endpoint imports node:fs via digest/tree.ts, breaking the Cloudflare adapter

[hev]

Problem

The endpoint bundle pulls in node:fs, which workerd only provides under the
nodejs_compat compatibility flag. On a stock @astrojs/cloudflare site the
module fails to resolve and the whole site 500s — not just /api/ask, since the
dev server can't build the route:

[vite]: Rolldown failed to resolve import "node:fs"
  (resolved id: node:fs) in @hevmind/ask/src/digest/tree.ts.

astro build warns about the same thing more quietly:

[WARN] [vite] Unexpected Node.js imports for environment "prerender".
Do you need to enable the "nodejs_compat" compatibility flag?

Cause

endpoint.ts:12
statically imports from the digest tree module:

import { digestTreeFiles } from './digest/tree.ts';

and tree.ts:1
imports fs at module top level:

import { readFileSync, readdirSync, statSync } from 'node:fs';
import path from 'node:path';

Why this one is easy

digestTreeFiles doesn't use fs at all. It's pure — it takes an in-memory
Digest and renders it to DigestTreeFile[]
(tree.ts:74),
and the endpoint hands it the digest it already got from the
virtual:hev-ask/digest module, not from disk
(endpoint.ts:201).

Every actual fs caller in that file is build-time or CLI only:

Function	Uses fs	Called from
digestTreeFiles	no	the endpoint (worker)
renderMetaFile, renderNodeFile, nodePath, …	no	digestTreeFiles
readDigestArtifact	statSync	integration.ts (Node)
readDigestTree	readFileSync	Node
readLegacyJson	readFileSync	Node
walk	readdirSync	Node

So the worker is paying for a Node dependency it never calls. It's purely an
import-graph artifact.

Fix

Split the module along the line that already exists:

• digest/tree-render.ts — the pure serializers (digestTreeFiles and the
  render* / *Path helpers). No node:fs, no node:path.
• digest/tree.ts — keeps the fs readers, imports the pure module.

The endpoint then imports only tree-render.ts and the worker bundle has no
Node builtins from this path. No behavior change, no nodejs_compat needed, and
it keeps ask digest bundle / the tarball route working as-is.

node:path usage in the pure helpers (if any survive the split) should become
plain string joins — it's all POSIX-style digest-relative paths.

Note

Telling users to enable nodejs_compat would also make the error go away, but
it's the wrong fix: it papers over a Node dependency in worker code that isn't
needed, and it's an extra config step on the path we advertise as turnkey.

---

Found while wiring 0.3.4 into a Starlight docs site. Present on main
(a3204b4), not just the 0.3.4 tag. Fixing this alone is not sufficient to get
the Cloudflare path working — #3 is waiting immediately
behind it.