memtable registration crashes on null date/timestamp values (NaT binding) | ibis-sqlite | upstream_bug | None | Needs Filing |
 | NW-DT-01 | Datetime offset ops require literal integers — column expressions rejected (parameter-width) | narwhals-pandas, narwhals-polars | parameter_width | Enhanced error message | Open |
 | NW-DT-02 | week_of_year not supported on pandas backend | narwhals-pandas | upstream_feature_gap | Strict xfail | Investigating |
 | NW-DT-03 | dt.time() is not supported on any Narwhals dialect — NotImplementedError | narwhals-pandas, narwhals-polars, narwhals-lazy | upstream_feature_gap | Strict xfail | Investigating |
@@ -122,7 +123,8 @@ Total divergences tracked: **125**
 | IB-REL-10 | ibis-sqlite: drop_nans/unpivot/melt raise OperationNotDefinedError | ibis-sqlite | upstream_feature_gap | Strict xfail | Needs Filing |
 | IB-REL-11 | RESOLVED: ibis-duckdb asof join returned nondeterministic row order | ibis-duckdb | mountainash_internal | None | Resolved (internal) |
 | IB-REL-12 | cross_join between two same-named tables from different Ibis connections raises a column-binding error on SQL backends | ibis-duckdb, ibis-sqlite | mountainash_internal | Strict xfail | Investigating |
-| IB-REL-13 | ibis-sqlite: asof join raises UnsupportedOperationError | ibis-sqlite | upstream_feature_gap | Strict xfail | Needs Filing |
+| IB-REL-13 | RESOLVED: ibis-sqlite asof join raised UnsupportedOperationError | ibis-sqlite | upstream_feature_gap | None | Resolved (internal) |
+| IB-REL-15 | ibis-polars rejects non-equality join predicates, blocking the join_asof forward/nearest emulation | ibis-polars | upstream_feature_gap | Enhanced error message | Needs Filing |
 
 ### Aggregate Operations
 
@@ -765,6 +767,19 @@ Total divergences tracked: **125**
 | Workaround | Accepted (documented) |
 | Last Verified | 2026-07-05 |
 
+### IB-DT-19: SQLite backend memtable registration crashes on null date/timestamp values (NaT binding)
+
+| Field | Value |
+|---|---|
+| Project | ibis |
+| Category | Datetime Operations |
+| Root Cause | upstream_bug |
+| Affected Backends | ibis-sqlite |
+| Status | Needs Filing |
+| Workaround | None |
+| Notes | _register_in_memory_table (ibis/backends/sqlite/__init__.py) stages memtables via op.data.to_frame() (a pandas roundtrip). A null date32 or timestamp value becomes pandas NaT, which sqlite3 cannot bind — crashes create_table/insert for any frame containing a null temporal value. Verified empirically 2026-08-18 against ibis 12.0.0 — raw pyarrow.Table sources are incidentally safe for date columns only (PyArrow's Table.to_pandas() defaults date_as_object=True, so a null date32 becomes Python None, not NaT) but not for timestamp columns; polars/pandas DataFrame sources crash for both date and timestamp columns (their own to_pandas() maps Date to datetime64 directly). Discovered downstream in mountainash-data (DEBT-13), not via mountainash's own cross-backend probe suite — mountainash itself does not yet have a CapabilityFact/DivergenceFact exercising this path. |
+| Last Verified | 2026-08-18 |
+
 ### NW-DT-01: Datetime offset ops require literal integers — column expressions rejected (parameter-width)
 
 | Field | Value |
@@ -1264,7 +1279,7 @@ Total divergences tracked: **125**
 | Notes | ibis-sqlite lacks array/pivot relational translations: Relation.drop_nans()/ unpivot()/melt() raise OperationNotDefinedError; ibis-duckdb/ibis-polars and polars/narwhals compute them. Renamed from a colliding DivergenceFact id (was "IB-REL-07", which already named an unrelated entry above — the ArrayValue.sort() descending-parameter gap) when backlog item 87's id-collision detector caught the reuse; the DivergenceFact and this entry now self-reference via upstream_ref (backlog item 87, 2026-08-13). |
 | Last Verified | 2026-08-13 |
 
