sheet range set-style unmerges fully covered merged ranges despite style-only contract (v1.0.63) #1497

Environment

DWS v1.0.63, commit 4cd5d05 (2026-10-03). Reproduced on 2026-10-13 with a newly created disposable Sheet containing only synthetic text.

Minimal trigger

Create a disposable Sheet and use nodeId and sheetId returned by create-with-data. No existing business Sheet is needed.

dws sheet create-with-data --name DWS-MERGE-REPRO --values '[["","SYNTHETIC_TITLE","","CONTROL"],["","SYNTHETIC_GUIDE","",""],["CONTROL","","",""]]' --format json
dws sheet merge-cells --node NODE_FROM_CREATE --sheet-id SHEET_FROM_CREATE --range B1:C1 --format json
dws sheet info --node NODE_FROM_CREATE --sheet-id SHEET_FROM_CREATE --format json
dws sheet range set-style --node NODE_FROM_CREATE --sheet-id SHEET_FROM_CREATE --range B1:C1 --font-weight bold --format json
dws sheet info --node NODE_FROM_CREATE --sheet-id SHEET_FROM_CREATE --format json
dws sheet range read --node NODE_FROM_CREATE --sheet-id SHEET_FROM_CREATE --range A1:D3 --format json

Before set-style, mergedRanges is ["B1:C1"]. The style call succeeds. Afterward, mergedRanges is [], while the values are unchanged and both cells have fontWeight=bold. One pre-existing merged block and one style-only write suffice.

The dry-run translates the write to set_cell_range with only nodeId, sheetId, rangeAddress, and cells=[[{cellStyles:{fontWeight:"bold"}},{cellStyles:{fontWeight:"bold"}}]]. It contains no value or explicit unmerge operation.

Expected behavior

Pure style writes should preserve existing merged ranges, or explicitly reject unsupported shapes without changing structure. The pinned source documents style-only writes as safe for merged cells:

Isolation matrix

Before each case we restored B1:C1 and B2:C2 and read both structure and A1:D3 content. Each case contained one operation. Standalone and batch-update produced the same merge-preservation and value outcomes. Their error envelopes differ for the full merged-range value case: standalone returns MERGED_CELLS_CONFLICT, while batch-update returns stateServer.invalid_operation with MERGED_CELLS_CONFLICT as the cause. The standalone B1:C1 value case was separately reconfirmed on the same version with raw stdout/stderr, exit code, and complete before/after reads:

A separate style-only B1:C2 write removes both merged blocks. Values remain intact throughout the style probes. All range reads reported hasMore=false. The batch variant used exactly one range set-style operation, ruling out interactions with other subcommands.

Temporary compatibility handling

After reading the original merge ranges and proving subordinate cells contain no unique values, a strict batch containing the style write followed by explicit merge-cells (B1:C2, mergeRows) restored both original merges. A subsequent info/range read verified both merges, all values, and the requested bold style. This is a caller workaround verified only on the disposable synthetic sample; the underlying merged-range preservation issue still needs correction.

Limits

The reproduction identifies the public operation and range shape that changes structure. Server-side implementation is not visible, so this report does not claim whether the final defect lies in CLI translation or the remote Sheet tool. No credentials, personnel records, internal document links, or original business payloads are included.