[Bug] Write tool silently fails when tool_use truncated by max_tokens limit

Bug Description
Title: Write tool silently fails with "missing content" when tool_use hits max_tokens limit (hard 8k output ceiling)

Body:

Reproducible bug in Claude Code where Write tool invocations with large content parameters fail with InputValidationError: The required parameter 'content' is missing, even though the model is correctly attempting to pass content.

Root cause (verified from session jsonl): assistant responses have an 8000 output token ceiling. When the model generates a large content parameter inside a tool_use block, it can hit stop_reason=max_tokens before the content field is emitted. The API closes out the tool_use block with file_path only, and the harness rejects it as missing required param.

Evidence from session 2fa0be29-8f59-413b-89a0-ae522a8b9bd9 (2026-04-08):

• Successful EN Write, 18 077 chars: stop_reason=tool_use, output_tokens=7 900
• 11 consecutive failures on Ukrainian translation (~18 000 chars, ~30 000 tokens due to Cyrillic BPE density): all stop_reason=max_tokens, output_tokens=8 000
• A diagnostic Write(content="test") between failures succeeded → rules out file/encoding/tool bugs
• Retry loop makes it worse (context grows, budget unchanged)

Expected behavior (at least one of):

1. Surface the real error to the model: "tool_use truncated by max_tokens — retry with smaller content or use Edit for partial updates" instead of generic "missing content"
2. Auto-suggest chunking: harness could detect stop_reason=max_tokens inside tool_use and provide actionable guidance
3. Allow Write to stream content across multiple turns / raise output ceiling for tool_use blocks
4. Client-side heuristic: warn model when file target size exceeds safe threshold

User impact: especially bad for non-English content (Cyrillic, CJK) where token density is 3× English — files that "look normal" in characters blow the budget. User ends up in frustrating retry loops until they manually instruct chunking.

Environment Info

• Platform: win32
• Terminal: windows-terminal
• Version: 2.1.96
• Feedback ID: 1b2d7c7d-e262-414f-9fe0-4be98ff56e47

Errors

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