build(git-sync): land the @docmost/git-sync package into develop, code-only (#326 step 1 / PR-A)

The git-sync converter + engine source lived only on the #119 branch; develop
had just the dead compiled build/. Bring the whole package (src + ~700 tests)
onto develop under CI, with NO consumer wired — git-sync stays fully inert in
develop (nothing in apps/server imports it), so runtime behavior is unchanged.
This unblocks #293 (extract the shared converter package from the landed source)
and lets #119's functionality land LAST, already writing the canonical format
(per the #326 landing order).

- packages/git-sync: src (lib converter + engine) + test corpus + configs.
- Remove develop's dead committed packages/git-sync/build/; gitignore it
  (built in CI/Docker via pnpm build, never committed — no src/build drift).
- pnpm-lock.yaml: add the @docmost/git-sync importer (a missing workspace
  package in the lock is a CI blocker). `pnpm install --frozen-lockfile` passes.
- NO server integration / loader / Dockerfile runtime changes (those come with
  #119 at step 6).

Verified: tsc clean; vitest 711 passed | 1 expected-fail, 0 failures, 0 type
errors; pnpm --frozen-lockfile EXIT 0; apps/server has no git-sync import.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

packages/git-sync/src/engine/sanitize.ts

@@ -0,0 +1,109 @@
+/**
+ * Deterministic filename strategy (SPEC §12).
+ *
+ * The file name is COSMETIC — the source of truth for the file<->page link is
+ * `pageId` / `slugId` inside the meta block, so renaming a file is safe. These
+ * functions are intentionally dependency-free and pure, so they are trivially
+ * unit-testable.
+ */
+
+// Printable characters forbidden in file names on common filesystems (mainly
+// Windows): / \ < > : " | ? *. Each match is replaced with a single "-".
+// Spaces are NOT in this set; whitespace is normalized separately below.
+// ASCII control characters (code points 0..31) are stripped in a separate pass
+// (see stripControlChars) to keep this literal free of embedded control bytes.
+const FORBIDDEN_PRINTABLE_RE = /[/\\<>:"|?*]/g;
+
+// Runs of whitespace (including tabs/newlines) collapse to a single space.
+const WHITESPACE_RUN_RE = /\s+/g;
+
+// Reserved Windows device names (case-insensitive). A bare match (with or
+// without an extension) is unusable as a file name, so it is prefixed with "_".
+const RESERVED_WINDOWS_NAMES = new Set([
+  "con",
+  "prn",
+  "aux",
+  "nul",
+  "com1",
+  "com2",
+  "com3",
+  "com4",
+  "com5",
+  "com6",
+  "com7",
+  "com8",
+  "com9",
+  "lpt1",
+  "lpt2",
+  "lpt3",
+  "lpt4",
+  "lpt5",
+  "lpt6",
+  "lpt7",
+  "lpt8",
+  "lpt9",
+]);
+
+// Cap on the sanitized length to stay well within filesystem path-component
+// limits (255 bytes on most FSes) while leaving room for an extension and a
+// disambiguation suffix.
+const MAX_LENGTH = 120;
+
+/**
+ * Replace every ASCII control character (code points 0..31) with "-". Done by
+ * scanning code points rather than a control-range regex literal, so the source
+ * file carries no embedded control bytes.
+ */
+function stripControlChars(input: string): string {
+  let out = "";
+  for (let i = 0; i < input.length; i++) {
+    out += input.charCodeAt(i) < 32 ? "-" : input[i];
+  }
+  return out;
+}
+
+/**
+ * Sanitize a page title into a safe file-name component (WITHOUT extension).
+ *
+ * Steps: replace forbidden / control characters with "-", collapse whitespace
+ * runs to a single space, trim, cap the length, then guard against an empty
+ * result, an all-dots result, or a reserved Windows device name by prefixing
+ * with "_".
+ */
+export function sanitizeTitle(title: string): string {
+  let name = stripControlChars(title ?? "")
+    .replace(FORBIDDEN_PRINTABLE_RE, "-")
+    .replace(WHITESPACE_RUN_RE, " ")
+    .trim();
+
+  if (name.length > MAX_LENGTH) {
+    name = name.slice(0, MAX_LENGTH).trim();
+  }
+
+  // Compare the base name (before the first dot) against reserved names, so
+  // both "CON" and "con.md" are caught.
+  const base = name.split(".")[0]?.toLowerCase() ?? "";
+  // A name that is empty, consists only of dots ("." / ".." / "..."), or is a
+  // reserved Windows device name is unusable as a path component. The all-dots
+  // case is a path-traversal hazard in particular: an unprefixed ".." would
+  // become a parent-directory segment and let a page escape the vault, so it
+  // MUST be neutralized here (becomes "_..", which is a literal file name).
+  if (
+    name.length === 0 ||
+    /^\.+$/.test(name) ||
+    RESERVED_WINDOWS_NAMES.has(base)
+  ) {
+    name = "_" + name;
+  }
+
+  return name;
+}
+
+/**
+ * Disambiguate a sanitized name when two siblings in the same folder collapse
+ * to the same name. Appends a stable suffix built from the page's `slugId`, so
+ * the result stays deterministic across runs (SPEC §12: `Title ~slugId`).
+ */
+export function disambiguate(name: string, slugId: string): string {
+  return `${name} ~${slugId}`;
+}