build: add prettier tooling and formatting config

.gitattributes

@@ -0,0 +1,15 @@
+# Prettier's endOfLine default is "lf" and CI runs on Linux. Git for Windows
+# ships core.autocrlf=true in its system config, so without this a fresh Windows
+# clone gets CRLF working files and `npm run format:check` flags every file.
+* text=auto eol=lf
+
+# Binary assets: never touch.
+*.png binary
+*.jpg binary
+*.jpeg binary
+*.gif binary
+*.ico binary
+*.zip binary
+*.woff binary
+*.woff2 binary
+*.ttf binary

.prettierignore

@@ -0,0 +1,19 @@
+# Prettier does not read .gitignore, so the build output is repeated here.
+unpacked/
+dist/
+coverage/
+test-results/
+playwright-report/
+
+# npm rewrites this on every install, with its own formatting.
+package-lock.json
+
+# Regenerated wholesale by git-cliff / release-please on every release.
+CHANGELOG.md
+
+# Captured bexio pages: the jsdom and Playwright tests read DOM and text out of
+# these, and two of them do not parse as HTML at all. _raw holds unscrubbed
+# captures (git-ignored). tiny.html is a hand-written entity/whitespace probe.
+packages/chrome-extension/test/fixtures/bexio/*.html
+packages/chrome-extension/test/fixtures/bexio/_raw/
+packages/chrome-extension/test/support/__inline__/tiny.html

.vscode/extensions.json

@@ -0,0 +1,3 @@
+{
+  "recommendations": ["esbenp.prettier-vscode"]
+}

.vscode/settings.json

@@ -1,4 +1,37 @@
 {
     "editor.acceptSuggestionOnEnter": "on",
-    "typescript.tsdk": "node_modules\\typescript\\lib"
+    "typescript.tsdk": "node_modules\\typescript\\lib",
+    "editor.formatOnSave": true,
+    // Prettier is scoped per language on purpose. A global "editor.defaultFormatter"
+    // would also claim Build.ps1 / CreateRelease.ps1, which Prettier cannot format.
+    "[typescript]": {
+        "editor.defaultFormatter": "esbenp.prettier-vscode"
+    },
+    "[typescriptreact]": {
+        "editor.defaultFormatter": "esbenp.prettier-vscode"
+    },
+    "[javascript]": {
+        "editor.defaultFormatter": "esbenp.prettier-vscode"
+    },
+    "[json]": {
+        "editor.defaultFormatter": "esbenp.prettier-vscode"
+    },
+    "[jsonc]": {
+        "editor.defaultFormatter": "esbenp.prettier-vscode"
+    },
+    "[markdown]": {
+        "editor.defaultFormatter": "esbenp.prettier-vscode"
+    },
+    "[yaml]": {
+        "editor.defaultFormatter": "esbenp.prettier-vscode"
+    },
+    "[html]": {
+        "editor.defaultFormatter": "esbenp.prettier-vscode"
+    },
+    "[css]": {
+        "editor.defaultFormatter": "esbenp.prettier-vscode"
+    },
+    "[scss]": {
+        "editor.defaultFormatter": "esbenp.prettier-vscode"
+    }
 }

