Row, column and freeze commands act on the sheet they are given (sheet, or a Sheet! prefix)

[CouchRiv]

view.freezePanes, home.rowHeight, home.columnWidth and the other row and column commands always changed the active sheet. A sheet parameter was accepted and silently ignored, so a programmatic caller (MCP, control channel, CLI) laying out a sheet that isn't active got a success while the frozen panes, widths or heights landed on the active sheet, over what it had set there before. Found while building a four-sheet review workbook through MCP: the panes and column widths meant for two other sheets ended up on the first one.

Repro on main (fc45b7f), gridcraft-cli mcp, after home.insertSheet {name: "Data"} and sheet.activate {sheet: "Sheet1"}:

call	main	this branch
view.freezePanes {sheet: "Data", cell: "A2"}	{"freeze":[1,0]}, applied to Sheet1	applied to Data
home.columnWidth {sheet: "Data", cols: "A:A", chars: 30}	Sheet1!A:A resized	Data!A:A resized
home.rowHeight {sheet: "Data", rows: "1:1", height: 40}	Sheet1 row 1	Data row 1
home.columnWidth {cols: "Data!B:B", chars: 30}	invalid parameters for cols: not a range: Data!B:B	Data!B:B resized
view.freezePanes {cell: "Data!A2"}	Data!A2 for cell names a sheet other than the one this command works on	Data frozen at A2

Saved file on main: sheet1.xml has the <col> and <row ht>, sheet2.xml (Data) has no pane, no <cols>, no row height. On the branch it's the other way round.

What changed

• format.rs: line_targets now returns the sheet with the lines. The sheet is sheet (name or index, through target_sheet like home.insertRows or data.validation), else a Sheet! prefix on rows/cols ("Data!B:B,D:F", same convention as range in target_ranges), else the active sheet. A prefix that contradicts sheet is an error; a null sheet counts as absent, as in target_sheet (second commit). home.rowHeight, home.columnWidth, home.autofitRowHeight, home.autofitColumnWidth, home.hideRows/hideColumns/unhideRows/unhideColumns use it; home.defaultWidth uses target_sheet.
• view.rs: view.freezePanes resolves its sheet the same way, so sheet works and a cell prefixed with another sheet freezes that sheet instead of being refused. view.freezeTopRow, view.freezeFirstColumn and view.unfreezePanes take sheet.
• The selection belongs to the active sheet, so on another sheet these commands need explicit rows/cols (or cell for Freeze Panes) and say so (missing cols: the selection is on the active sheet) rather than reusing the active sheet's selection.
• Without sheet or a prefix nothing changes, so the UI (header drags, dialogs, context menus) behaves as before.
• The params texts list sheet? and the prefixed form. The Freeze Panes one also says that without cell it unfreezes a frozen sheet, since a misspelt cell key otherwise removes the panes without a word.

Verification (Linux x86_64)

• cargo test -p gridcraft-engine --lib tests::line_sizes_and_freeze_panes_take_a_sheet: with Sheet1 active, freezes, sizes, hides and sets the default width on Data through sheet (by name and by index) and through prefixes, checks Data and that Sheet1 is unchanged, then a null sheet with a prefix and the error cases. On main it fails at home.columnWidth {cols: "Data!B:B,D:D"} (not a range); with that line removed it fails at the first check, data.freeze left: None, right: Some((1, 0)). Passes here.
• gridcraft-mcp: tests::other_sheet_prefix_is_error no longer expects Freeze Panes to refuse Other!B2, and keeps the "never silently fall back to the active sheet" check with formulas.tracePrecedents; tests::cross_sheet_cell_refs_resolve now checks that Other!C4 freezes that sheet and leaves the active one alone (read back with inspect_workbook).
• The MCP repro above replayed on a release build of the branch.
• cargo fmt --all -- --check, cargo clippy -p gridcraft-engine -p gridcraft-mcp --all-targets -- -D warnings, cargo test -p gridcraft-engine -p gridcraft-mcp

Limits

• Other commands that act on the active sheet still ignore sheet: the View › Show flags, grouping and outline, page breaks and Page Layout settings (margins, orientation, print area, print titles). Same fix if you'd like it here, or a follow-up. A dispatcher-level answer (reject unknown parameter keys by comparing with the params text, so {"cel": "A2"} fails instead of unfreezing) is a bigger design question I left out.
• Also seen: data.validation with an unknown type ("lst") succeeded and saved type="none"; fixed separately in Data validation: a list typed without quotes is saved as a quoted list, and an unknown type is refused #1084.
• Format: Row Height and Column Width say pixels, and take points like Excel #1085 (units of home.rowHeight / home.columnWidth) edits the same two params texts, so the second one to land needs a small rebase. git merge-tree against the open PRs touching these files (MCP: confine file access with --automation-read-root and --automation-write-root (#445) #480, MCP: reject invalid format_range borders as invalid params (#560) #603, cell.set / set_cell: accept a number for input (#697) #720, Security: the --control server requires an auth token and closes bad connections (#777) #783, fix(security): restrict cell hyperlink schemes and require a control-channel token #834, XLSX: write this-row structured references as [[#This Row],[Col]] #869, Conditional formatting: reuse Format Cells controls for custom rule styles #870, Hyperlinks: confirm before opening external links, refuse unsafe schemes #880) is clean.