fix(serve): install bundle modules on cold start; declare all 4 providers

[manojp99]

Summary

Two coupled changes that close the "fresh install → serve chat-completions fails because providers aren't installed" gap:

1. bundle.md now declares all 4 default providers so cold-prep installs all of them.
2. serve chat-completions lifespan triggers the same install-on-first-use path that run already uses.

Evidence the gap exists

Confirmed in a DTU smoke test on a fresh Ubuntu container:

# Fresh `uv tool install amplifier-agent`
amplifier-agent run -y "say hi"
  → succeeds; venv now has _editable_impl_amplifier_module_provider_anthropic.pth + 9 others

# Same fresh install
amplifier-agent serve chat-completions --config <providers-block>
  → ProviderModuleNotInstalledError: provider 'anthropic': module 'anthropic' not installed
  → venv has ZERO amplifier_module_* packages

The install machinery works correctly; serve just doesn't trigger it.

Investigation findings

The install trigger is prepared.resolver.async_resolve(module_id, source_hint) in amplifier_foundation.bundle._prepared.BundleModuleResolver. It installs via ModuleActivator.activate() (→ uv pip install --editable).

How run reaches it:
_execute_turn → inject_provider → Engine.boot(bundle_override=prepared) → prepared.create_session() → session.initialize() → kernel calls resolver.async_resolve("provider-anthropic", source) → package installed.

Why serve misses it:
The lifespan never calls create_session() (that's per-request in _session_runner.run_chat_turn). list_provider_models() tries importlib.import_module("amplifier_module_provider_anthropic") before any session is created — and fails with ProviderModuleNotInstalledError.

Why cold-prep doesn't help alone:
bundle.prepare(install_deps=True) processes session.orchestrator, session.context, and top-level providers:/tools:/hooks: — but NOT session.provider:. The comment in bundle.md claiming "declaring it here ensures the cold-prepare step installs the provider module" was wrong.

Idempotency: async_resolve has a fast path (if module_id in self._paths) that returns immediately on warm cache. ModuleActivator skips reinstall when already present.

Why this is the right fix

A previous discussion considered a wrapper-side bootstrap (have amplifier-app-opencode run amplifier-agent run once before spawning the server). That's wrapper-specific — every consumer of amplifier-agent serve (Slack bots, web UIs, custom integrations) would have to reimplement the same bootstrap.

Fixing it in amplifier-agent itself makes the install-on-cold-start behavior universal.

File changes

File	Change
src/amplifier_agent_lib/bundle/bundle.md	Add top-level providers: section with all 4 CATALOG providers as install-only stubs (module + source, no credentials). Update session.provider comment to reflect actual mechanics.
src/amplifier_agent_http/app.py	Import PROVIDER_CATALOG. Call prepared.resolver.async_resolve(module_id, source) for every CATALOG entry in lifespan before the providers loop. Failures are logged as warnings; the providers loop then reports them as structured errors.
src/amplifier_agent_cli/modes/single_turn.py	Clear prepared.mount_plan["providers"] = [] before inject_provider. Now that bundle.md populates top-level providers: with 4 stubs, inject_provider's "no-op if already present" guard would skip injecting the runtime provider. Mirrors the pattern _session_runner.run_chat_turn already uses.
tests/http/test_lifespan_module_install.py	New: 3 tests verifying the wire-up (trigger called, failure is non-fatal → exit 2, idempotent on warm cache).
CHANGELOG.md	Add to [Unreleased] Added / Changed.

Compatibility

• Single-turn mode (amplifier-agent run) is unchanged in behavior — same code path, same runtime result.
• host_config.providers schema (from feat(http)!: require host_config.providers; fail loudly on misconfig #69) is unchanged.
• Wire protocol unchanged.
• No new environment variables.

Backlog impact

Resolves the install gap surfaced by the DTU smoke test. Server mode now works from a fresh uv tool install with zero manual prep steps.

Companion update

amplifier-app-opencode users no longer need to know about bundle prep or post-install hooks — amplifier-opencode launch just works after a fresh install.