feat: foundations — canonical types, Parse grammar, env DSNs, health, chains

Phase 1 of the majordomo build:
- llm/ canonical contract (messages, parts, tools, capabilities, streaming,
  Model/Provider, error classification)
- health/ clock-injected tracker (threshold bench, exponential capped
  cooldown, reset-on-success)
- root Registry + Parse (verbatim model ids, inline recursive alias
  expansion with cycle detection, chain dedup), LLM_* env-DSN providers
  (go-llm parity: lazy fallback + eager LoadEnv), health-aware chain
  executor behind the Model interface
- provider/fake scriptable test provider; hermetic test suite incl. the
  trailing-thinking chain and foreman:// env loading
- ADRs 0001-0008, CLAUDE.md, README (honest matrix), CI workflow,
  docs/phase-1-design.md

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

docs/adr/0002-canonical-message-model.md

@@ -0,0 +1,53 @@
+# ADR-0002: Canonical message/content model
+
+**Status:** Accepted — 2026-06-10
+
+## Context
+
+Every provider has a different wire shape for conversations, content,
+tool calls, and system prompts. majordomo needs one canonical shape that all
+providers translate to/from, expressive enough for multimodality and tool
+loops, small enough to keep providers honest.
+
+## Decision
+
+- `Message{Role, Parts, ToolCalls, ToolResults}` with roles system / user /
+  assistant / tool. `Part` is a **sealed** interface (`TextPart`,
+  `ImagePart`) so providers can switch exhaustively; new media kinds are
+  deliberate API changes, not silent pass-throughs.
+- `ImagePart` is **bytes + MIME only** — no URL form. The media pipeline
+  must inspect/resize/transcode images against target capabilities, which
+  requires bytes; fetching remote URLs is the caller's job, not a hidden
+  network dependency inside a model call.
+- `Request.System` is a dedicated top-level field (maps to Anthropic
+  `system`, Google `SystemInstruction`, an OpenAI/Ollama system message).
+  RoleSystem messages in the history are also accepted and folded by
+  providers. Request also carries Tools, ToolChoice, Schema/SchemaName, and
+  sampling knobs; per-call mutation happens via `Option` funcs applied to a
+  copy, so Request values are reusable.
+- Model ids never carry behavior suffixes: unlike go-llm there is **no
+  `:low/:medium/:high` reasoning-suffix grammar** (it conflicts with
+  verbatim model ids like `minimax-m3:cloud`, see ADR-0003). Reasoning
+  effort will be a request option when providers land.
+- `Response{Parts, ToolCalls, FinishReason, Usage, Model, Raw}` — `Model`
+  names the target that actually served the request (vital with chains);
+  `Raw` is the provider-native escape hatch, never required.
+- Streaming (`Stream.Next() → StreamEvent`): text deltas stream as they
+  arrive; **tool-call arguments are buffered until complete** (consumers
+  never see partial JSON); the final event carries the accumulated
+  `*Response`; `io.EOF` terminates.
+
+## Consequences
+
+- Providers stay translation layers; nothing provider-specific leaks into
+  the canonical API.
+- Callers needing remote images fetch them first — explicit, testable.
+- Partial-tool-call streaming UIs are out of scope (acceptable: arguments
+  are rarely useful before they parse).
+
+## Alternatives considered
+
+- Open `Part` interface — silent content drops on unknown kinds. Rejected.
+- URL image parts with lazy fetch — hidden I/O inside Generate, breaks
+  capability normalization. Rejected.
+- go-llm-style reasoning suffixes — see ADR-0003. Rejected.