phase 4: chatd — multi-provider LLM dispatcher (ollama / cloud / openrouter / opencode / kimi)

new cmd/chatd on :3220 routes /v1/chat to the right provider based
on model-name prefix or :cloud suffix. closes the architectural gap
named in lakehouse.toml [models]: tiers map to model IDs, but until
phase 4 there was no service that could actually CALL those models
from go.

routing rules (registry.Resolve):
  ollama/<m>          → local Ollama (prefix stripped)
  ollama_cloud/<m>    → Ollama Cloud
  <m>:cloud           → Ollama Cloud (suffix variant — kimi-k2.6:cloud)
  openrouter/<v>/<m>  → OpenRouter (prefix stripped, OpenAI-compat)
  opencode/<m>        → OpenCode unified Zen+Go
  kimi/<m>            → Kimi For Coding (api.kimi.com/coding/v1)
  bare names          → local Ollama (default)

provider implementations:
- internal/chat/types.go      Provider interface, Request/Response, errors
- internal/chat/registry.go   prefix + :cloud suffix dispatch
- internal/chat/ollama.go     local Ollama via /api/chat (think=false default)
- internal/chat/ollama_cloud.go  Ollama Cloud via /api/generate (Bearer auth)
- internal/chat/openai_compat.go shared OpenAI Chat Completions for the
                                 OpenRouter/OpenCode/Kimi family
- internal/chat/builder.go    BuildRegistry from BuilderInput;
                              ResolveKey reads env then .env file fallback

config:
- ChatdConfig in internal/shared/config.go with bind, ollama_url,
  per-provider key env names + .env fallback paths, timeout
- Gateway gains chatd_url + /v1/chat + /v1/chat/* routes
- lakehouse.toml [chatd] block with /etc/lakehouse/<provider>.env defaults

tests (19 in internal/chat):
- registry: prefix + :cloud + errors + telemetry + provider listing
- ollama: happy path + prefix strip + format=json + 500 mapping +
  flatten_messages
- openai_compat: happy path + format=json + 429 mapping + zero-choices

think=false default in ollama + ollama_cloud — local hot path skips
reasoning, low-budget callers (the playbook_lift judge at max_tokens=10)
get direct answers instead of empty content + done_reason=length.
proven via chatd_smoke acceptance.

acceptance gate: scripts/chatd_smoke.sh — 6/6 PASS:
1. /v1/chat/providers lists exactly registered providers (1 in dev mode)
2. bare model → ollama default with content + token counts + latency
3. explicit ollama/<m> → prefix stripped at upstream
4. <m>:cloud without ollama_cloud registered → 404 (no silent fall-through)
5. unknown/<m> → falls through to default → upstream 502 (no prefix rewrite)
6. missing model field → 400

just verify: PASS (vet + 30 packages × short tests + 9 smokes).
chatd_smoke is a domain smoke (not in just verify, mirrors matrix /
observer / pathway pattern).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

cmd/gateway/main.go

@@ -47,6 +47,7 @@ func main() {
 		"pathwayd_url": cfg.Gateway.PathwaydURL,
 		"matrixd_url":  cfg.Gateway.MatrixdURL,
 		"observerd_url": cfg.Gateway.ObserverdURL,
+		"chatd_url":    cfg.Gateway.ChatdURL,
 	}
 	for k, v := range upstreams {
 		if v == "" {
@@ -69,6 +70,7 @@ func main() {
 	pathwaydURL := mustParseUpstream("pathwayd_url", cfg.Gateway.PathwaydURL)
 	matrixdURL := mustParseUpstream("matrixd_url", cfg.Gateway.MatrixdURL)
 	observerdURL := mustParseUpstream("observerd_url", cfg.Gateway.ObserverdURL)
+	chatdURL := mustParseUpstream("chatd_url", cfg.Gateway.ChatdURL)
 
 	storagedProxy := gateway.NewProxyHandler(storagedURL)
 	catalogdProxy := gateway.NewProxyHandler(catalogdURL)
@@ -79,6 +81,7 @@ func main() {
 	pathwaydProxy := gateway.NewProxyHandler(pathwaydURL)
 	matrixdProxy := gateway.NewProxyHandler(matrixdURL)
 	observerdProxy := gateway.NewProxyHandler(observerdURL)
+	chatdProxy := gateway.NewProxyHandler(chatdURL)
 
 	if err := shared.Run("gateway", cfg.Gateway.Bind, func(r chi.Router) {
 
@@ -103,6 +106,9 @@ func main() {
 		r.Handle("/v1/matrix/*", matrixdProxy)
 		// Observer — /v1/observer/*  (autonomous-iteration witness loop)
 		r.Handle("/v1/observer/*", observerdProxy)
+		// Chat — /v1/chat (LLM dispatcher) + /v1/chat/providers
+		r.Handle("/v1/chat", chatdProxy)
+		r.Handle("/v1/chat/*", chatdProxy)
 	}, cfg.Auth); err != nil {
 		slog.Error("server", "err", err)
 		os.Exit(1)