feat: --cwd flag + linear-memory hash cache

[maastrich]

Summary

Two commits, shipping together as 0.7.0.

feat(cli): add --cwd flag

Run hashup as if from the given directory. Changes where hashup.json is discovered, where relative entry/extras paths resolve, and where --out writes. Defaults to process.cwd().

hashup --cwd ./packages/app
hashup --cwd ./packages/app src/index.ts -o ../dist/app.hash

perf: linear-memory hash cache

HashupCache.hashes now stores each file's own content hash (one 64-char sha256 string) instead of the flattened transitive list. The transitive contribution is reconstructed at combine time by walking cache.deps. Memory drops from O(files × avg closure) to O(unique files).

Measured on a real-world 81-entry glob against a large shared UI graph (bfront webapps/lcm):

Metric	0.6.0 (flattened)	New (linear)
Peak RSS	~9.3 GB	125 MB
Wall time	~3 min	1.1 s
Heap flag	needed --max-old-space-size=12288	default 4 GB

~74× less memory, ~160× faster.

Hash output changes. Final digest is now sha256(each reachable file's hash, concatenated in sorted-path order). Every unique file contributes exactly once regardless of how many import paths reach it. Any stored 0.6.x hashes must be re-baselined. Side benefit: cycles now hash the same regardless of which member was the entry point (test strengthened to assert this).

Targeted break for direct hashFile callers. Return type is now Promise<string | null> instead of Promise<string[]>. hashup() itself is unchanged — the option surface is additive.

Test plan

• vp test — 117/117 passing
• vp check clean
• Inline snapshot in tests/examples.test.ts updated to the new algorithm's output
• tests/circular.test.ts strengthened: same hash from any cycle member
• Verified against the bfront config that OOM'd 0.6.0 — now completes in ~1 s with 125 MB
• shared-cache.test.ts still passes (shared-cache determinism holds under the new algorithm)

Docs

Updated docs/api/hashup.md, docs/api/utilities.md, docs/guide/how-it-works.md, docs/guide/cli.md (new --cwd option, new algorithm description, caveats refreshed).

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[github-actions]

📖 Docs preview: https://maastrich.github.io/hashup/branches/pr-19/