docs/superpowers/specs/2026-08-05-prettier-format-sweep-design.md

@@ -0,0 +1,163 @@
+# Design — repo-wide Prettier format sweep
+
+**Date:** 2026-08-05
+**Status:** approved for implementation
+
+## Problem
+
+A `.prettierrc` (`tabWidth: 2`, `useTabs: false`, `printWidth: 120`) has been checked in for a
+long time, but Prettier itself was never installed — not at the repo root, not in any workspace.
+The config was therefore only ever honoured by whatever editor happened to have the Prettier
+extension enabled, which is why formatting drifted file by file and why `.vscode/settings.json`
+(4-space) and `.prettierrc` (2-space) disagree with each other.
+
+The goal is to make the checked-in config real: pin Prettier, give it an ignore list, make line
+endings deterministic, format the repo once, and then keep it formatted in CI.
+
+## Scope
+
+Measured on `origin/main` at `eebd7db` with the `.prettierignore` below in place and an LF working
+tree, `npm run format:check` reports **108 files**:
+
+| Type                  | Count |
+| --------------------- | ----- |
+| `.ts`                 | 65    |
+| `.md`                 | 17    |
+| `.json`               | 9     |
+| `.tsx`                | 7     |
+| `.css`                | 4     |
+| `.js`                 | 2     |
+| `.yml`                | 1     |
+| `.html`               | 1     |
+| `.prettierrc`         | 1     |
+| `.markdownlint.jsonc` | 1     |
+| **Total**             | 108   |
+
+The exact number will move as feature work lands; it is a snapshot, not a contract. What matters
+is that the set is "every checked-in file Prettier understands, minus the exclusions below".
+
+### Provenance of the earlier "180 / 173 files" figures
+
+An earlier pass quoted 180 unformatted files before the ignore list and 173 after it. Both numbers
+are reproducible, but not on this branch point:
+
+- They were measured at commit `e06f6c2` (tip of `claude/prepare-format-120-files-f8497b`), two
+  commits behind `origin/main`.
+- More importantly, they were measured on a **CRLF working tree**. Git for Windows ships
+  `core.autocrlf=true` in its system config, so a fresh Windows checkout gets CRLF working files
+  while the index stays LF. Prettier's `endOfLine` default is `"lf"`, so on such a checkout it
+  flags _every_ file it can parse, whether or not anything else about it is wrong. That is why the
+  old breakdown listed all 101 `.ts` files of that commit rather than a subset.
+
+At `e06f6c2` there are exactly 182 files Prettier can match; two of them fail to parse, leaving
+180 warnings and exit code 2 — the reported baseline, to the file. The `.gitattributes` added in
+Phase A is what removes this whole class of confusion: with `* text=auto eol=lf` a Windows checkout
+gets LF working files, and local `format:check` finally agrees with CI.
+
+### Excluded
+
+| File                                                          | Reason                                                                                                                                                                  |
+| ------------------------------------------------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
+| `package-lock.json`                                           | npm rewrites it on every install with its own formatting, so a formatted version would make the check permanently red                                                   |
+| `CHANGELOG.md`                                                | regenerated wholesale by git-cliff / release-please; a formatted version does not survive a release and conflicts with the Release PR, which stays open by project rule |
+| `packages/chrome-extension/test/fixtures/bexio/*.html`        | captured bexio pages; the jsdom and Playwright tests read DOM and text out of them, and `kb_invoice-show.html` + `monitoring-list.html` do not parse as HTML at all     |
+| `packages/chrome-extension/test/support/__inline__/tiny.html` | hand-written DOM probe for HTML entities, same reasoning as the fixtures                                                                                                |
+
+The two unparseable fixtures are also what made the un-ignored run exit with code **2** rather than
+**1**: Prettier reports a parse error separately from a formatting difference. Ignoring them brings
+the exit code back to a plain 1, so a future CI step fails for the one reason it is meant to.
+
+Build output (`unpacked/`, `dist/`) and test output (`coverage/`, `test-results/`,
+`playwright-report/`) are ignored as well. Prettier 3 does **not** read `.gitignore`, so on a
+machine that has built the project those directories would otherwise be formatted.
+
+### Deliberately not excluded
+
+`packages/chrome-extension/public/manifest.json` and `.release-please-manifest.json` are generated
+in part, but `updateManifest.js` edits them (and `package.json`) by regex replacement rather than
+by `JSON.parse` → `JSON.stringify`. It therefore preserves surrounding formatting, and a formatted
+version of these files survives a release untouched. They stay in the sweep.
+
+## Tooling (Phase A)
+
+1. **Pin Prettier.** `npm install -D prettier@3.9.6` at the repo root. `.npmrc` sets
