Bug type: Regression (worked before, now fails)

Beta release blocker: No

Summary: Long sessions with heavy tool usage frequently produce [openclaw] missing tool result in session history; inserted synthetic error result for transcript repair warnings, eventually crashing the ongoing task with ⚠️ Something went wrong while processing your request. This occurred occasionally on 2026.4.15 but became dramatically more frequent on 4.29–5.4, happening almost every time a task involves multiple sequential tool calls. Reverting to 2026.4.15 reduces it back to occasional.

Steps to reproduce:

1. Start a session on any version between 4.29–5.4
2. Engage in a long task requiring many sequential tool calls (exec, write, read, etc.)
3. Observe missing tool result in session history warnings in gateway logs during tool-intensive turns
4. After enough tool calls accumulate, the current task crashes with Something went wrong
5. The session itself is not dead — normal chat can continue, but the interrupted task is lost

Expected behavior: Long sessions with heavy tool usage should complete reliably. On 2026.4.15, missing tool result occurred only occasionally; the same workloads on 4.29+ fail almost every time.

Actual behavior: Two co-occurring symptoms:

• Frequent missing tool result in session history; inserted synthetic error result for transcript repair log entries
• After sufficient tool call accumulation, the ongoing task terminates with ⚠️ Something went wrong while processing your request. Please try again, or use /new to start a fresh session.
• The session is not fully dead — normal conversation can resume, but the task in progress is interrupted and cannot recover.
• These appear correlated: tool result loss seems to cascade into the task failure.

OpenClaw version: 2026.4.29 / 5.3 / 5.4 (all affected — very frequent) / 2026.4.15 (occasionally affected, but much more stable)

Operating system: WSL2 (Ubuntu) on Windows 11

Install method: npm global

Model: zai/glm-5-turbo, deepseek/deepseek-v4-flash (both affected)

Provider / routing chain: openclaw → zai (direct API) / openclaw → deepseek (direct API)

Additional provider/model setup details: Also reproduced with deepseek/deepseek-v4-flash (openclaw → deepseek direct API). zai-light is a custom provider definition (same base URL as zai, different API key) and was NOT used during reproduction.

May be related to #77642.