fix: resolve user templates in remote PPTX generation

CHANGELOG.md

@@ -10,6 +10,16 @@ Entries before v0.5.0 were written retroactively as summaries.
 
 ## [Unreleased]
 
+### Fixed
+
+- **AWS: uploaded custom templates now apply to PPTX generation** — the remote
+  server's template resolution only searched builtin templates, so a deck
+  referencing an uploaded user template silently fell back to
+  `blank-dark.pptx`. Generation now resolves user templates first (same order
+  as `analyze_template`), and an unresolvable template name raises an explicit
+  error listing available templates instead of silently using the wrong
+  design. (#206)
+
 ## [0.7.0] - 2026-08-03
 
 ### Added

servers/remote/tools/generate.py

@@ -248,13 +248,31 @@ def _collect_import_refs(value: object) -> set[str]:
         tmpl_name = ""  # signal: resolved
     if tmpl_name:
         normalized = tmpl_name.removesuffix(".pptx")
-        for t in storage.list_templates():
-            if t.get("name") == normalized:
-                template_key = t.get("s3Key", "")
-                break
+        # User templates take precedence (same order as analyze_template).
+        if storage.get_user_template_metadata(user_id, normalized):
+            template_path.write_bytes(
+                storage.download_user_template(user_id, normalized)
+            )
+        else:
+            for t in storage.list_templates():
+                if t.get("name") == normalized:
+                    template_key = t.get("s3Key", "")
+                    break
+            if not template_key:
+                # Do NOT silently fall back to a stock template: the deck
+                # explicitly references a template, so building with a
+                # different one would silently produce the wrong design.
+                available = [t.get("name", "") for t in storage.list_templates()]
+                available += [
+                    t.get("name", "") for t in storage.list_user_templates(user_id)
+                ]
+                raise ValueError(
+                    f"Template '{tmpl_name}' not found. "
+                    f"Available: {', '.join(available)}"
+                )
     if not template_path.exists():
         if not template_key:
-            template_key = deck.get("templateS3Key", "templates/blank-dark.pptx")
+            template_key = "templates/blank-dark.pptx"
         template_path.write_bytes(storage.download_file(key=template_key))
 
     # Fonts

tests/test_mcp_generate.py

@@ -27,12 +27,12 @@ def mock_storage():
     """Storage mock materializing a one-slide deck."""
     storage = MagicMock()
     storage.pptx_bucket = "pptx-bucket"
-    storage.get_deck.return_value = {
-        "deckId": "d1", "name": "Test", "templateS3Key": "templates/blank-dark.pptx",
-    }
+    storage.get_deck.return_value = {"deckId": "d1", "name": "Test"}
     storage.get_deck_json.return_value = {
         "template": "", "fonts": {"fullwidth": "", "halfwidth": ""},
     }
+    storage.get_user_template_metadata.return_value = None
+    storage.list_user_templates.return_value = []
 
     def list_files(prefix: str, bucket: str = ""):
         if prefix.endswith("/slides/"):
@@ -81,3 +81,50 @@ def test_generate_pptx_missing_deck(mock_storage):
     mock_storage.get_deck.return_value = None
     with pytest.raises(ValueError, match="not found"):
         generate_mod.generate_pptx(deck_id="dX", user_id="u1", storage=mock_storage)
+
+
+def test_prepare_workspace_resolves_user_template(mock_storage):
+    """A deck referencing an uploaded user template uses it (Issue #206)."""
+    mock_storage.get_deck_json.return_value = {
+        "template": "my-brand.pptx", "fonts": {"fullwidth": "", "halfwidth": ""},
+    }
+    mock_storage.get_user_template_metadata.return_value = {
+        "name": "my-brand", "s3Key": "user-templates/u1/my-brand.pptx",
+    }
+    mock_storage.download_user_template.return_value = _TEMPLATE.read_bytes()
+
+    tmpdir, _slides, build_kwargs = generate_mod._prepare_workspace(
+        "d1", "u1", mock_storage,
+    )
+
+    mock_storage.get_user_template_metadata.assert_called_once_with("u1", "my-brand")
+    mock_storage.download_user_template.assert_called_once_with("u1", "my-brand")
+    assert build_kwargs["template_path"].read_bytes()[:2] == b"PK"
+    # Builtin download path must not be used for the template
+    for call in mock_storage.download_file.call_args_list:
+        assert not call.kwargs.get("key", "").startswith("templates/")
+
+
+def test_prepare_workspace_unknown_template_raises(mock_storage):
+    """An unresolvable template name fails loudly instead of silently
+    falling back to blank-dark (Issue #206)."""
+    mock_storage.get_deck_json.return_value = {
+        "template": "ghost.pptx", "fonts": {"fullwidth": "", "halfwidth": ""},
+    }
+    mock_storage.list_templates.return_value = [
+        {"name": "blank-dark", "s3Key": "templates/blank-dark.pptx"},
+    ]
+    mock_storage.list_user_templates.return_value = [{"name": "my-brand"}]
+
+    with pytest.raises(ValueError, match=r"'ghost\.pptx' not found.*blank-dark.*my-brand"):
+        generate_mod._prepare_workspace("d1", "u1", mock_storage)
+
+
+def test_prepare_workspace_empty_template_defaults_to_blank_dark(mock_storage):
+    """No template specified → blank-dark default (regression guard)."""
+    tmpdir, _slides, build_kwargs = generate_mod._prepare_workspace(
+        "d1", "u1", mock_storage,
+    )
+
+    mock_storage.download_file.assert_any_call(key="templates/blank-dark.pptx")
+    assert build_kwargs["template_path"].read_bytes()[:2] == b"PK"