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>

llm/message.go

@@ -0,0 +1,71 @@
+package llm
+
+import "strings"
+
+// Role identifies the author of a message.
+type Role string
+
+const (
+	RoleSystem    Role = "system"
+	RoleUser      Role = "user"
+	RoleAssistant Role = "assistant"
+	RoleTool      Role = "tool"
+)
+
+// Message is one turn in a conversation.
+//
+// Exactly which fields are populated depends on the role: user and system
+// messages carry Parts; assistant messages carry Parts and/or ToolCalls;
+// tool messages carry ToolResults. Providers translate this canonical shape
+// to and from their wire formats.
+type Message struct {
+	Role Role
+
+	// Parts is the message content (text, images, ...).
+	Parts []Part
+
+	// ToolCalls are tool invocations requested by the assistant
+	// (meaningful only when Role == RoleAssistant).
+	ToolCalls []ToolCall
+
+	// ToolResults carry the outcomes of earlier ToolCalls
+	// (meaningful only when Role == RoleTool).
+	ToolResults []ToolResult
+}
+
+// Text returns the concatenation of all text parts in the message.
+func (m Message) Text() string {
+	var b strings.Builder
+	for _, p := range m.Parts {
+		if t, ok := p.(TextPart); ok {
+			b.WriteString(t.Text)
+		}
+	}
+	return b.String()
+}
+
+// SystemText constructs a system message with one text part.
+func SystemText(s string) Message {
+	return Message{Role: RoleSystem, Parts: []Part{Text(s)}}
+}
+
+// UserText constructs a user message with one text part.
+func UserText(s string) Message {
+	return Message{Role: RoleUser, Parts: []Part{Text(s)}}
+}
+
+// UserParts constructs a user message from arbitrary content parts
+// (e.g. text plus images).
+func UserParts(parts ...Part) Message {
+	return Message{Role: RoleUser, Parts: parts}
+}
+
+// AssistantText constructs an assistant message with one text part.
+func AssistantText(s string) Message {
+	return Message{Role: RoleAssistant, Parts: []Part{Text(s)}}
+}
+
+// ToolResultsMessage constructs a tool message carrying one or more results.
+func ToolResultsMessage(results ...ToolResult) Message {
+	return Message{Role: RoleTool, ToolResults: results}
+}