refactor(executor): extract provider-neutral tool-use loop (Phase 1)

Splits LocalRunner's OpenAI-specific agentic loop into reusable, provider-
agnostic pieces so later phases can add native Anthropic/OpenAI/Google/Groq/
OpenRouter adapters without duplicating the control flow:

- internal/provider: neutral Provider/ChatRequest/ChatResponse types, plus
  an openaicompat adapter wrapping the existing internal/llm.Client unchanged
- internal/sandbox: Sandbox interface + HostSandbox (git clone/push/cleanup,
  read_file/write_file/run_bash/glob), lifted verbatim from local.go/localtools.go
- internal/agentloop: the extracted tool-use loop (request/response/tool-
  dispatch/loop, ask_user blocking, stream-json envelope, summary fallback)
- internal/agentchannel: AgentChannel/SubtaskSpec/BlockedError/ErrAgentBlocked
  moved out of internal/executor so agentloop can use them without an import
  cycle; internal/executor re-exports via type aliases, so no call site changes
- internal/executor/nativerunner.go: NativeRunner replaces LocalRunner,
  wiring agentloop.Loop + openaicompat + HostSandbox together
- config.Providers map[string]ProviderConfig added (unused until Phase 2+)

Zero intended behavior change: go test -race ./... passes across all
packages, and end-to-end stream-json/summary/changestats output was verified
byte-compatible against a fake OpenAI-compatible server. Adds test coverage
for sandbox tool-dispatch (git clone/push, read/write/bash/glob) that
LocalRunner never had.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01V1moSNCJRcP6kykA4tyUSs

1 files changed, 17 insertions, 0 deletions

diff --git a/internal/config/config.go b/internal/config/config.go
index 80777ff..640e933 100644
--- a/internal/config/config.go
+++ b/internal/config/config.go
@@ -63,6 +63,20 @@ func (r RunnersConfig) GeminiEnabled() bool    { return r.Gemini == nil || *r.Ge
 func (r RunnersConfig) LocalEnabled() bool     { return r.Local == nil || *r.Local }
 func (r RunnersConfig) ContainerEnabled() bool { return r.Container == nil || *r.Container }
 
+// ProviderConfig configures a native (or OpenAI-compatible) LLM provider
+// backend for the multi-provider harness — see docs/api-keys-setup.md. Phase
+// 1 only adds this type so config has somewhere for it to land; it is not yet
+// read by runner construction (no native provider adapters exist yet besides
+// the openaicompat one LocalModel already configures). Keyed by provider name
+// in the [providers.<name>] TOML table, e.g. [providers.groq],
+// [providers.anthropic].
+type ProviderConfig struct {
+	Endpoint       string `toml:"endpoint"`
+	APIKey         string `toml:"api_key"`
+	DefaultModel   string `toml:"default_model"`
+	TimeoutSeconds int    `toml:"timeout_seconds"`
+}
+
 type Config struct {
 	DataDir          string        `toml:"data_dir"`
 	DBPath           string        `toml:"-"`
@@ -89,6 +103,9 @@ type Config struct {
 	LocalModel       LocalModel    `toml:"local_model"`
 	Runners          RunnersConfig `toml:"runners"`
 	Budget           BudgetConfig  `toml:"budget"`
+	// Providers configures native/OpenAI-compatible LLM backends by name (see
+	// ProviderConfig). Unused by runner construction in Phase 1.
+	Providers map[string]ProviderConfig `toml:"providers"`
 	// ExternalBindAllowed must be explicitly true to bind a non-loopback address.
 	ExternalBindAllowed bool `toml:"external_bind_allowed"`
 }