Add inline chart editing to the V2 interface

[Paul Lizer (paullizer)]

What this adds

Inline editing for simplechart blocks in the V2 chat, completing the set alongside diagram and image editing.

A generated chart used to be final. If the model picked a pie where a bar was wanted, put a scale on the axis that flattened the story, left the axes unnamed, or got one number wrong, the only remedy was to ask again — which left a second near-duplicate chart below the first with nothing to say which one was current.

Every chart now has an Edit button opening a modal with a live preview and six tabs:

Tab	What's in it
Data	A grid of the chart's labels and series — edit any value, rename/add/remove series, add/remove rows. Scatter and bubble charts get their x/y/size pairs instead.
Design	Chart type, title/subtitle/caption, legend and position, bar width, horizontal, stacked, line smoothing/fill/thickness/point size, doughnut hole, gridlines, data-table toggle
Axes	Axis names, explicit min/max, start-at-zero, linear or logarithmic, category label angle and thinning
Source	The raw payload, validated as it is typed, with a "Lay it out" button
Ask AI	A scoped instruction, same as diagrams
History	Every version, with restore

How it works

The block revision framework was already written kind-agnostic, so storage, addressing, conflict handling, export resolution and the shared-conversation path needed no changes — simplechart was simply admitted as an editable kind.

Every control is a pure source-to-source transform of the chart's own payload. That is what makes a control change a revision like any other: undoable, present in the history, honoured by the server-side export, and visible to a reader in the classic interface. A parallel "chart settings" store would have had none of those properties.

Two rules protect a payload while it is rewritten: a transform mutates the raw parsed JSON rather than the normalised ChartSpec (so fields this client does not read survive), and the serialised form follows the source it came from (so a compact payload is not inflated towards the size cap).

Unlike the diagram editor, the whole panel edits a draft and saves once. The diagram editor saves on each layout click, which is right for two buttons; a chart has dozens of controls, and one revision per click would file twenty documents and make the history unreadable. The saved revision carries an auto-written note naming what changed — "Bar width, Value axis" rather than "Edited".

Payload additions

All optional, all defaulting to what charts already did: yMin, yMax, yScale, xTickRotation, xTickLimit, barWidth, lineWidth, pointRadius, showGridX, showGridY.

Existing charts render byte-identically — verified by diffing PNG hashes from the matplotlib export against the previously committed renderer across every chart kind.

Bugs fixed along the way

• smooth, fill and showDataTable did nothing. All three were parsed by every renderer and applied by none. A chart asking for straight line segments was drawn curved; one asking to keep its numbers private still offered them. Controls were added for them, so they are now wired up in all three renderers.
• Horizontal bar charts scaled the wrong axis. A bar chart on its side draws its values along the bottom, but start-at-zero was applied to the axis carrying the category names — so the setting did nothing on exactly the charts where a truncated scale misleads most.
• matplotlib silently re-enables a grid when line properties are passed with False, which would have made "hide the gridlines" do nothing in exports.
• Code review caught three more in this PR's own new code: set_xlim(bottom=) raising a TypeError into a swallowed guard; a NaN in an AI reply storing a chart no browser can parse; and — worst — no text field could accept a space, because trimmed-on-parse values made React revert the keystroke.

Refactors

The classic client's revision resolution is extracted to chat-block-revisions.js and shared with the diagram renderer, rather than copied. The rule is subtle enough — find by position, confirm by fingerprint, fall back to an unambiguous fingerprint match, otherwise leave the original alone — that two copies would eventually disagree.

Chart drawing is extracted to ChartCanvas.tsx so the editor's preview and the chart in the reply cannot diverge.

Testing

• functional_tests/test_v2_chart_editor.py — 23 checks, including real matplotlib renders proving the new options reach the export, that a value range moves the axis on a horizontal bar chart, and that a hostile payload cannot take the export down
• functional_tests/test_v2_chart_editor_logic.ts — 76 behavioural checks on the transforms
• Existing suites re-run green: test_v2_diagram_editor.py (18), test_message_block_revisions.py (18), test_v2_rich_rendering.py (13), test_v2_visual_style_controls.py (16), test_docs_app_surface_coverage.py, test_docs_site_quality.py, test_conversation_export_mermaid_tex_images.py, test_v2_collaboration_visual_style_fix.py
• npm run build and tsc --noEmit clean

No new settings, no new admin surface, no new npm or CDN dependency — Chart.js is already vendored and loaded on demand.

Version 0.261.060 → 0.261.061 (developed as 0.261.059, renumbered on merging the updated base). Documented in V2 Inline Chart Editing.