feat(executor): wire the agent MCP back-channel for gemini containers (Phase 4)

ContainerRunner previously skipped the MCP back-channel for gemini agents, so
they ran tool-less. It now mints a per-task token for gemini too and registers
the agent MCP server in the gemini CLI's user settings
(agentHome/.gemini/settings.json → $HOME/.gemini in-container) using the
gemini-cli mcpServers/httpUrl schema with a bearer header. With MCP enabled,
gemini also receives the planning preamble that points at the ask_user/
report_summary/spawn_subtask/record_progress tools.

Config generation is unit-tested (TestWriteGeminiMCPSettings) and the write is
in the run setup path. CAVEAT: whether the gemini CLI actually invokes these
tools in non-interactive (-p) mode — and how it handles tool auto-approval —
is NOT verified against a live gemini binary in this environment; this lands
the plumbing for a follow-up spike. No regression risk for gemini runs: a
config issue degrades to the prior tool-less behavior.

https://claude.ai/code/session_01SESwn7kQ7oP62trWw6pc39

1 files changed, 30 insertions, 0 deletions

diff --git a/internal/executor/container_test.go b/internal/executor/container_test.go
index 3d0887c..521e1cb 100644
--- a/internal/executor/container_test.go
+++ b/internal/executor/container_test.go
@@ -107,6 +107,36 @@ func TestWriteMCPConfig(t *testing.T) {
 	}
 }
 
+func TestWriteGeminiMCPSettings(t *testing.T) {
+	agentHome := t.TempDir()
+	if err := writeGeminiMCPSettings(agentHome, "http://host.docker.internal:8484/mcp", "tok-xyz"); err != nil {
+		t.Fatalf("writeGeminiMCPSettings: %v", err)
+	}
+	data, err := os.ReadFile(filepath.Join(agentHome, ".gemini", "settings.json"))
+	if err != nil {
+		t.Fatalf("read settings: %v", err)
+	}
+	var parsed struct {
+		MCPServers map[string]struct {
+			HTTPURL string            `json:"httpUrl"`
+			Headers map[string]string `json:"headers"`
+		} `json:"mcpServers"`
+	}
+	if err := json.Unmarshal(data, &parsed); err != nil {
+		t.Fatalf("settings is not valid JSON: %v", err)
+	}
+	srv, ok := parsed.MCPServers["claudomator"]
+	if !ok {
+		t.Fatal("expected claudomator server entry")
+	}
+	if srv.HTTPURL != "http://host.docker.internal:8484/mcp" {
+		t.Errorf("unexpected httpUrl: %q", srv.HTTPURL)
+	}
+	if srv.Headers["Authorization"] != "Bearer tok-xyz" {
+		t.Errorf("expected bearer header, got %q", srv.Headers["Authorization"])
+	}
+}
+
 func TestContainerRunner_BuildInnerCmd(t *testing.T) {
 	runner := &ContainerRunner{}