open-design/tools/pack/CACHE.md

tools-pack build cache contract

This file is the source of truth for the tools-pack build-graph cache: the cache under --cache-dir that stores packaged build artifacts as content-addressed nodes. Read it before changing any node key, adding a node, or changing what a node writes.

It records current state only, not change history — same convention as specs/current/ci.md.

Out of scope: the GitHub Actions cache that wraps this store. That layer is owned by .github/; it restores and saves the store as an opaque directory and carries no correctness obligation (see Why coarse restore is safe below).

Cache model

A node is { id, key, outputs, build, invalidate }, acquired through ToolPackCache (src/cache.ts).

• keyHash = hash(node.id + "\n" + node.key); the entry lives at entries/<node.id>/<keyHash>/ with a manifest.json.
• An entry is accepted only when manifest.key === node.key exactly. A mismatch is reported as key mismatch and the node rebuilds (cache.ts:270-282). There is no fuzzy or prefix matching inside the store.
• invalidate is an additional per-node veto applied to an otherwise-valid entry (for example win.packaged-app re-validates its native rebuild output).
• materialize copies entry outputs to their workspace locations. Steps that run on the materialization path execute on both the hit and the miss path.

Why coarse restore is safe

Because acceptance is an exact node.key comparison, a restored store is a pool of candidates, not an authority. Entries that do not match are ignored. An outer layer may therefore restore a broader or older store than strictly requested without risking a wrong build — it only affects how much work is skipped, never what is produced.

This property is what the surrounding CI caching depends on. Do not weaken it by introducing prefix or best-effort matching inside the store.

Node inventory

The build-graph cache is almost entirely Windows-specific.

Node	Platform
<platform>.workspace-build	all
win.resource-tree	win
win.workspace-tarballs	win
win.packaged-app	win
win.electron-builder-dir	win
win.nsis-payload-base	win
win.nsis-payload-overlay	win
win.nsis-installer	win
win.portable-zip	win
win.launcher-payload-base	win
win.launcher-payload	win

mac and linux have <platform>.workspace-build only.

The workspace build delegates Web type validation to independent same-commit CI/release checks (next typegen plus the full Web tsconfig, including tests). The build recipe explicitly sets OD_WEB_TYPECHECK=external; this recipe is part of the workspace node key. Local ordinary next build still checks its production-only tsconfig. Declaration outputs remain part of the cache contract.

Determinant rules

R1 — A node key must cover every input that determines the node's output. Inputs include file content, configuration values, tool versions, and process environment. An input that is read by build but absent from key is a defect, not an optimization.

R2 — A node key must carry the key of every upstream node it consumes. Re-deriving an upstream node's own inputs is not a substitute: upstream keys carry inputs that are not file content (see R3), so re-derivation silently drops them.

Existing links: win.workspace-tarballs carries workspaceBuildKey; win.packaged-app carries tarballsKey; win.electron-builder-dir carries packagedAppKey and resourceTreeKey; win.nsis-installer carries basePayloadKey and overlayPayloadKey; win.launcher-payload carries sourceKey.

R3 — Build outputs are never direct key inputs. hashPackageSourcePath excludes dist, .next, out, node_modules, and .od. A node that consumes another node's build output must obtain that output's identity through R2, not by hashing the output tree.

R4 — A node key must not restate a list that already exists as a constant. Derive key inputs from the constant instead. Two independent restatements of the same list drift silently and produce stale entries with no signal.

R5 — Every declared input needs a witness. See Changing a cache node.

Materialization-time parameters

Some values deliberately do not enter node keys. They are stamped onto the output every time the node is materialized, so cached content stays parameter-agnostic and is specialized on the way out.

Current materialization-time parameters:

• App version. win.packaged-app omits it. It is applied through electron-builder extraMetadata.version, then rewritten on materialization by rewriteUnpackedAppPackageVersion and rewriteWinExecutableVersion, then verified by assertMaterializedUnpackedVersionConsistency — a fail-closed check over the app package.json version, the open-design-config.json appVersion, and the Windows executable fixed file version.
• Namespace / channel and runtime endpoints. win.electron-builder-dir omits them. open-design-config.json — which carries namespace, amrProfile, telemetryRelayUrl, updateMetadataUrl, posthogKey/posthogHost, webOutputMode, and namespaceBaseRoot — is regenerated on the materialization path by writePackagedConfig.

The downstream win.nsis-payload-overlay, win.nsis-installer, win.portable-zip, and win.launcher-payload nodes carry namespace and the full packagedVersion in their keys, because their content includes the already-stamped payload. win.nsis-payload-base instead carries only versionCore: its content excludes Open Design.exe, resources/app/package.json, and resources/open-design-config.json, which are assigned to the version-bearing overlay. win.launcher-payload-base is the exception: its key carries namespace, but version identity reaches it only indirectly through the upstream sourceKey; the final win.launcher-payload archive explicitly carries the version-bearing manifest and configBody.

Requirement. A value may be a materialization-time parameter only when both hold:

1. it is re-applied unconditionally on the materialization path, so the hit and miss paths converge; and
2. the applied value is verified by a fail-closed assertion.

Adding a materialization-time parameter without (2) is not permitted.

Known asymmetry: app version satisfies (2). The other regenerated config fields — namespace, amrProfile, telemetryRelayUrl, updateMetadataUrl, posthogKey, posthogHost, webOutputMode, namespaceBaseRoot, and the packaged entrypoint fields — currently satisfy only (1): they are rewritten but not asserted.

Signing boundary

Signing material never enters cache content. resolveWinSigningCacheKey (src/win/sign.ts) contributes only the certificate SHA-1, digest algorithm, timestamp algorithm, and timestamp URL, and appears in the keys of win.nsis-payload-overlay, win.nsis-installer, and win.portable-zip.

win.nsis-payload-base correctly omits signing: it is built before ensureSignedUnpacked(), while the overlay is built after. Keep that ordering when changing the payload split.

Confidence tiers

Borrowed from specs/current/ci.md.

• certain — the key provably covers the node's full input closure, and a witness test demonstrates it (see below). Only certain nodes may participate in cross-run cache reuse policies built on top of this store.
• low confidence — anything else.

Grading is fail-closed: a node is low confidence until a witness proves otherwise. A newly added node is low confidence by default.

Declared low-confidence points

Recorded so that grading stays checkable. These are known and accepted; do not extend them.

• <platform>.workspace-build — file mode (executable bit) is not hashed by hashPackageSourcePath.
• win.launcher-payload — the seed: "nsis-base" branch takes content from the NSIS base payload but carries only the literal "nsis-base", not WIN_ARCHIVE_CACHE_VERSION. Bumping that constant without bumping the launcher payload cache versions mismatches.

Changing a cache node

1. Read this file and AGENTS.md in this directory.
2. If the change alters what build reads or writes, update the key in the same commit.
3. Bump the node's schemaVersion / cache-version constant whenever key semantics change.
4. Add or update the node's witness test in tests/. A witness proves both halves:
   • mutating each declared input changes the key;
   • mutating a known non-input (for example a package's dist tree) leaves the key unchanged.
5. Never introduce prefix or best-effort matching inside the store.