chore: migrate from ESLint/Prettier to Biome for linting and formatting

Author: tyler-dane

.husky/pre-commit

@@ -111,8 +111,8 @@ Run `bun run test:core`, `bun run test:web`, and `bun run test:backend` after ma
 
 ### Linting
 
-- Run `./node_modules/.bin/eslint <changed app files>` before finishing. Treat eslint as required validation for changed implementation files, not an optional follow-up.
-- `bunx prettier . --write`
+- Run `bun run lint` before finishing. Treat Biome lint and format checks as required validation for changed implementation files, not an optional follow-up.
+- Run `bun run lint:fix` to apply safe Biome fixes and formatting.
 
 ## Validation
 
@@ -177,14 +177,14 @@ packages/core/src/
 
 1. **Start Development**: `bun run dev:web` (frontend only, always works)
 2. **Run Tests**: `bun run test:core && bun run test:web` (add `&& bun run test:backend` when credentials available)
-3. **Run Eslint On Changed Implementation Files**: `./node_modules/.bin/eslint <changed app files>`
-4. **Check Code Style**: `bunx prettier . --write`
+3. **Run Biome Lint and Format Checks**: `bun run lint`
+4. **Apply Safe Fixes When Needed**: `bun run lint:fix`
 5. **Manual Validation**: Open <http://localhost:9080/> and verify login page loads
 
 ## Cursor Cloud specific instructions
 
 - Prefer running scoped checks for changed areas: `bun run test:core`, `bun run test:web`, `bun run test:backend`, or `bun run test:scripts` as applicable.
-- Run `./node_modules/.bin/eslint <changed app files>` before handing off work.
+- Run `bun run lint` before handing off work.
 - Do not run `bun run test` in restricted environments unless explicitly required.
 - For UI-affecting changes in `packages/web`, validate with `bun run dev:web` and confirm behavior in the web dev server.
 - If backend work is required, ensure `packages/backend/.env.local` exists by copying `packages/backend/.env.local.example`.
@@ -210,7 +210,7 @@ packages/core/src/
 - **Backend won't start**: Missing environment variables in `packages/backend/.env.local`, use web-only development (`bun run dev:web`)
 - Environment: Copy from `packages/backend/.env.local.example` to `packages/backend/.env.local` (there is no `.env.example`).
 - Webpack dev server warns about a missing `.env.local` file; this is harmless—it falls back to `process.env`.
-- Husky pre-push hook runs `bunx prettier . --write`, which can modify files. Ensure working tree is clean or committed before pushing.
+- Biome can modify files when run with `bun run lint:fix`. Review the diff before pushing.
 
 ### Network Limitations
 
@@ -314,9 +314,9 @@ packages/core/src/
 
 ### Pre-commit Validation
 
-The repository includes Husky hooks that will:
+Before committing or pushing:
 
-- Run `bunx lint-staged` on pre-commit (formats code with Prettier)
-- Run `bunx prettier . --write` on pre-push (ensures consistent formatting)
+- Run `bun run lint` to check lint, formatting, and import organization with Biome.
+- Run `bun run lint:fix` when you want Biome to apply safe fixes.
 
 **ALWAYS** ensure your commits pass these checks before pushing.

.husky/pre-push

@@ -13,7 +13,7 @@ Run after making changes. Always run `bun run type-check` before handoff.
 | `packages/backend` only      | `bun run test:backend`                                                                |
 | `packages/scripts` only      | `bun run test:scripts`                                                                |
 | Cross-package (types/schema) | `bun run test:core && bun run test:web && bun run test:backend && bun run type-check` |
-| Lint changed files           | `./node_modules/.bin/eslint <file1> <file2>`                                          |
+| Lint and format check        | `bun run lint`                                                                        |
 
 Or use the smart detect-and-run script: **`bun run verify`** (checks git diff, runs the right suites + type-check).
 