-### IB-REL-11: RESOLVED — ibis-duckdb asof join returned nondeterministic row order
+### IB-REL-11: RESOLVED: ibis-duckdb asof join returned nondeterministic row order
 
 | Field | Value |
 |---|---|
@@ -1274,7 +1289,7 @@ Total divergences tracked: **125**
 | Affected Backends | ibis-duckdb |
 | Status | Resolved (internal) |
 | Workaround | None |
-| Notes | Originally described as "asof join is unreliable on Ibis SQL backends" covering both ibis-duckdb and ibis-sqlite. Root-caused 2026-08-18 (PR #297 CI investigation, repeated single-test process runs flipped xfail/XPASS ~50/50): Relation.join_asof() on the Ibis backend never applied an explicit ORDER BY, and DuckDB gives no row-order guarantee for ASOF JOIN output absent one — the query planner nondeterministically returned rows in original or shuffled order run-to-run. This was not a value divergence: join values were always correct, only the row order backing the test's positional assertions flapped. Fixed by ordering the Ibis join_asof result by the join key(s) (relsys_ib_ext_ma_util.py) to match polars/narwhals' left-order preservation. The distinct ibis-sqlite raise (no ASOF JOIN translation) was split off to IB-REL-13, which remains open. |
+| Notes | Originally described as "asof join is unreliable on Ibis SQL backends" covering both ibis-duckdb and ibis-sqlite. Root-caused (2026-08-18, PR #297 CI investigation): Relation.join_asof() on the Ibis backend never applied an explicit ORDER BY, and DuckDB gives no row-order guarantee for ASOF JOIN output absent one — the query planner nondeterministically returned rows in original or shuffled order run-to-run, flipping the strict-xfail test between XFAIL and XPASS(strict) independent of any test-suite change. Not a value divergence — the join values were always correct, only positional-assertion row order flapped. Fixed by ordering the Ibis join_asof result by the join key(s) (relsys_ib_ext_ma_util.py) to match polars/narwhals' left-order preservation. The distinct ibis-sqlite raise (SQLite has no ASOF JOIN translation) was split off to IB-REL-13, which remains a genuine open gap. Renamed from a colliding DivergenceFact id (was "IB-REL-08") 2026-08-13; that history stands, this entry is now closed. |
 | Last Verified | 2026-08-18 |
 
 ### IB-REL-12: cross_join between two same-named tables from different Ibis connections raises a column-binding error on SQL backends
@@ -1290,18 +1305,31 @@ Total divergences tracked: **125**
 | Notes | Verified empirically (backlog item 87, 2026-08-13): Relation.cross_join() raises duckdb BinderException / sqlite OperationalError ("no such column") when the two input tables share a table name but originate from separate Ibis connections (exactly the shape produced by the test suite's BackendDataFrameFactory, which names every table "test_table"); ibis-polars and polars/narwhals are unaffected. Root cause not yet isolated to Ibis vs. mountainash's join visitor — likely a missing table-alias disambiguation when two DatabaseTable operations share a name across connections. Renamed from a colliding DivergenceFact id (was "IB-REL-09", whose yaml entry described a different, no-longer-reproducible "suffixes kwarg" TypeError) when backlog item 87's id-collision detector caught the reuse; the DivergenceFact and this entry now self-reference via upstream_ref. |
 | Last Verified | 2026-08-13 |
 
-### IB-REL-13: ibis-sqlite: asof join raises UnsupportedOperationError
+### IB-REL-13: RESOLVED: ibis-sqlite asof join raised UnsupportedOperationError
 
