feat(spec-dashboard): support explicit emitter coverage groups

cspell.yaml

@@ -283,6 +283,7 @@ words:
   - strs
   - stubbed
   - swaggerui
+  - tabular-nums
   - TCGC
   - TEAMPROJECTID
   - terlson

packages/spec-dashboard/README.md

@@ -1,5 +1,37 @@
 # Spector Dashboard
 
+## Coverage overview groups
+
+Use `groupEmitters` to combine emitters into named overview cards:
+
+```tsx
+<Dashboard
+  coverageSummaries={coverageSummaries}
+  showOverview
+  groupEmitters={[
+    {
+      name: "C#",
+      emitters: ["@azure-typespec/http-client-csharp", "@azure-typespec/http-client-csharp-mgmt"],
+    },
+  ]}
+  emitterDisplayNames={{
+    "@azure-typespec/http-client-csharp": "C# (Data plane)",
+    "@azure-typespec/http-client-csharp-mgmt": "C# (Management plane)",
+  }}
+/>
+```
+
+Each card shows the union of its emitters' coverage, with individual percentages underneath.
+A scenario counts once per table and is covered if any member reports `pass`, `not-applicable`,
+or `not-supported`. Two emitters each covering 50 of 100 scenarios, with 25 shared successes,
+produce **75%** combined coverage. Counts follow the selected tier and use each table's reports;
+equally named scenarios in different tables/spec sets remain separate.
+
+Groups and emitter rows follow the configured order; ungrouped emitters keep separate cards
+afterward. `emitterDisplayNames` controls row and table labels without affecting grouping.
+These options are also available on `DashboardFromAzureStorage`'s `options` and do not change
+table columns or report loading.
+
 ## Dev
 
 ```bash

packages/spec-dashboard/src/apis.ts

@@ -19,6 +19,13 @@ export interface TableDefinition {
   emitterNames?: string[];
 }
 
+export interface EmitterGroup {
+  /** Overview card label. */
+  readonly name: string;
+  /** Emitter package names, in display order. */
+  readonly emitters: readonly string[];
+}
+
 export interface CoverageFromAzureStorageOptions {
   readonly storageAccountName: string;
   readonly containerName: string;
@@ -34,6 +41,11 @@ export interface CoverageFromAzureStorageOptions {
   readonly showOverview?: boolean;
   /** Optional friendly display names for emitters. Key is the emitter package name, value is the display name. */
   readonly emitterDisplayNames?: Readonly<Record<string, string>>;
+  /**
+   * Overview groups in display order. Count each scenario once per table, covered if any member covers it.
+   * Does not change table columns or report loading.
+   */
+  readonly groupEmitters?: readonly EmitterGroup[];
 }
 
 export interface GeneratorCoverageSuiteReport extends CoverageReport {

packages/spec-dashboard/src/components/coverage-overview.module.css

@@ -18,7 +18,13 @@
   gap: 16px;
 }
 
+.overview {
+  display: flex;
+  min-width: 0;
+}
+
 .card {
+  flex: 1;
   background-color: var(--colorNeutralBackground1);
   padding: 16px 16px 20px;
   text-align: center;
@@ -27,6 +33,7 @@
   align-items: center;
   gap: 4px;
   min-height: 100px;
+  min-width: 0;
 }
 
 .card-name {
@@ -35,4 +42,35 @@
   display: flex;
   align-items: center;
   text-align: center;
+  overflow-wrap: anywhere;
+}
+
+.emitters {
+  align-self: stretch;
+  margin: 8px 0 0;
+  padding-top: 8px;
+  border-top: 1px solid var(--colorNeutralStroke2);
+  display: flex;
+  flex-direction: column;
+  gap: 6px;
+}
+
+.emitter-row {
+  display: flex;
+  align-items: baseline;
+  justify-content: space-between;
+  gap: 8px;
+}
+
+.emitter-name {
+  min-width: 0;
+  color: var(--colorNeutralForeground2);
+  text-align: left;
+  overflow-wrap: anywhere;
+}
+
+.emitter-percentage {
+  margin: 0;
+  flex-shrink: 0;
+  font-variant-numeric: tabular-nums;
 }