feat: ephemeral measures UI for explore and canvas dashboards

[nishantmonu51]

Frontend for ephemeral measures (labelled "Adhoc measures" in the UI) on top of the expression measure compute added in #9855: users define ad-hoc measures like profit = revenue - cost in the UI, without editing the metrics view YAML.

• Explore: create and edit ephemeral measures from the measures selector and the pivot sidebar (EphemeralMeasureDialog). Definitions live on the explore state and are honored by every view: big numbers, time series, leaderboards, dimension table, time dimension detail, pivot (including comparison chips, conditional formatting and exports).
• URL state and presets: definitions are encoded in the ephemeral URL param (name, display name, expression, optional format preset) and in ExplorePreset.ephemeral_measures, so shared links, bookmarks and the most-recent-state loader reproduce them. Invalid or unknown definitions are dropped with a user-visible error, along with any columns or sorts that reference them.
• Canvas: components with measure fields (KPI, KPI grid, table/pivot, leaderboard, all charts) accept a calculated_measures renderer prop, editable from the inspector (EphemeralMeasureEditor) and offered inline from the field selectors. Requests attach the expression compute and labels/formatters resolve like for any spec measure.
• Validation: a client-side parser (expression-parser.ts) mirrors the runtime allowlist (arithmetic, numeric literals, parentheses, unary minus, abs/round/floor/ceil/sqrt/ln/exp/power/coalesce/nullif/greatest/least) and gives inline errors. Names must not collide with metrics view fields or comparison accessor suffixes, and expressions can only reference plain measures (no window, required-dimension or time-comparison measures).
• Sharing surfaces: public URLs keep only ephemeral measures whose referenced measures are visible to the recipient; alerts and scheduled reports never prefill an ephemeral measure since the saved query has no definition to resolve it against.
• Adds EphemeralMeasure to the DashboardState proto for the legacy proto-state path.

Part of PLAT-135

Checklist:

• Covered by tests
• Ran it and it works as intended
• Reviewed the diff before requesting a review
• Checked for unhandled edge cases
• Linked the issues it closes
• Checked if the docs need to be updated. If so, create a separate Linear DOCS issue
• Intend to cherry-pick into the release branch
• I'm proud of this work!

[AdityaHegde]

Measure used for QA issues in openrtb project,

name: spending_per_million_impressions
expr: overall_spend/ impressions * 1000

1. Getting effect_update_depth_exceeded when sorting by computed measure in dimension display. Not a 100% sure what is triggering this, doesnt always happen.
2. Seeing invalid measure \"spending_per_million_impressions\": measure \"spending_per_million_impressions\" not found for this measure's time series query error when comparing by dimension.
3. Report dialog's Columns section doesnt show displayName, shows the raw name instead.
4. Computed measure is not carried over to Open in browser in report email. It is present in the csv download.
5. Alert seems to not recognise an ephemeral measure.

UX feedback,

1. Do we need the measure in url even if it hidden? When user has a lot of such measures the url can unnecessarily get bloated. How about saving these in localStorage by metrics view? Any place this metrics view is referenced, user can add ephemeral measures to visible measure, including canvas. One big advantage is the measures are not lost if the user has not saved a bookmark.
2. Should we show a warning when creating public url? If a dependant measure is hidden the computed measure gets hidden and the user wont know exactly why.
3. Context columns like delta are not displayed for these measures. Feels a bit weird when timeseries has a line for comparison time range but no context column. I am guessing this is because we have oneof for MeasureCompute? Is it planned to support both?
4. Do we need nulls last when sorting these? Or is it intended to show null at the top when sorting in desc order?
5. In pivot you can add a measure from sidebar but only edit it if it is added to columns. Maybe we should add an edit in sidebar as well?

[AdityaHegde]

Probably out of scope of this PR, but there seems to be a lot of duplication here if we need to add 5 instances for ephemeral editing.

Subcomponent is one option for shown vs hidden items. For tooltip maybe we can add a MaybeShowTooltip helper component.

