From d54147cfb4a5307fba6a9d75b761bce9062b8a6c Mon Sep 17 00:00:00 2001
From: David Gwilliam <dhgwilliam@gmail.com>
Date: Mon, 16 Mar 2026 21:59:52 -0700
Subject: [PATCH] fix: DisplayStage dependency and render pipeline data flow
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Critical fix for display rendering:

1. DisplayStage Missing Dependency
   - DisplayStage had empty dependencies, causing it to execute before render
   - No data was reaching the display output
   - Fix: Add 'render.output' dependency so display comes after render stages
   - Now proper execution order: source → render → display

2. create_default_pipeline Missing Render Stage
   - Default pipeline only had source and display, no render stage between
   - Would fail validation with 'Missing render.output' capability
   - Fix: Add SourceItemsToBufferStage to convert items to text buffer
   - Now complete data flow: source → render → display

3. Updated Test Expectations
   - test_display_stage_dependencies now expects 'render.output' dependency

Result: Display backends (pygame, terminal, websocket) now receive proper
rendered text buffers and can display output correctly.

Tests: All 502 tests passing
---
 engine/pipeline/adapters.py   | 2 +-
 engine/pipeline/controller.py | 8 +++++++-
 tests/test_adapters.py        | 4 ++--
 3 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/engine/pipeline/adapters.py b/engine/pipeline/adapters.py
index 4b96789..7a9ba3c 100644
--- a/engine/pipeline/adapters.py
+++ b/engine/pipeline/adapters.py
@@ -111,7 +111,7 @@ class DisplayStage(Stage):
 
     @property
     def dependencies(self) -> set[str]:
-        return set()
+        return {"render.output"}  # Display needs rendered content
 
     def init(self, ctx: PipelineContext) -> bool:
         w = ctx.params.viewport_width if ctx.params else 80
diff --git a/engine/pipeline/controller.py b/engine/pipeline/controller.py
index 6810a66..d72b7bd 100644
--- a/engine/pipeline/controller.py
+++ b/engine/pipeline/controller.py
@@ -520,7 +520,10 @@ def create_pipeline_from_params(params: PipelineParams) -> Pipeline:
 def create_default_pipeline() -> Pipeline:
     """Create a default pipeline with all standard components."""
     from engine.data_sources.sources import HeadlinesDataSource
-    from engine.pipeline.adapters import DataSourceStage
+    from engine.pipeline.adapters import (
+        DataSourceStage,
+        SourceItemsToBufferStage,
+    )
 
     pipeline = Pipeline()
 
@@ -528,6 +531,9 @@ def create_default_pipeline() -> Pipeline:
     source = HeadlinesDataSource()
     pipeline.add_stage("source", DataSourceStage(source, name="headlines"))
 
+    # Add render stage to convert items to text buffer
+    pipeline.add_stage("render", SourceItemsToBufferStage(name="items-to-buffer"))
+
     # Add display stage
     display = StageRegistry.create("display", "terminal")
     if display:
diff --git a/tests/test_adapters.py b/tests/test_adapters.py
index 32680fd..3bd7024 100644
--- a/tests/test_adapters.py
+++ b/tests/test_adapters.py
@@ -97,10 +97,10 @@ class TestDisplayStage:
         assert "display.output" in stage.capabilities
 
     def test_display_stage_dependencies(self):
-        """DisplayStage has no dependencies."""
+        """DisplayStage depends on render.output."""
         mock_display = MagicMock()
         stage = DisplayStage(mock_display, name="terminal")
-        assert stage.dependencies == set()
+        assert "render.output" in stage.dependencies
 
     def test_display_stage_init(self):
         """DisplayStage.init() calls display.init() with dimensions."""