[P2] Make scaffolding and installation guidance consume the supported host catalog; Amp is currently rejected at project creation

[ScriptedAlchemy]

User-facing failure

At main 14c9822bc6c01d8ff2788454d0e1dc7861bc3816, the framework advertises and implements the amp target, but create-agent-bundle --targets amp rejects it. A new user cannot select a supported host through the recommended entry point. This is a source-established inconsistency; this audit did not run the scaffolder or a native Amp session.

Evidence

• packages/create-agent-bundle/src/options.ts: targetNames contains only portable/claude/codex/cursor; parseTargets rejects everything else; help/prompt choices inherit this list.
• packages/create-agent-bundle/src/scaffold.ts: a second installableHostNames list and hard-coded README recovery prose know only claude/codex/cursor.
• README.md and merged feat(agent-bundle): add Amp native plugin factory #729 establish native Amp support. fix(amp): colocate standalone event workers #740/fix(test): isolate Amp installs from ambient XDG config #744 subsequently correct its runtime/test integration; this issue does not reopen those fixes.

Simplification

Use one small build-time host catalog for scaffoldable target IDs and their installation capabilities. Generate/import the tiny data needed by the scaffolder without pulling the compiler, renderer or host implementations into project creation. Update the existing tables, not a new plugin registry or service.

Keep three concepts explicit: a native compilation target, a portable-format client, and a host supported by the live-dev proxy. They are not interchangeable. This issue must not silently claim every portable client has a native adapter or that Amp supports the three existing hosts' development proxy.

Required changes

• Admit Amp in CLI validation and interactive host selection; include correct selected-host instructions in generated projects.
• Remove independently maintained target/installation lists and hard-coded recovery strings where a shared catalog can supply them.
• Keep selection explicit. Do not add Amp to every existing project's targets or change default target policy merely to fix discoverability.
• Cover all advertised native targets in scaffolder contract tests and require an explicit disposition when a target intentionally cannot use a template.
• Distinguish a portable-only project's valid client installation path from 'no plugin can be installed'; no false claim that native registration is mandatory.

Acceptance

Scaffold each template for Amp-only and a mixed selected-host set using a pinned compatible compiler/runtime pair. Check the generated configuration, README, build/validate output and actual nested Amp install root. Unknown target names still fail before writing a project. Static templates remain renderer/runtime-free. Adding another real native adapter must make an omitted scaffolder choice fail a contract test, rather than wait for a user's bug report.

Use existing isolated native-validation/fixture evidence where available; authenticated model execution is a separate proof level, not a prerequisite requiring an unavailable account.

[ScriptedAlchemy]

Closed by #759, squash-merged as b0b25d3b1338594d854da781fa22c71581f814fc.

Ask	Where it landed
Project creation consumes the supported host catalog; Amp is accepted	packages/create-agent-bundle/src/options.ts gains hostCatalog — every built-in target, whether agent-bundle install <host> accepts it, and the templates it cannot carry. targetNames includes amp, so --targets amp and the interactive prompt both offer it
One catalog, not two	scaffold.ts dropped its own ['claude', 'codex', 'cursor'] and derives installableTargets from the catalog, so a scaffolded README's install lines follow the same source
No compiler import at project creation	The catalog is a table, not a registry read: project creation still loads no adapter, renderer, or registry. tests/host-catalog.test.ts holds the table to createDefaultRegistry().names() and installHost(), and Record<TargetName, …> makes an entry mandatory at compile time, so the next adapter cannot land without a disposition
Refuse only what the compiler refuses, with a reason	amp + mcp-server is the one refused pair — Amp's skill-scoped MCP contract rejects that template's compiler-owned local status server (amp.mcp.generated-local). The prompt does not offer it; a scripted run exits 2 with Target "amp" cannot be scaffolded from the mcp-server template: … Templates for amp: minimal, or cli-tool.

Supported / unsupported, as scaffolded:

Template	amp	Evidence
minimal	supported	Packed e2e scaffolds --targets portable,amp, installs the packed tarballs, runs the project's check, and asserts the emitted artifact/.amp/plugins/minimal-project/skills/getting-started/SKILL.md
cli-tool	supported	agent-bundle validate --target amp clean on the template; AB4765 warns only that Amp emits no routed CLI of its own
mcp-server	refused at project creation	agent-bundle validate --target amp over the template reports amp.mcp.generated-local; refusing at creation replaces a first-build failure

Two corrections rode along in files the change already touched: the mcp-server template summary
said "one conventional src/mcp/<id>.ts entry" (the template ships
src/mcp/status/tools/report-status.tsx with route-unit and projection pools), and scaffolded
READMEs now invoke npx --no-install agent-bundle, since agent-bundle is always a local
dependency there and a bare npx can only mean an accidental registry fetch.

Docs updated in both locales — guide/start/quick-start, guide/start/capabilities, and the
guide/development/troubleshooting row for a target rejected at project creation — plus
packages/create-agent-bundle/README.md. Changeset: patch on create-agent-bundle.

Gate on a branch containing current main: pnpm build, pnpm typecheck, pnpm lint,
pnpm test:unit (4486 tests, 0 failures), pnpm docs:site:build, pnpm test:packed (15 files,
44 tests), and the packed scaffolder e2e re-run after the rebase (4/4). Also exercised by hand
through the built CLI: the refused pair exits 2 with the message above, and
--template minimal --targets amp writes targets: ['amp'].