 | Field | Value |
 |---|---|
 | Project | ibis |
 | Category | Relational Operations |
 | Root Cause | upstream_feature_gap |
 | Affected Backends | ibis-sqlite |
+| Status | Resolved (internal) |
+| Workaround | None |
+| Notes | Split from IB-REL-11 (2026-08-18) after the ibis-duckdb portion (a nondeterministic row-order bug, not a value divergence) was fixed in mountainash by ordering the join_asof result deterministically. This entry tracked the remaining genuine upstream gap: Ibis has no ASOF JOIN translation for the SQLite backend. Resolved (2026-08-19, item 108): every strategy on ibis-sqlite now routes through an Ibis-relational-expression emulation (inner candidate join + windowed rank + left-keep join) instead of native asof_join, matching Polars on every value (scripts/probes/ probe_asof_emulation.py). Two narrower row-order/tie-winner divergences from the emulation and the ibis-duckdb native path are tracked separately as IB-REL-16/IB-REL-17. The DivergenceFact was removed from divergences.py in the same change (Task 3); this entry stays as the historical record, per the IB-REL-11 precedent above. |
+| Last Verified | 2026-08-19 |
+
+### IB-REL-15: ibis-polars rejects non-equality join predicates, blocking the join_asof forward/nearest emulation
+
+| Field | Value |
+|---|---|
+| Project | ibis |
+| Category | Relational Operations |
+| Root Cause | upstream_feature_gap |
+| Affected Backends | ibis-polars |
 | Status | Needs Filing |
-| Workaround | Strict xfail |
-| Notes | Split from IB-REL-11 (2026-08-18) after the ibis-duckdb portion (a nondeterministic row-order bug, not a value divergence) was fixed in mountainash by ordering the join_asof result deterministically. This entry tracks the remaining genuine upstream gap: Ibis has no ASOF JOIN translation for the SQLite backend, so Table.asof_join() raises UnsupportedOperationError on ibis-sqlite. Use a polars or narwhals backend for asof joins on that data. |
-| Last Verified | 2026-08-18 |
+| Workaround | Enhanced error message |
+| Notes | item 108: Relation.join_asof(strategy="forward"|"nearest") lowers to an Ibis-relational-expression emulation (inner candidate join on a non-equality directional predicate, e.g. right.on >= left.on). The Ibis Polars backend raises TypeError("Only equality join predicates supported with pandas") for any non-equality join, so the emulation cannot run there (probe- confirmed on ibis 12.0.0/polars 1.43.2). A CapabilityFact (relations/backends/capabilities/ibis.py) gates this permanently via a predicate on the `strategy` param, raising a clear BackendCapabilityError before the raw TypeError would surface. `backward` is unaffected (native asof_join, no candidate join needed). |
+| Last Verified | 2026-08-19 |
 
 ## Aggregate Operations
 

@@ -5,7 +5,7 @@
 
 Scoped deviations — dialect, parameter, option, value-class; function-level coverage and matrices live in [`expression-coverage.md`](expression-coverage.md).
 
-Declarations: 43 · Facts: 1466 · Registered operations: 326 · Implementation records: 978
+Declarations: 43 · Facts: 1467 · Registered operations: 326 · Implementation records: 978
 
 Legend — scoped deviations:
 
@@ -1984,6 +1984,12 @@ Legend — scoped deviations:
 | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
 | * | tolerance | — | — | unsupported | gate | build | tolerance is not None | join_asof(tolerance=...) is not supported by the Narwhals backend | Drop tolerance= or use the Polars backend. | — | 2026-07-05 | — | — |
 
+### `JOIN_ASOF` × ibis (RKEY_MOUNTAINASH_REL)
+
+| Dialect | Param | Option values | Value class | Level | Enforcement | Boundary | Condition | Message | Workaround | Upstream | Since | Native errors | Probe-exempt |
+| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
+| ibis-polars | strategy | — | — | unsupported | gate | build | — | join_asof forward/nearest lowers to a non-equality candidate join; the ibis Polars backend rejects non-equality join predicates (TypeError: Only equality join predicates supported with pandas). | Use ibis-duckdb/ibis-sqlite, or polars/narwhals backends. | IB-REL-15 | 2026-08-18 | — | — |
+
 ### `READ_RESOURCE` × polars (RKEY_MOUNTAINASH_REL)
 
 | Dialect | Param | Option values | Value class | Level | Enforcement | Boundary | Condition | Message | Workaround | Upstream | Since | Native errors | Probe-exempt |