feat(capabilityclient): add PrintAIInfo and forward CTX_AI_MODEL in Generate

  PrintAIInfo(w) reads CTX_AI_PROVIDER and CTX_AI_MODEL from the container
  environment and writes "ctx: using <provider> (<model>)" to w before AI
  work begins, giving users consistent visibility into which provider and
  model is active.

  Generate() now includes model in the ai.generate POST body when
  CTX_AI_MODEL is set, enabling the host capability server to route
  the call to a per-call model override.

Author: miohansen

capabilityclient/info.go

@@ -0,0 +1,25 @@
+package capabilityclient
+
+import (
+	"fmt"
+	"io"
+	"os"
+)
+
+// PrintAIInfo writes a one-line summary of the active AI provider and model to w.
+// Reads CTX_AI_PROVIDER and CTX_AI_MODEL from the container environment
+// (both injected by ctx from the manifest's ai_provider: and per-extension model: fields).
+// Writes nothing when neither variable is set.
+// Call once per command, before AI work begins.
+func PrintAIInfo(w io.Writer) {
+	provider := os.Getenv("CTX_AI_PROVIDER")
+	model := os.Getenv("CTX_AI_MODEL")
+	if provider == "" && model == "" {
+		return
+	}
+	if model != "" {
+		fmt.Fprintf(w, "ctx: using %s (%s)\n", provider, model)
+	} else {
+		fmt.Fprintf(w, "ctx: using %s\n", provider)
+	}
+}

capabilityclient/info_test.go

@@ -0,0 +1,48 @@
+package capabilityclient_test
+
+import (
+	"bytes"
+	"testing"
+
+	"github.com/delegateas/ctx-sdk/capabilityclient"
+)
+
+func TestPrintAIInfo_ProviderAndModel(t *testing.T) {
+	t.Setenv("CTX_AI_PROVIDER", "claude")
+	t.Setenv("CTX_AI_MODEL", "claude-haiku-4-5")
+
+	var buf bytes.Buffer
+	capabilityclient.PrintAIInfo(&buf)
+
+	got := buf.String()
+	want := "ctx: using claude (claude-haiku-4-5)\n"
+	if got != want {
+		t.Errorf("PrintAIInfo() = %q; want %q", got, want)
+	}
+}
+
+func TestPrintAIInfo_ProviderOnly(t *testing.T) {
+	t.Setenv("CTX_AI_PROVIDER", "claude")
+	t.Setenv("CTX_AI_MODEL", "")
+
+	var buf bytes.Buffer
+	capabilityclient.PrintAIInfo(&buf)
+
+	got := buf.String()
+	want := "ctx: using claude\n"
+	if got != want {
+		t.Errorf("PrintAIInfo() = %q; want %q", got, want)
+	}
+}
+
+func TestPrintAIInfo_NeitherSet(t *testing.T) {
+	t.Setenv("CTX_AI_PROVIDER", "")
+	t.Setenv("CTX_AI_MODEL", "")
+
+	var buf bytes.Buffer
+	capabilityclient.PrintAIInfo(&buf)
+
+	if buf.Len() != 0 {
+		t.Errorf("PrintAIInfo() wrote %q; want empty", buf.String())
+	}
+}