feat(provider): add native Google Gemini API adapter (Phase 4)

Adds internal/provider/google, the second native cloud adapter (following
internal/provider/anthropic's pattern) on top of Phase 1's provider-neutral
tool-use loop, wired to a Docker-sandboxed NativeRunner under agent.type:
"google" -- a separate execution path and budget bucket from the existing
CLI-subprocess "gemini" ContainerRunner, which is untouched.

Wire-format research (the highest-risk part of this adapter): Gemini's
multi-turn function-calling shape was resolved by cross-referencing the
REST API reference's own generateContent example against the go-genai SDK's
struct tags on GitHub -- both agree on functionCall/functionResponse parts
keyed by "name" (with an optional "id" for round-tripping ToolCall.ID),
with the response fed back inside a "user"-role Content (Gemini has no
tool/function role, mirroring Anthropic's lack of one). A separate fetched
source (the function-calling guide page) was deliberately discarded as a
reference for this shape -- it documents a different, newer "Interactions
API" whose call_id/type:"function_result" structure doesn't fit the
contents/parts/candidates shape used everywhere else.

- internal/provider/google: request/response translation, systemInstruction
  handling, role mapping (assistant->model, tool-results->user role),
  per-model-prefix pricing table (2.5 Pro/Flash/Flash-Lite, 2.0, 1.5 tiers)
- internal/retry: IsRateLimitError additively extended for RESOURCE_EXHAUSTED
- internal/config: RunnersConfig.Google/GoogleEnabled()
- internal/cli/serve.go, run.go: runners["google"] construction mirroring
  the Anthropic wiring exactly (Docker sandbox default)
- docs/api-keys-setup.md: Google marked wired-up, budget-bucket/disable/
  verify guidance added matching the Anthropic section

go build/vet/test -race all pass. No live Gemini API key available in this
environment; verified via fake-httptest-server adapter tests (plain text,
tool-use round-trip, multi-turn tool-result, rate-limit error matching) plus
a Pool/NativeRunner routing test. Live E2E is a follow-up once a key is
configured, same as Phase 2's Anthropic adapter.

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

1 files changed, 21 insertions, 0 deletions

diff --git a/internal/cli/serve.go b/internal/cli/serve.go
index 8b6cc6a..57c2cbd 100644
--- a/internal/cli/serve.go
+++ b/internal/cli/serve.go
@@ -17,6 +17,7 @@ import (
 	"github.com/thepeterstone/claudomator/internal/executor"
 	"github.com/thepeterstone/claudomator/internal/notify"
 	"github.com/thepeterstone/claudomator/internal/provider/anthropic"
+	"github.com/thepeterstone/claudomator/internal/provider/google"
 	"github.com/thepeterstone/claudomator/internal/provider/openaicompat"
 	"github.com/thepeterstone/claudomator/internal/storage"
 	"github.com/thepeterstone/claudomator/internal/version"
@@ -174,6 +175,26 @@ func serve(addr, basePath string) error {
 		logger.Info("anthropic runner registered", "default_model", pc.DefaultModel, "sandbox", "docker")
 	}
 
+	if pc, ok := cfg.Providers["google"]; ok && pc.APIKey != "" && cfg.Runners.GoogleEnabled() {
+		timeout := time.Duration(0)
+		if pc.TimeoutSeconds > 0 {
+			timeout = time.Duration(pc.TimeoutSeconds) * time.Second
+		}
+		runners["google"] = &executor.NativeRunner{
+			Provider:     google.New(pc.APIKey, pc.Endpoint, timeout),
+			Logger:       logger,
+			LogDir:       cfg.LogDir,
+			DefaultModel: pc.DefaultModel,
+			// Native cloud providers get real container isolation
+			// (sandbox.DockerSandbox) rather than HostSandbox's host-side
+			// path-prefix confinement — same reasoning as the "anthropic"
+			// runner above.
+			SandboxKind:  "docker",
+			SandboxImage: cfg.SandboxImage,
+		}
+		logger.Info("google runner registered", "default_model", pc.DefaultModel, "sandbox", "docker")
+	}
+
 	pool := executor.NewPool(cfg.MaxConcurrent, runners, store, logger)
 	pool.Classifier = &executor.Classifier{
 		LLM:              localClient,