feat(#2002): self-healing runtime build for plugin-marketplace installs (#2036)

The compiled gsd-core/bin/lib/*.cjs modules are gitignored build artifacts
(ADR-457) shipped prebuilt in the npm tarball. A Claude Code plugin-marketplace
/ git-clone install materializes the repo tree directly and never runs
`npm run build:lib`, so those ~148 files are absent and every CLI command dies
at load with `Cannot find module './lib/cli-exit.cjs'`.

gsd-tools.cjs now calls ensureRuntimeBuild() before its ./lib requires: a new
committed bin helper that compiles the tree once on demand (lock-guarded,
incremental-cache-cleared, portable `node <tsc>` invocation) when the sentinel
cli-exit.cjs is missing, and surfaces an actionable error when TypeScript is
unavailable. The already-built npm path is a single fs.existsSync no-op.
ADR-457 (gitignored, build-at-publish) is preserved; no release-pipeline change.

Verified against a simulated marketplace checkout (148 build outputs removed):
the CLI self-heals and the result is byte-identical to `npm run build:lib`.

Closes #2002

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

docs/how-to/install-on-your-runtime.md

@@ -102,6 +102,8 @@ The `gsd-tools` binary (installed as part of the `@opengsd/gsd-core` npm package
 
 Node.js (`node`) must also be available on your `PATH`. The plugin's always-on guard hooks (wired in `hooks/hooks.json`) are invoked as `node "${CLAUDE_PLUGIN_ROOT}/hooks/<script>"`. Some Claude Code distributions ship as a standalone binary and do not expose a `node` executable on `PATH`; in those environments the plugin's hooks will not run. Verify with `node --version` before relying on the plugin hooks.
 
+**Runtime build (self-healing).** The runtime CLI's compiled modules under `gsd-core/bin/lib/*.cjs` are build artifacts (ADR-457): they are compiled from `src/*.cts` by `npm run build:lib` and shipped prebuilt in the npm tarball. A plugin-marketplace or git-clone install materializes the repository tree directly and never runs that build step, so those files are initially absent. The CLI heals this automatically: the first `gsd-tools` invocation detects the missing output and compiles it once (using the bundled `typescript` devDependency), then proceeds normally. You may see a one-time `gsd: runtime library not built — compiling once…` notice on stderr; subsequent commands are unaffected. If auto-build cannot run (for example `node_modules` was pruned to production-only and `typescript` is unavailable), the CLI prints an actionable message telling you to run `npm install && npm run build:lib` in the plugin directory.
+
 #### Claude plugin marketplace discovery (ZCODE and compatible runtimes)
 
 GSD Core also ships a `.claude-plugin/marketplace.json` marketplace manifest (sibling to `plugin.json`). Runtimes that implement the Claude plugin marketplace contract — such as ZCODE — can discover and install GSD Core from a custom marketplace source without a manual clone: