Streaming read of date cells: cached/compact styles

Cluster: streaming

Scenario

A large workbook is read row-by-row with the streaming reader, and its date cells resolve less context than a buffered read would.

Cached / compact style mode. When style resolution runs in a cache or compact mode, with styles interned and looked up by index rather than fully materialized per cell, the streaming reader's date-typing path can fail to resolve a cell's number format at all, degrading date cells to raw serials or crashing, where the buffered read succeeds.

Spec note, not a corpus case here: the core streaming-date defect, a date-formatted numeric cell streaming as a raw serial because styles are not applied when typing, is already locked as a known-open corpus case (streaming-read-applies-date-format). What this note carries is the root cause that case does not exercise: the cached or compact style mode. It needs a workbook exercised under both buffered and cached-style streaming reads, plus a streaming-read harness that surfaces per-cell resolved values under a chosen style mode, which is new adapter surface.

The 1904 date base was the other half of this note and is now built: workbookPr/@date1904 is read once into Workbook.dateEpoch, both readers hand it to the shared cell decoder, and the writer declares it again. The corpus case workbook-date-system-1904 locks it against Excel-authored fixtures in both serialisations. The ordering hazard the open questions raised is answered rather than avoided: the workbook part is read before any sheet, in both readers, because the date system is an input to every cell decode.

Desired behavior

• Streaming date typing does not depend on full style materialization. Resolving a cell's number format, to decide date against number, works whether styles are fully materialized or held in a cache or compact form. A date cell reads as a date in every style mode, and no mode crashes or silently downgrades a date to a raw serial.
• Parity is the invariant. For the same workbook, streaming and buffered reads agree on both the type (date) and the value of every date-formatted cell.

Open questions

• Does the compact or cache style mode intern the number-format code, which is recoverable, or only a resolved style object, which may omit the numFmt needed for date detection? The fix differs accordingly.

Related: streaming-read-applies-date-format (the default-style face of the same defect), streaming-reader-styles-option-and-defaults, streaming-read-styles-before-cells, date-value-timezone-conversion, xlsx-date-detection-control.