.prettierignore

@@ -82,7 +82,7 @@ bun run test:e2e
 
 # Type checking and linting
 bun run type-check
-bunx prettier . --write
+bun run lint
 ```
 
 ## Contributing

.prettierrc

@@ -0,0 +1,146 @@
+{
+  "$schema": "https://biomejs.dev/schemas/2.4.12/schema.json",
+  "vcs": {
+    "enabled": true,
+    "clientKind": "git",
+    "useIgnoreFile": true
+  },
+  "formatter": {
+    "enabled": true,
+    "indentStyle": "space",
+    "indentWidth": 2,
+    "lineWidth": 80
+  },
+  "css": {
+    "parser": {
+      "tailwindDirectives": true
+    }
+  },
+  "linter": {
+    "enabled": true,
+    "rules": {
+      "recommended": true,
+      "a11y": {
+        "noNoninteractiveElementToInteractiveRole": "warn",
+        "noNoninteractiveTabindex": "warn",
+        "noPositiveTabindex": "warn",
+        "noRedundantRoles": "warn",
+        "noStaticElementInteractions": "warn",
+        "noSvgWithoutTitle": "warn",
+        "useAriaPropsForRole": "warn",
+        "useAriaPropsSupportedByRole": "warn",
+        "useButtonType": "warn",
+        "useFocusableInteractive": "warn",
+        "useHtmlLang": "warn",
+        "useSemanticElements": "warn",
+        "useValidAriaRole": "warn"
+      },
+      "correctness": {
+        "noUnreachable": "warn",
+        "useExhaustiveDependencies": "warn",
+        "useHookAtTopLevel": "warn",
+        "useYield": "warn"
+      },
+      "style": {
+        "useImportType": {
+          "level": "warn",
+          "options": {
+            "style": "inlineType"
+          }
+        }
+      },
+      "suspicious": {
+        "noArrayIndexKey": "warn",
+        "noAssignInExpressions": "warn",
+        "noConsole": "off",
+        "noDoubleEquals": "warn",
+        "noDuplicateTestHooks": "warn",
+        "noExportsInTest": "warn",
+        "useIterableCallbackReturn": "warn"
+      },
+      "nursery": {
+        "useSortedClasses": {
+          "level": "warn",
+          "options": {
+            "attributes": ["className", "class"],
+            "functions": ["clsx", "classnames", "cn"]
+          }
+        }
+      }
+    }
+  },
+  "assist": {
+    "actions": {
+      "source": {
+        "organizeImports": {
+          "level": "on",
+          "options": {
+            "groups": [
+              [":BUN:", ":NODE:"],
+              ":PACKAGE:",
+              ["@core/**", "!@core"],
+              ["@web/**", "!@web"],
+              ["@backend/**", "!@backend"],
+              ":PATH:"
+            ]
+          }
+        }
+      }
+    }
+  },
+  "overrides": [
+    {
+      "includes": ["packages/web/**/*.ts", "packages/web/**/*.tsx"],
+      "linter": {
+        "rules": {
+          "suspicious": {
+            "noConsole": {
+              "level": "warn",
+              "options": {
+                "allow": ["warn", "error"]
+              }
+            }
+          }
+        }
+      }
+    },
+    {
+      "includes": [
+        "**/__tests__/**",
+        "**/*.test.ts",
+        "**/*.test.tsx",
+        "**/*.spec.ts",
+        "**/*.spec.tsx"
+      ],
+      "linter": {
+        "rules": {
+          "suspicious": {
+            "noConsole": "off"
+          }
+        }
+      }
+    },
+    {
+      "includes": ["**/*.js", "**/*.mjs", "**/*.cjs"],
+      "linter": {
+        "rules": {
+          "style": {
+            "useImportType": "off"
+          }
+        }
+      }
+    }
+  ],
+  "files": {
+    "ignoreUnknown": true,
+    "includes": [
+      "**",
+      "!build",
+      "!coverage",
+      "!logs",
+      "!node_modules",
+      "!*.min.js",
+      "!bun.lock"
+    ]
+  }
+}