feat: add GPT/Codex execution discipline guidance for tool persistence (#5414)

Adds OPENAI_MODEL_EXECUTION_GUIDANCE — XML-tagged behavioral guidance
injected for GPT and Codex models alongside the existing tool-use
enforcement. Targets four specific failure modes:

- <tool_persistence>: retry on empty/partial results instead of giving up
- <prerequisite_checks>: do discovery/lookup before jumping to final action
- <verification>: check correctness/grounding/formatting before finalizing
- <missing_context>: use lookup tools instead of hallucinating

Follows the same injection pattern as GOOGLE_MODEL_OPERATIONAL_GUIDANCE
for Gemini/Gemma models. Inspired by OpenClaw PR #38953 and OpenAI's
GPT-5.4 prompting guide patterns.

tests/agent/test_prompt_builder.py

@@ -23,6 +23,7 @@ from agent.prompt_builder import (
     DEFAULT_AGENT_IDENTITY,
     TOOL_USE_ENFORCEMENT_GUIDANCE,
     TOOL_USE_ENFORCEMENT_MODELS,
+    OPENAI_MODEL_EXECUTION_GUIDANCE,
     MEMORY_GUIDANCE,
     SESSION_SEARCH_GUIDANCE,
     PLATFORM_HINTS,
@@ -1021,6 +1022,41 @@ class TestToolUseEnforcementGuidance:
         assert isinstance(TOOL_USE_ENFORCEMENT_MODELS, tuple)
 
 
+class TestOpenAIModelExecutionGuidance:
+    """Tests for GPT/Codex-specific execution discipline guidance."""
+
+    def test_guidance_covers_tool_persistence(self):
+        text = OPENAI_MODEL_EXECUTION_GUIDANCE.lower()
+        assert "tool_persistence" in text
+        assert "retry" in text
+        assert "empty" in text or "partial" in text
+
+    def test_guidance_covers_prerequisite_checks(self):
+        text = OPENAI_MODEL_EXECUTION_GUIDANCE.lower()
+        assert "prerequisite" in text
+        assert "dependency" in text
+
+    def test_guidance_covers_verification(self):
+        text = OPENAI_MODEL_EXECUTION_GUIDANCE.lower()
+        assert "verification" in text or "verify" in text
+        assert "correctness" in text
+
+    def test_guidance_covers_missing_context(self):
+        text = OPENAI_MODEL_EXECUTION_GUIDANCE.lower()
+        assert "missing_context" in text or "missing context" in text
+        assert "hallucinate" in text or "guess" in text
+
+    def test_guidance_uses_xml_tags(self):
+        assert "<tool_persistence>" in OPENAI_MODEL_EXECUTION_GUIDANCE
+        assert "</tool_persistence>" in OPENAI_MODEL_EXECUTION_GUIDANCE
+        assert "<verification>" in OPENAI_MODEL_EXECUTION_GUIDANCE
+        assert "</verification>" in OPENAI_MODEL_EXECUTION_GUIDANCE
+
+    def test_guidance_is_string(self):
+        assert isinstance(OPENAI_MODEL_EXECUTION_GUIDANCE, str)
+        assert len(OPENAI_MODEL_EXECUTION_GUIDANCE) > 100
+
+
 # =========================================================================
 # Budget warning history stripping
 # =========================================================================