agent-loop: new crate — LLM loop kernel + Model clients (phase 0)

Extract the LLM agent loop into a standalone workspace crate with zero
deps on skald-core/core-api (blueprint project-loop.md, D13-D15):

- kernel: round loop, model fallback with rebuild, parallel tool fan-out
  (ordered id alloc / bounded concurrent exec / ordered record), streaming
  deltas drained before outcomes, sticky cancellation
- models: OpenAiModel/AnthropicModel/OllamaModel/LmStudioModel ported from
  llm-client onto the Model trait; ModelError carries the HTTP status;
  is_retriable default = the 401/403/404/422 rule
- DTL as crate protocol (ToolRendering Inline/DeferredToolReference/
  SystemToolBlock; Anthropic conversions + Kimi system+tools passthrough),
  host catalog behind ActivationSource/ToolActivator
- HistoryStore durability contract + InMemoryStore; LinearAssembler with
  well-formed projection (incl. DTL injection, summary, crash survivors)
- LoopManager singleton (broadcast bus + live registry), one live loop
  per conversation, orphan-marking on start_turn
- 32 tests green (kernel §13 suite, assembler DTL, SSE/Anthropic ports),
  clippy clean

crates/agent-loop/src/ids.rs

@@ -0,0 +1,54 @@
+//! Opaque id newtypes. The store contract requires `MessageId` and `ToolCallId`
+//! to be **monotonically increasing per frame**: a concurrent fan-out allocates
+//! ids in call order BEFORE execution, and the model reconstructs results by id.
+
+use std::fmt;
+
+/// Identifies a conversation (Skald: `"session:42"`; InMemory: any string).
+#[derive(Debug, Clone, PartialEq, Eq, Hash, PartialOrd, Ord)]
+pub struct ConversationId(pub String);
+
+impl ConversationId {
+    pub fn new(s: impl Into<String>) -> Self { Self(s.into()) }
+    pub fn as_str(&self) -> &str { &self.0 }
+}
+
+impl fmt::Display for ConversationId {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { f.write_str(&self.0) }
+}
+
+impl From<&str> for ConversationId {
+    fn from(s: &str) -> Self { Self(s.to_string()) }
+}
+impl From<String> for ConversationId {
+    fn from(s: String) -> Self { Self(s) }
+}
+
+macro_rules! int_id {
+    ($name:ident, $doc:literal) => {
+        #[doc = $doc]
+        #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, PartialOrd, Ord)]
+        pub struct $name(pub i64);
+
+        impl $name {
+            pub fn get(self) -> i64 { self.0 }
+        }
+
+        impl fmt::Display for $name {
+            fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { write!(f, "{}", self.0) }
+        }
+
+        impl From<i64> for $name {
+            fn from(v: i64) -> Self { Self(v) }
+        }
+    };
+}
+
+int_id!(FrameId, "A conversation frame (root frame = the conversation; children = sub-agents).");
+int_id!(MessageId, "A stored message. Monotonically increasing per frame.");
+int_id!(ToolCallId, "A stored tool call. Monotonically increasing per frame.");
+int_id!(TaskId, "An async delegated task.");
+int_id!(SummaryId, "A compaction summary.");
+
+/// Key of a model inside a `ModelSelector` ("kimi-k3", "claude-sonnet-4", …).
+pub type ModelId = String;