[nishantmonu51]

Extracted DashboardMetricsItemLabel, which owns the label, the ƒx marker and the edit button. The five call sites are now one component each and the file drops 51 lines.

[AdityaHegde]

This also feels like a generic component like MultiFieldInput is responsible for a measure editor.

[nishantmonu51]

The editor is mounted once at the inspector root (ComponentsEditor) and driven by canvasEphemeralMeasureEditor. The field inputs only set that store, so they no longer own an editor.

[AdityaHegde]

How about reusing the filters parser? We use nearly and not hand write tokeniser and grammer. We could maintain the allow list only to match measure_expression.

Another option is to add an API to compile and get errors from backend.

[nishantmonu51]

Replaced the hand-written tokeniser and recursive-descent parser with a nearley grammar (measure-expression.ne), built by build-measure-expression-grammar alongside the filter and rill-time grammars. The allow-list check against the metrics view stays in the parser wrapper.

[nishantmonu51]

On the reported bugs:

2. measure not found when comparing by dimension — fixed in c62e986. Comparing by dimension flips the TDD chart to a Vega stacked bar (chart-series.ts:95), which builds its own query through the component chart provider. createTDDCartesianSpec never set adhoc_measures, so the measure went out as a bare name and hit the no-compute branch of ResolveMeasure. Definitions now thread MeasureChart → TDDChart → createTDDCartesianSpec. That is also why it looked intermittent: it only affects the Vega chart types, which is exactly what comparison-by-dimension switches into.

3. Report dialog columns now resolve ephemeral measures to their display name, and they can be re-added as columns.

4. Open in browser recovers the definitions from the report's saved query, so it no longer depends on the stored dashboard state.

5. Alerts accept ephemeral measures now — the saved query embeds the expression, so the name resolves without dashboard state. Comparison and percent-of-total criteria stay disabled for them, since LookupMeasure resolves those computes against the metrics view.

1. effect_update_depth_exceeded — reproduced and fixed in d4cfd07. See the follow-up comment below; this paragraph originally said it was not reproduced.

UX points 1-5 are unaddressed and still open for discussion.

[nishantmonu51]

1. effect_update_depth_exceeded — reproduced in the browser and fixed in d4cfd07.

timeoutID in DimensionTable.svelte was $state, and the effect that suppresses cell tooltips while scrolling both reads it (to clear the pending timeout) and writes it. Each write re-ran the effect, which wrote again, until Svelte aborted. Nothing renders timeoutID, so it is now a plain variable.

Sorting by an ephemeral measure is what surfaced it: the measure has no context columns, so switching the sort to it resizes the table, which fires the scroll handler that sets scrolling. That is also why it looked intermittent — the loop needs a scroll event, not the sort itself. Verified against the local dev project: before the change the first click on the column header threw; after it, sorting plus vertical and horizontal scrolling produce no errors.

Worth noting the loop was never specific to ephemeral measures — any scroll of the dimension table could hit it.

[nishantmonu51]

On the UX feedback, addressed in f7576ee:

1. Definitions now live in a per-metrics-view localStorage library (rill:app:adhoc-measures:<metricsView>), so they survive without a bookmark and are shared by every explore on that metrics view. The URL carries only the definitions the explore state references, so hidden ones no longer bloat it. Canvas still keeps definitions on the component; consuming the shared library there is a follow-up.

2. Creating a public URL now lists the ad-hoc measures that will be dropped, with the hidden measures each one references.

3. Supported now, not a oneof limitation. ResolveMeasure resolved comparison and percent-of-total base measures via LookupMeasure, which only sees metrics view measures; resolveReferencedMeasure also resolves expression measures defined in the same query. Delta, delta percent and percent of total all work for ad-hoc measures, and the frontend gates are gone.

4. Not intended. Both dialects now emit NULLS LAST regardless of direction, and safe divide returns NULL via NULLIF(den, 0) instead of infinity or NaN.

5. Added edit and delete to the pivot sidebar.