gstack/skills/design/references/RUNTIME.md

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# Optional runtime capabilities

The six Agent Skills are useful without a GStack runtime. Never install, download, build, select, update, or remove runtime capabilities merely because a skill was invoked.

Before interactive browser work, read `references/BROWSER-PROVIDERS.md` in full. It owns provider detection, consented host setup, the common readiness journey, and the explicit GStack fallback. Skill installation never proves browser readiness.

When an active specialist first reaches a capability it cannot use, name the exact capability and why it is needed. Offer to continue without it when the judgment-only or host-native path remains valid. Before any network preview, ask whether the user wants to check official setup options and exact sizes. Disclose that an uncached preview makes one public GitHub request for signed manifest metadata and sends no repository content, private URL, file, cookie, token, or credential; then STOP. A cached already-verified manifest may preview offline, but never silently fetch.

Only after the user approves that metadata check, run the non-mutating preview from this skill root: `node references/support/runtime-bootstrap.mjs preview --capability <name>` (repeat `--capability` for additional requested capabilities). It dependency-expands, reports already verified local components, exact missing components, and their summed compressed bytes. It never downloads components or mutates runtime state. Preview consent is not install consent.

User-facing setup capabilities are exactly `browser`, `design`, `diagram`, `pdf`, and `ios`. `all` means those five and intentionally excludes visible Chromium. The internal `browser-visible` capability is additive and is offered only when a workflow actually reaches a headed browser, extension, or browser-handoff step. Never offer it during ordinary headless QA.

After showing the complete preview, STOP for explicit approval. Only after approval run `node references/support/runtime-bootstrap.mjs install --capability <name> --yes`; install must reprint the identical dependency-closed plan before downloading. Signed internal components are `core`, `browser-code` (browse code and dependencies), `browser-headless` (Playwright headless shell and FFmpeg), `browser-visible` (full Chromium), `design`, `diagram`, `pdf`, and `ios`. Logical `browser` expands to `browser-code + browser-headless`; internal `browser-visible` expands to `browser-code + browser-visible` and does not require headless. Component dependencies are `browser-code → core`, `browser-headless → browser-code`, and `browser-visible → browser-code`. `diagram` depends on logical `browser`; `pdf` depends on `diagram`; `ios` is Darwin-only. Therefore a first-time headed flow previews `core + browser-code + browser-visible`, while an existing verified headless runtime downloads only missing `browser-visible`. The manifest schema is v2 with global `capabilityComponents` and `componentDependencies`, plus `targets[target].components[id]` carrying signed exact-byte artifacts.

The dependency-free Node 18+ bootstrap accepts only official GStack GitHub Release hosts, validates manifest/runtime/skill API/platform/component metadata and SHA-256, verifies a declared Cosign bundle when Cosign is available, rejects unsafe archive paths/links, and invokes the atomic managed installer. Never run `./setup` inside a standard-installed skill directory, enroll a host, or treat skill installation as runtime consent.

After doctor confirms readiness, canonical launcher bindings are `GSTACK_HOME=${GSTACK_HOME:-$HOME/.gstack}`, `GSTACK_BIN=$GSTACK_HOME/bin`, `BUN_CMD=$GSTACK_BIN/bun`, `B=$GSTACK_BIN/browse`, `D=$GSTACK_BIN/gstack-design`, and `P=$GSTACK_BIN/make-pdf`. Specialist modules may bind only the launchers they use. These assignments do not install or grant consent. Never download or install a second Bun for GStack helpers; the managed runtime owns its pinned Bun executable in the active slot.

Some retained helpers are shell scripts. `gstack doctor` verifies Bash and, on Windows, discovers Git for Windows Bash; disclose and stop at the affected helper if that prerequisite is unavailable. Python is not a global GStack prerequisite: only a specialist flow explicitly labeled as Python-dependent may request it, at the point of use and with the user's approval.

The package/runtime compatibility tuple is `schemaVersion=1`, `runtimeVersion=2.0.0`, and `skillApi=2.0`; the machine-readable copy is `references/support/runtime-contract.json`. An incompatible active runtime is unavailable, not permission to upgrade it.

Every optional-runtime tool result must satisfy `references/support/execution-result-contract.json` before it is presented as success. Success requires non-empty evidence. Empty or malformed output and explicit degraded, unsupported, or failed statuses remain non-success with stable codes; human renderings must preserve that status and code.

The developer-only fallback is `node references/support/runtime-bootstrap.mjs install --source <reviewed-checkout> --capability <name> --yes`; show its trust warning and use it only when the user explicitly selects a checkout they reviewed. If the packaged bootstrap is unavailable, stop capability setup instead of guessing a checkout-relative command. Deferring installation records no consent and must not block pure judgment.