feat(vision): vision_analyze returns pixels to vision-capable models, not aux text (#22955)

When the active main model has native vision and the provider supports
multimodal tool results (Anthropic, OpenAI Chat, Codex Responses, Gemini
3, OpenRouter, Nous), vision_analyze loads the image bytes and returns
them to the model as a multimodal tool-result envelope. The model then
sees the pixels directly on its next turn instead of receiving a lossy
text description from an auxiliary LLM.

Falls back to the legacy aux-LLM text path for non-vision models and
unverified providers.

Mirrors the architecture used in OpenCode, Claude Code, Codex CLI, and
Cline. All four converge on the same pattern: tool results carry image
content blocks for vision-capable provider/model combinations.

Changes
- tools/vision_tools.py: _vision_analyze_native fast path + provider
  capability table (_supports_media_in_tool_results). Schema description
  updated to reflect new behaviour.
- agent/codex_responses_adapter.py: function_call_output.output now
  accepts the array form for multimodal tool results (was string-only).
  Preflight validates input_text/input_image parts.
- agent/auxiliary_client.py: _RUNTIME_MAIN_PROVIDER/_MODEL globals so
  tools see the live CLI/gateway override, not the stale config.yaml
  default. set_runtime_main()/clear_runtime_main() helpers.
- run_agent.py: AIAgent.run_conversation calls set_runtime_main at turn
  start so vision_analyze's fast-path check sees the actual runtime.
- tests/conftest.py: clear runtime-main override between tests.

Tests
- tests/tools/test_vision_native_fast_path.py: provider capability
  table, envelope shape, fast-path gating (vision-capable model uses
  fast path; non-vision model falls through to aux).
- tests/run_agent/test_codex_multimodal_tool_result.py: list tool
  content becomes function_call_output.output array; preflight
  preserves arrays and drops unknown part types.

Live verified
- Opus 4.6 + Sonnet 4.6 on OpenRouter: model calls vision_analyze on a
  typed filepath, gets pixels back, reads exact text from images that
  no aux description could capture (font color irony, multi-line
  fruit-count list, etc.).

PR replaces the closed prior efforts (#16506 shipped the inbound user-
attached path; this PR closes the gap for tool-discovered images).

