[jonaraphael]

CSV files need a table comparison that identifies changed cells and keeps inserted/deleted records aligned. Add CSV: Compare Files as Table, available from an active file plus a picker or two selected Explorer files. One read-only webview displays both inputs, highlights original/modified cell differences, synchronizes both scroll axes and multiline row heights, and provides page/change navigation. Long filenames stay on one line with their full escaped names in tooltips.

Related to #67 and #86. This provides an explicit comparison for a known URI pair; it does not replace native Git/PR custom-editor diffs or fully resolve those native integration requests.

Behavior and limits

• Read current VS Code TextDocuments, including dirty edits and VS Code's selected decoding. Source changes refresh the comparison. Both panes are read-only; no file writes, cell-value logging, uploads, or persistent table data are added.
• Align equal records with bounded LCS/unique-row anchors, then use shared-field similarity to pair nearby replacements. Missing records/fields have placeholders; field presence and decoded cell values are compared, not source quoting or line-ending style. The first record remains data.
• Honor csv.enabled, separator overrides/settings, and csv.maxFileSizeMB. Independently reject saved sources above 10 MiB before opening TextDocuments, even when the configured soft limit is zero; stat-less sources must already be open. Decoded input is capped at 5 MiB, 10,000 records, 100,000 cells, 1,000 columns, 64 Ki characters/value and 256 Ki characters/record. Pages cap rendered body rows/cells/text; a visible notice identifies large sections that fall back to positional alignment after the work budget. No data is silently truncated.
• Add one command/context-menu entry and README documentation; no new settings.

Native API limitation

The supported stable CustomTextEditorProvider API supplies one document/webview at a time. The installed VS Code 1.117.0 native-source probe and VS Code 1.100 tab DTO implementation do not expose a reliable TabInputTextDiff pair when the native comparison contains custom editor inputs. VS Code's shared custom diff editor work is outside this extension's stable API contract. The native reopen-as-text implementation replaces the active custom input with one canonical resource, so this PR does not add a fallback that could discard the pair. These are source/API findings, not an end-to-end native Git diff test.

Validation

• Node 20: npm ci, npm run compile, npm test — 190/190 passing, including 22 new behavior tests.
• npm run lint — zero errors; the existing 87 curly warnings remain.
• npm run package -- --out /tmp/csv-table-compare.vsix — passed, including the new external script and compiled modules.
• Model regressions cover insert/delete plus modification, duplicate rows, multiline/doubled quotes, CSV/TSV/PSV, BOM/Unicode, ragged empty fields, exact-once source coverage, bounded large alignment/fallback, malformed/oversized input and page limits.
• Host/frontend regressions cover dirty/reopened document refresh, errors/disposal, huge-source checks before opening with maxFileSizeMB=0, stat-less remote input, picker cancellation, escaped values/titles, read-only controls, filename layout contract, matching row heights, both scroll directions, bounded page replacement, stale/last-change requests restoring controls, and focus positioning with pane/table offsets and a sticky header.
• Independent actual Chromium fixture QA passed: highlights and literal markup escaping, long/short filename pane origins, all 22 paired row heights (including 180px multiline rows), horizontal/vertical synchronization in both directions, and Next Change positioning exactly below the sticky header after a geometry correction. The fixture runs the real model/HTML/script with a mocked host; it is not a native VS Code integration test. Screenshot retained locally at /tmp/csv-table-comparison-review.png.

Stacked on #119 (codex/large-file-preview); this diff adds only the comparison command, implementation and tests.

Independent orchestrator clearance: final head 2ceb421 passes compile, lint and all 190 tests. A dedicated clean npm ci install of the combined checkout passes compile, lint (0 errors; 86 existing warnings) and 286 tests. Current GitHub CI succeeds and the PR is mergeable. Independently verified actual browser geometry: long/short filenames have equal pane origins; all paired row heights match; scrolling synchronizes in both directions and axes; change navigation clears the sticky header exactly; literal HTML remains text. This clears the explicit comparison feature for review, with the native Git/PR integration limitation above retained.