NIFI-15931: Fetching parameter values in the Connector canvas.

[mcgilman]

Summary

JIRA: NIFI-15931

Surfaces parameter values inline in the Connector canvas so property tables and the codemirror parameter tip can resolve #{param} references without leaving the canvas. Read-only by design: values render in tooltips, but the "Go to Parameter" affordance is hidden because connector-managed parameter contexts are not navigable.

Description

Backend

• New REST endpoint GET /connectors/{connectorId}/flow/process-groups/{processGroupId}/parameter-context on ConnectorResource. Requires READ on the connector, returns a ParameterContextEntity for the PG's bound context, or 204 No Content when no context is bound. Sensitive values are masked via the existing DtoFactory path.
• NiFiServiceFacade#getConnectorParameterContext and its StandardNiFiServiceFacade implementation look up the ConnectorNode, locate the target ProcessGroup, and return its bound ParameterContext.
• DtoFactory#createParameterDto now walks the in-memory inheritance graph of the supplied ParameterContext to populate containingParameterContext (with cycle protection), falling back to the supplied ParameterContextLookup only when no in-memory match is found. This is required because connector-managed parameter contexts are not registered in the global ParameterContextDAO, so the previous lookup-only path returned "Unable to find Parameter Context …" for any inherited parameter on a connector PG.

Frontend

• ConnectorService.getConnectorParameterContext(connectorId, processGroupId) wraps the new endpoint, mapping 204 to null so the caller can distinguish "no context" from a load failure.
• New NgRx action set (loadConnectorParameterContext / Success / Failure) and parameterContext slice on ConnectorCanvasState. Selectors expose the current value to dialogs.
• A single effect, loadConnectorParameterContextOnLoadSuccess$, listens to both loadConnectorFlowSuccess and loadConnectorControllerServicesSuccess, normalizes their payloads, filters out null processGroupIds, and dedupes via distinctUntilChanged on (connectorId, processGroupId). This covers the deep-link case where the user lands directly on /connectors/:id/canvas/:pgId/controller-services (the CS route is a sibling of the canvas route, not a child, so it does not activate the canvas component) without firing duplicate fetches when polling or the canvas → CS transition refires within the same PG.
• The action carries an errorContext: ErrorContextKey chosen by the trigger (CONNECTOR_CANVAS for canvas, CONTROLLER_SERVICES for CS-listing) so loadConnectorParameterContext$ can surface failures on the page the user is actually looking at via addBannerError.
• A shared helper bindConnectorParameterContext(store, teardown$, apply) wires the current parameter context onto the read-only EditProcessor and EditControllerService dialogs for the lifetime of dialogRef.afterClosed(). goToParameter is intentionally left undefined; the property table now hides the "Go to Parameter" menu item whenever the callback is missing (property-table.component.ts).
• @Input() goToParameter?: (parameter: string) => void is now optional on EditProcessor and EditControllerService to match.
• The property-value-tip template and the codemirror parameter-tip template render explicit empty-state copy ("No value set" / "Empty string set") so users can tell unset parameters from values that simply weren't fetched. Both null and undefined are handled because the wire format prunes nulls.
• Canvas reducer also resets cached component data + parameter context whenever connectorId (in addition to processGroupId) changes, so navigating between connectors doesn't briefly leak stale shapes.

Test fixture

• pages/connectors/testing/parameter-context-fixture.ts centralizes the as unknown as ParameterContextEntity cast for test fixtures.

Tests

• DtoFactoryTest: 7 new cases covering null/matching IDs, direct and transitive inheritance, fallback to lookup, cyclic inheritance graphs, and sensitive value masking.
• StandardNiFiServiceFacadeTest: happy path returning the entity, null when no context is bound, and ResourceNotFoundException when the PG cannot be located.
• TestConnectorResource: 200 / 204 / AccessDeniedException cases for the new endpoint.
• Frontend (Vitest): ConnectorService (200 vs 204), connectorCanvasReducer parameter context handling and connector-id reset behavior, ConnectorCanvasEffects (load on canvas + CS deep link, polling/transition dedupe, failure routing per trigger), ConnectorControllerServicesEffects parameter-context binding in the read-only dialog, and property-table canGoToParameter with/without callback. Tooltip rendering for null/undefined/''/non-empty across both property-value-tip and parameter-tip.