tests/tools/test_vision_native_fast_path.py

@@ -0,0 +1,207 @@
+"""Tests for the native-vision fast path inside vision_analyze.
+
+When the active main model supports native vision AND the provider supports
+image content inside tool-result messages, ``_handle_vision_analyze`` skips
+the auxiliary LLM and returns a multimodal envelope so the main model sees
+the pixels directly on its next turn.
+"""
+
+from __future__ import annotations
+
+import asyncio
+import base64
+import json
+from pathlib import Path
+from unittest.mock import patch
+
+import pytest
+
+from tools.vision_tools import (
+    _build_native_vision_tool_result,
+    _handle_vision_analyze,
+    _supports_media_in_tool_results,
+    _vision_analyze_native,
+)
+
+
+# Minimal valid 1x1 PNG bytes.
+_TINY_PNG = base64.b64decode(
+    b"iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAQAAAC1HAwCAAAAC0lEQVR42mNkYAAAAAYAAjCB0C8AAAAASUVORK5CYII="
+)
+
+
+# ─── _supports_media_in_tool_results ─────────────────────────────────────────
+
+
+class TestSupportsMediaInToolResults:
+    def test_anthropic_native_yes(self):
+        assert _supports_media_in_tool_results("anthropic", "claude-opus-4-6") is True
+
+    def test_openrouter_yes(self):
+        assert _supports_media_in_tool_results("openrouter", "anthropic/claude-opus-4.6") is True
+
+    def test_nous_yes(self):
+        assert _supports_media_in_tool_results("nous", "anthropic/claude-sonnet-4.6") is True
+
+    def test_openai_chat_yes(self):
+        assert _supports_media_in_tool_results("openai", "gpt-5.4") is True
+
+    def test_openai_codex_yes(self):
+        assert _supports_media_in_tool_results("openai-codex", "gpt-5-codex") is True
+
+    def test_gemini_3_yes(self):
+        assert _supports_media_in_tool_results("google", "gemini-3-flash-preview") is True
+
+    def test_gemini_2_no(self):
+        assert _supports_media_in_tool_results("google", "gemini-2.5-pro") is False
+
+    def test_unknown_provider_conservative_no(self):
+        assert _supports_media_in_tool_results("brand-new-provider", "any-model") is False
+
+    def test_empty_provider_no(self):
+        assert _supports_media_in_tool_results("", "anything") is False
+        assert _supports_media_in_tool_results(None, "anything") is False  # type: ignore[arg-type]
+
+
+# ─── _build_native_vision_tool_result ────────────────────────────────────────
+
+
+class TestBuildNativeVisionToolResult:
+    def test_envelope_shape(self):
+        env = _build_native_vision_tool_result(
+            image_url="/tmp/foo.png",
+            question="what does it say?",
+            image_data_url="data:image/png;base64,XYZ",
+            image_size_bytes=1024,
+        )
+        assert env["_multimodal"] is True
+        assert isinstance(env["content"], list)
+        assert len(env["content"]) == 2
+        assert env["content"][0]["type"] == "text"
+        assert env["content"][1]["type"] == "image_url"
+        assert env["content"][1]["image_url"]["url"] == "data:image/png;base64,XYZ"
+        assert "what does it say?" in env["content"][0]["text"]
+        assert "Image attached natively" in env["text_summary"]
+
+    def test_no_question_omits_question_section(self):
+        env = _build_native_vision_tool_result(
+            image_url="/tmp/foo.png",
+            question="",
+            image_data_url="data:image/png;base64,XYZ",
+            image_size_bytes=512,
+        )
+        text = env["content"][0]["text"]
+        assert "Question:" not in text
+        assert "Image loaded" in text
+
+
+# ─── _vision_analyze_native ──────────────────────────────────────────────────
+
+
+class TestVisionAnalyzeNative:
+    def test_local_file_returns_multimodal_envelope(self, tmp_path):
+        img = tmp_path / "test.png"
+        img.write_bytes(_TINY_PNG)
+        result = asyncio.get_event_loop().run_until_complete(
+            _vision_analyze_native(str(img), "what is this?")
+        )
+        assert isinstance(result, dict)
+        assert result.get("_multimodal") is True
+        parts = result["content"]
+        assert any(p.get("type") == "image_url" for p in parts)
+        assert any(p.get("type") == "text" for p in parts)
+        url = next(p["image_url"]["url"] for p in parts if p.get("type") == "image_url")
+        assert url.startswith("data:image/")
+
+    def test_missing_file_returns_error_string(self, tmp_path):
+        result = asyncio.get_event_loop().run_until_complete(
+            _vision_analyze_native(str(tmp_path / "nope.png"), "?")
+        )
+        # tool_error returns a JSON string, not the multimodal envelope
+        assert isinstance(result, str)
+        parsed = json.loads(result)
+        assert parsed.get("success") is False
+        assert "Invalid image source" in parsed.get("error", "")
+
+    def test_empty_image_url_returns_error(self):
+        result = asyncio.get_event_loop().run_until_complete(
+            _vision_analyze_native("", "?")
+        )
+        assert isinstance(result, str)
+        parsed = json.loads(result)
+        assert parsed.get("success") is False
+        assert "image_url is required" in parsed.get("error", "")
+
+    def test_file_url_scheme_resolves(self, tmp_path):
+        img = tmp_path / "t.png"
+        img.write_bytes(_TINY_PNG)
+        result = asyncio.get_event_loop().run_until_complete(
+            _vision_analyze_native(f"file://{img}", "?")
+        )
+        assert isinstance(result, dict)
+        assert result.get("_multimodal") is True
+
+
+# ─── _handle_vision_analyze fast-path gating ─────────────────────────────────
+
+
+class TestHandleVisionAnalyzeFastPath:
+    """Verify the dispatcher chooses fast-path vs aux-LLM correctly."""
+
+    def test_vision_capable_main_model_uses_fast_path(self, tmp_path, monkeypatch):
+        """Main model supports native vision → fast path returns multimodal."""
+        img = tmp_path / "x.png"
+        img.write_bytes(_TINY_PNG)
+
+        # Set runtime override so the handler thinks we're on opus@openrouter
+        from agent.auxiliary_client import set_runtime_main, clear_runtime_main
+        set_runtime_main("openrouter", "anthropic/claude-opus-4.6")
+        try:
+            coro = _handle_vision_analyze({"image_url": str(img), "question": "?"})
+            result = asyncio.get_event_loop().run_until_complete(coro)
+        finally:
+            clear_runtime_main()
+
+        assert isinstance(result, dict), \
+            f"Expected multimodal envelope, got {type(result).__name__}: {str(result)[:200]}"
+        assert result.get("_multimodal") is True
+
+    def test_non_vision_main_model_falls_through_to_aux(self, tmp_path, monkeypatch):
+        """Non-vision main model → fast path skipped, aux LLM path attempted."""
+        img = tmp_path / "x.png"
+        img.write_bytes(_TINY_PNG)
+
+        async def _aux_sentinel(*args, **kwargs):
+            return '{"sentinel": "aux-path"}'
+
+        from agent.auxiliary_client import set_runtime_main, clear_runtime_main
+        set_runtime_main("openrouter", "qwen/qwen3-coder")
+        try:
+            with patch("tools.vision_tools.vision_analyze_tool", side_effect=_aux_sentinel):
+                coro = _handle_vision_analyze({"image_url": str(img), "question": "?"})
+                result = asyncio.get_event_loop().run_until_complete(coro)
+        finally:
+            clear_runtime_main()
+
+        assert not (isinstance(result, dict) and result.get("_multimodal") is True), \
+            "Fast path fired for non-vision model; should have fallen through to aux LLM"
+
+    def test_fast_path_disabled_for_unsupported_provider(self, tmp_path, monkeypatch):
+        """Even with vision-capable model, unknown provider → fall through."""
+        img = tmp_path / "x.png"
+        img.write_bytes(_TINY_PNG)
+
+        async def _aux_sentinel(*args, **kwargs):
+            return '{"sentinel": "aux-path"}'
+
+        from agent.auxiliary_client import set_runtime_main, clear_runtime_main
+        set_runtime_main("brand-new-provider", "anthropic/claude-opus-4.6")
+        try:
+            with patch("tools.vision_tools.vision_analyze_tool", side_effect=_aux_sentinel):
+                coro = _handle_vision_analyze({"image_url": str(img), "question": "?"})
+                result = asyncio.get_event_loop().run_until_complete(coro)
+        finally:
+            clear_runtime_main()
+
+        assert not (isinstance(result, dict) and result.get("_multimodal") is True), \
+            "Fast path fired for unknown provider; should have fallen through"