+   `save-exact=true`, so the entry lands as `"prettier": "3.9.6"` with no caret — matching the
+   repo's rule that every dependency version is pinned. This is the one intended change to
+   `package-lock.json`; CLAUDE.md's "use `npm ci`, not `npm i`" rule is about worktrees not
+   perturbing the lockfile, and here the lockfile change is the point.
+
+2. **Scripts.** `format` (`prettier --write .`) and `format:check` (`prettier --check .`) in the
+   root `package.json`, immediately after `typecheck`.
+
+3. **`.prettierignore`.** The exclusions above plus the build/test output directories.
+
+4. **`.gitattributes`.** `* text=auto eol=lf`, plus `binary` for the image/font/zip assets. The
+   index is already 100% LF (`git ls-files --eol`), so adding it produces zero content diff — it
+   only fixes what a _checkout_ writes to disk. There are no `.bat`/`.cmd`/`.sh` files in the repo,
+   so nothing needs CRLF; the two PowerShell scripts are fine with LF.
+
+5. **Editor wiring.** `editor.formatOnSave` plus a per-language `editor.defaultFormatter` of
+   `esbenp.prettier-vscode` for `typescript`, `typescriptreact`, `javascript`, `json`, `jsonc`,
+   `markdown`, `yaml`, `html`, `css` and `scss`, and a `.vscode/extensions.json` recommending the
+   extension. The formatter is set **per language on purpose**: a global
+   `editor.defaultFormatter` would hijack `.ps1` files, and this repo has `Build.ps1` and
+   `CreateRelease.ps1`, which Prettier cannot format.
+
+`eslint-config-prettier` is **not** added. The only ESLint config in the repo
+(`packages/sidePanel-import/eslint.config.js`) contains no stylistic rules, so there is nothing for
+it to turn off. No pre-commit hook framework is added either — the repo has none today, and CI plus
+format-on-save covers the same ground without a new dependency in everyone's commit path.
+
+## Sequencing
+
+The work is split into two phases so that the mechanical 100+-file diff never sits in the same
+commit as anything reviewable.
+
+**Phase A — tooling only.** Everything under "Tooling" above, in two commits:
+
+- `docs: design for the repo-wide prettier format sweep`
+- `build: add prettier tooling and formatting config`
+
+No file is reformatted and no CI step is added, so Phase A has zero conflict risk and can merge at
+any time. `npm run format:check` fails by design after Phase A; that is the point of Phase B.
+
+**Phase B — the sweep, once the tree is quiet.** Two further commits:
+
+- `style: format repo with prettier` — the output of a single `npm run format`, nothing else. A
+  formatting-only commit, so it can be reviewed by confirming the diff is whitespace and that the
+  test suite still passes.
+- `ci: enforce prettier formatting` — adds a `npm run format:check` step to
+  `.github/workflows/node.js.yml` (next to `Typecheck`) and records the sweep's SHA in
+  `.git-blame-ignore-revs`, so `git blame` skips straight past it.
+
+`.git-blame-ignore-revs` cannot be written before Phase B, because it needs the sweep commit's own
+SHA.
+
+`style:` and `ci:` are both configured as `hidden` in `release-please-config.json`, so a
+100+-file cosmetic commit and the CI step stay out of the generated release notes.
+
+### Why Phase B waits
+
+A repo-wide reformat conflicts with every open branch that touches a formatted file. At time of
+writing the unmerged work is `claude/bexio-extension-issue-12-4ad9db` — three commits on top of
+what already landed via #127, all of them inside
+`packages/sidePanel-import/src/components/ImportEntries/`, which is squarely in the sweep's path.
+
+Phase B is therefore gated on that work landing on `main`. The resolution for any branch that is
+still open when the sweep lands is always the same: rebase onto `main` and re-run `npm run format`,
+which turns a whitespace conflict back into a mechanical no-op.
+
+## Verification (Phase B)
+
+Run in order, on a checkout that has had `.gitattributes` applied:
+
+1. `npm run format:check` — must exit 0.
+2. `npm run typecheck` — must pass.
+3. `npm test` — the Vitest suite, including the slow build smoke test that shells out to
+   `Build.ps1`.
+4. `npm run test:e2e` — the Playwright extension smoke + behaviour specs.
+
+Steps 3 and 4 are the actual evidence that the sweep was semantically neutral. A formatting diff is
+easy to eyeball but tedious to prove correct by reading; the DOM-dependent tests and the real
+Chromium run are what confirm that nothing in the fragile `trigger*` / selector layer changed
+meaning.

package.json

@@ -27,7 +27,9 @@
         "test:fast": "vitest run --exclude \"**/*.slow.test.ts\"",
         "test:watch": "vitest",
         "test:e2e": "playwright test --config e2e/playwright.config.ts",
-        "typecheck": "npm run typecheck --workspaces --if-present"
+        "typecheck": "npm run typecheck --workspaces --if-present",
+        "format": "prettier --write .",
+        "format:check": "prettier --check ."
     },
     "repository": {
         "type": "git",
@@ -53,6 +55,7 @@
         "fs-extra": "11.4.0",
         "git-cliff": "2.13.1",
         "jsdom": "30.0.1",
+        "prettier": "3.9.6",
         "vite": "8.2.0",
         "vitest": "4.1.10"
     },