Tighten AGENTS.md and extract LLM provider checklist to skill

- Tighten all sections (279 -> 159 lines) without dropping rules.
- Reorganize: git rules moved next to issues/PRs.
- Defer contributor gate details to CONTRIBUTING.md.
- Replace stale npx tsx test command with node (strip-only mode); add ./test.sh + e2e warning.
- Releasing: explicit WebAuthn briefing step, no bash timeout, stop on partial publish failure.
- Move LLM provider checklist to .pi/skills/add-llm-provider.md.

.pi/skills/add-llm-provider.md

@@ -0,0 +1,57 @@
+---
+name: add-llm-provider
+description: Checklist for adding a new LLM provider to packages/ai. Covers core types, provider implementation, lazy registration, model generation, the full test matrix, coding-agent wiring, and docs.
+---
+
+# Adding a New LLM Provider (packages/ai)
+
+A new provider touches multiple files. Work through these steps in order.
+
+## 1. Core Types (`packages/ai/src/types.ts`)
+
+- Add API identifier to `Api` type union (e.g. `"bedrock-converse-stream"`).
+- Create options interface extending `StreamOptions`.
+- Add mapping to `ApiOptionsMap`.
+- Add provider name to `KnownProvider` type union.
+
+## 2. Provider Implementation (`packages/ai/src/providers/`)
+
+Create a provider file exporting:
+
+- `stream<Provider>()` returning `AssistantMessageEventStream`.
+- `streamSimple<Provider>()` for `SimpleStreamOptions` mapping.
+- Provider-specific options interface.
+- Message/tool conversion functions.
+- Response parsing that emits standardized events (`text`, `tool_call`, `thinking`, `usage`, `stop`).
+
+## 3. Provider Exports and Lazy Registration
+
+- Add a package subpath export in `packages/ai/package.json` pointing at `./dist/providers/<provider>.js`.
+- Add `export type` re-exports in `packages/ai/src/index.ts` for provider option types that should remain available from the root entry.
+- Register the provider in `packages/ai/src/providers/register-builtins.ts` via lazy loader wrappers; do not statically import provider implementation modules there.
+- Add credential detection in `packages/ai/src/env-api-keys.ts`.
+
+## 4. Model Generation (`packages/ai/scripts/generate-models.ts`)
+
+- Add logic to fetch/parse models from the provider source.
+- Map to the standardized `Model` interface.
+
+## 5. Tests (`packages/ai/test/`)
+
+- Always add the provider to `stream.test.ts` with at least one representative model, even if it reuses an existing API impl such as `openai-completions`.
+- Add the provider to the broader matrix where applicable: `tokens.test.ts`, `abort.test.ts`, `empty.test.ts`, `context-overflow.test.ts`, `unicode-surrogate.test.ts`, `tool-call-without-result.test.ts`, `image-tool-result.test.ts`, `total-tokens.test.ts`, `cross-provider-handoff.test.ts`.
+- For `cross-provider-handoff.test.ts`, add at least one provider/model pair. If the provider exposes multiple model families (e.g. GPT and Claude), add at least one pair per family.
+- For non-standard auth, create a utility (e.g. `bedrock-utils.ts`) with credential detection.
+
+## 6. Coding Agent (`packages/coding-agent/`)
+
+- `src/core/model-resolver.ts`: add default model ID to `defaultModelPerProvider`.
+- `src/core/provider-display-names.ts`: add API-key login display name so `/login` and related UI show the provider for built-in API-key auth.
+- `src/cli/args.ts`: add env var documentation.
+- `README.md`: add provider setup instructions.
+- `docs/providers.md`: add setup instructions, env var, and `auth.json` key.
+
+## 7. Documentation
+
+- `packages/ai/README.md`: add to providers table, document options/auth, add env vars.
+- `packages/ai/CHANGELOG.md`: add entry under `## [Unreleased]`.