Attach images to posts and return the Telegram message id

The adapter response now carries telegram_message_id and a t.me/c link.
compose visual resolves a post's image: own visual_url, else the entry's
rendered portrait, else hold an entry with only a visual prompt, else the
HelixForge main image. send-post.sh resolves before touching credentials,
requires an image on public posts and runs the adapter with ATTACH_VISUAL.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Assistant: claude-code
Assistant-Model: opus
Assistant-Process: 5457@bnt-lap001
Assistant-Session: 792bf84a-3783-4f5d-a811-cded61dd2012

internal/compose/visual_test.go

@@ -0,0 +1,74 @@
+package compose
+
+import "testing"
+
+const hallRaw = "https://forge.example/coulomb/hall-of-helix/raw/branch/main"
+const fallback = "https://forge.example/coulomb/pr-hall-of-helix/raw/branch/main/assets/helix-forge.png"
+
+func TestResolveVisualPrefersRenderedPortrait(t *testing.T) {
+	entry := "# Seat\n\n## Visual prompt\n\n> Constellation dialect.\n\n![Tegwick at work](../visuals/bernd-how-it-started.png)\n\n## Handoff\n"
+	v, err := ResolveVisual(entry, hallRaw, fallback)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if v.Kind != VisualPortrait || v.Path != "visuals/bernd-how-it-started.png" ||
+		v.URL != hallRaw+"/visuals/bernd-how-it-started.png" {
+		t.Fatalf("got %+v", v)
+	}
+}
+
+func TestResolveVisualPromptWithoutPortraitNeedsRender(t *testing.T) {
+	entry := "# Seat\n\n## Visual prompt\n\n> Constellation dialect. Square.\n> Brass scales.\n\n" +
+		"<!-- ![scales](../visuals/claude-x-scales.jpg) -->\n\n" +
+		"_Draft: portrait not yet rendered, expected as `claude-x-scales.jpg`._\n\n## Handoff\n"
+	v, err := ResolveVisual(entry, hallRaw, fallback)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if v.Kind != VisualNeedsRender || v.URL != "" {
+		t.Fatalf("a commented-out portrait or the fallback was used: %+v", v)
+	}
+	if v.Prompt != "Constellation dialect. Square. Brass scales." {
+		t.Fatalf("prompt = %q", v.Prompt)
+	}
+	if v.Target != "visuals/claude-x-scales.jpg" {
+		t.Fatalf("target = %q", v.Target)
+	}
+}
+
+func TestResolveVisualFallsBackOnlyWithoutPrompt(t *testing.T) {
+	for _, entry := range []string{"", "# Seat\n\n## Handoff\n\nNothing visual.\n"} {
+		v, err := ResolveVisual(entry, hallRaw, fallback)
+		if err != nil {
+			t.Fatal(err)
+		}
+		if v.Kind != VisualFallback || v.URL != fallback {
+			t.Fatalf("entry %q: got %+v", entry, v)
+		}
+	}
+	if _, err := ResolveVisual("", hallRaw, ""); err == nil {
+		t.Fatal("resolved with no fallback configured")
+	}
+}
+
+func TestResolveVisualIgnoresExternalImages(t *testing.T) {
+	entry := "# Seat\n\n![badge](https://img.example/visuals/x.png)\n"
+	v, err := ResolveVisual(entry, hallRaw, fallback)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if v.Kind != VisualFallback {
+		t.Fatalf("got %+v", v)
+	}
+}
+
+func TestResolveVisualTargetFromBareFileName(t *testing.T) {
+	entry := "# Seat\n\n## Visual prompt\n\n> Scales.\n\n_Draft: expected under `visuals/` as `claude-y-scales.jpg`._\n"
+	v, err := ResolveVisual(entry, hallRaw, fallback)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if v.Target != "visuals/claude-y-scales.jpg" {
+		t.Fatalf("target = %q", v.Target)
+	}
+}