fix(fluid-build): shared eslint-config-fluid files to EsLintTask cache invalidation (#25997)

## Description

ESLint config changes in the shared
`@fluidframework/eslint-config-fluid` package were not properly
invalidating the eslint task because only the local config file was
tracked.

Extended `configFileFullPaths` in `EsLintTask` to include files from the
shared config:

- **Shared config tracking**: Tracks key files from
`@fluidframework/eslint-config-fluid` (index.js, base.js, strict.js,
recommended.js, minimal-deprecated.js, strict-biome.js, package.json) as
additional config files
- **Graceful handling**: Uses a path relative to the repo root
(`common/build/eslint-config-fluid`); if the directory doesn't exist,
gracefully skips this tracking

This keeps `EsLintTask` as a `TscDependentTask` while adding the
additional config file tracking needed to properly invalidate when
shared configs change.

## Reviewer Guidance

The change preserves existing behavior and simply extends
`configFileFullPaths` to include additional files. `TsLintTask` remains
unchanged.

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: tylerbutler <19589+tylerbutler@users.noreply.github.com>

Author: tylerbutler

build-tools/packages/build-tools/src/fluidBuild/tasks/leaf/lintTasks.ts

@@ -3,9 +3,19 @@
  * Licensed under the MIT License.
  */
 
+import { existsSync } from "node:fs";
+import path from "node:path";
+
 import { getEsLintConfigFilePath, getInstalledPackageVersion } from "../taskUtils";
 import { TscDependentTask } from "./tscTask";
 
+/**
+ * Path to the shared eslint-config-fluid package relative to the repo root.
+ * Can be overridden with the FLUID_BUILD_ESLINT_CONFIG_PATH environment variable.
+ */
+const sharedEslintConfigPath =
+	process.env.FLUID_BUILD_ESLINT_CONFIG_PATH ?? "common/build/eslint-config-fluid";
+
 export class TsLintTask extends TscDependentTask {
 	protected get configFileFullPaths() {
 		return [this.getPackageFileFullPath("tslint.json")];
@@ -18,14 +28,67 @@ export class TsLintTask extends TscDependentTask {
 
 export class EsLintTask extends TscDependentTask {
 	private _configFileFullPath: string | undefined;
+	private _sharedConfigFiles: string[] | undefined;
+
+	/**
+	 * Gets the absolute paths to shared eslint config files that should be tracked.
+	 * These are files from @fluidframework/eslint-config-fluid that affect linting behavior.
+	 */
+	private getSharedConfigFiles(): string[] {
+		if (this._sharedConfigFiles !== undefined) {
+			return this._sharedConfigFiles;
+		}
+
+		const sharedDir = path.join(this.context.repoRoot, sharedEslintConfigPath);
+
+		// If the shared config directory doesn't exist, skip tracking
+		if (!existsSync(sharedDir)) {
+			console.warn(
+				`Warning: Shared ESLint config directory not found at ${sharedDir}. ` +
+					`ESLint cache invalidation may not work correctly if shared config changes.`,
+			);
+			this._sharedConfigFiles = [];
+			return this._sharedConfigFiles;
+		}
+
+		// Track the main config files from the shared eslint-config-fluid package
+		const sharedConfigFiles = [
+			"index.js",
+			"base.js",
+			"strict.js",
+			"recommended.js",
+			"minimal-deprecated.js",
+			"strict-biome.js",
+			"package.json", // Tracks version changes
+		];
+
+		const files: string[] = [];
+		for (const file of sharedConfigFiles) {
+			const fullPath = path.join(sharedDir, file);
+			if (existsSync(fullPath)) {
+				files.push(fullPath);
+			} else {
+				console.warn(
+					`Warning: Expected shared ESLint config file not found: ${fullPath}. ` +
+						`ESLint cache invalidation may not work correctly.`,
+				);
+			}
+		}
+
+		this._sharedConfigFiles = files;
+		return this._sharedConfigFiles;
+	}
+
 	protected get configFileFullPaths() {
 		if (!this._configFileFullPath) {
 			this._configFileFullPath = getEsLintConfigFilePath(this.package.directory);
 			if (!this._configFileFullPath) {
 				throw new Error(`Unable to find config file for eslint ${this.command}`);
 			}
 		}
-		return [this._configFileFullPath];
+
+		// Include local config file and shared eslint-config-fluid files
+		return [this._configFileFullPath, ...this.getSharedConfigFiles()];
 	}
 
 	protected get useWorker() {