#11226: Fix system property assignment in cache-trace.ts

There is a discrepancy between "session:loaded" and "stream:context" that makes it appear as though no context is sent to the LLM ```json { "stage": "session:loaded", "ts": "2026-02-07T13:08:09.286Z", "provider": "gamecuboid", "modelApi": "openai-responses", "modelId": "gpt-oss:esther", "systemType": "string", "systemLen": 36436, "hasProject": true, "hasSoul": true, "systemHead": "You are a personal assistant running inside OpenClaw.\n## Tooling\nTool availability (filtered by policy):\nTool names are case-sensitive. Call tools exactly as li" } { "stage": "stream:context", "ts": "2026-02-07T13:08:09.333Z", "provider": "gamecuboid", "modelApi": "openai-responses", "modelId": "gpt-oss:esther", "systemType": "null", "systemLen": 0, "hasProject": false, "hasSoul": false, "systemHead": "" } ``` This held true with both responses and completions APIs After changing to context.systemPrompt, the output matches along both steps ```json { "stage": "session:loaded", "ts": "2026-02-07T15:02:10.242Z", "provider": "gamecuboid", "modelApi": "openai-responses", "modelId": "gpt-oss:esther", "systemType": "string", "systemLen": 36436, "hasProject": true, "hasSoul": true, "systemHead": "You are a personal assistant running inside OpenClaw.\n## Tooling\nTool availability (filtered by policy):\nTool names are case-sensitive. Call tools exactly as li" } { "stage": "stream:context", "ts": "2026-02-07T15:02:10.251Z", "provider": "gamecuboid", "modelApi": "openai-responses", "modelId": "gpt-oss:esther", "systemType": "string", "systemLen": 36436, "hasProject": true, "hasSoul": true, "systemHead": "You are a personal assistant running inside OpenClaw.\n## Tooling\nTool availability (filtered by policy):\nTool names are case-sensitive. Call tools exactly as li" } ``` This should make debugging with the cache-trace more accurate <!-- greptile_comment --> <h2>Greptile Overview</h2> <h3>Greptile Summary</h3> This change updates cache trace logging for the `stream:context` stage to read the system prompt from `context.systemPrompt` (falling back to `context.system`) so the recorded `system` value matches what was present when the session was loaded, improving trace accuracy when debugging LLM context issues. <h3>Confidence Score: 2/5</h3> - This PR should not be merged as-is because it introduces a syntax error that will break builds. - The core functional intent is small and localized, but `cache-trace.ts` now contains an extra comma in an object literal, which is a guaranteed compile/runtime failure until fixed. - src/agents/cache-trace.ts <!-- greptile_other_comments_section --> _{(2/5) Greptile learns from your feedback when you react with thumbs up/down!} <!-- /greptile_comment -->