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/models/mod.rs

@@ -0,0 +1,42 @@
+//! Shipped `Model` clients (blueprint D13): OpenAI-compatible, Anthropic,
+//! Ollama, LM Studio — plus the shared SSE decoder and HTTP helpers.
+//!
+//! All clients are stateless (connection config only) and share the same
+//! failure policy: if a stream dies BEFORE any delta, the client retries
+//! buffered on the same model (providers rejecting `stream` keep working); a
+//! mid-stream failure propagates to the caller's fallback logic.
+
+pub mod anthropic;
+pub mod lm_studio;
+pub mod ollama;
+pub mod openai;
+mod sse;
+
+pub use anthropic::AnthropicModel;
+pub use lm_studio::LmStudioModel;
+pub use ollama::OllamaModel;
+pub use openai::OpenAiModel;
+pub(crate) use sse::SseDecoder;
+
+use serde_json::Value;
+
+/// Converts a reqwest `HeaderMap` into a JSON object (for payload logging).
+pub(crate) fn headers_to_json(headers: &reqwest::header::HeaderMap) -> Value {
+    let map: serde_json::Map<String, Value> = headers
+        .iter()
+        .map(|(k, v)| (k.as_str().to_string(), v.to_str().unwrap_or("<binary>").into()))
+        .collect();
+    Value::Object(map)
+}
+
+/// Raw error body → JSON for the payload log: parsed JSON when the provider
+/// returned JSON, else the raw text wrapped as a JSON string so a non-JSON
+/// body (HTML gateway page) is still preserved verbatim.
+pub(crate) fn error_response_body(text: String) -> Value {
+    serde_json::from_str::<Value>(&text).unwrap_or(Value::String(text))
+}
+
+/// Redacted preview of an API key: first 7 chars + "***".
+pub(crate) fn redact_key(key: &str) -> String {
+    if key.len() > 7 { format!("{}***", &key[..7]) } else { "***".to_string() }
+}