feat(cosh): add large paste placeholder and fix placeholder id reset on esc cancel

[kongld-mq]

Description

feat(cosh): add large paste placeholder and fix placeholder id reset on esc cancel

• Create placeholder for pastes >1000 chars or >10 lines instead of full content
• Support sequential IDs for multiple pastes of same size with reuse mechanism
• Atomically delete placeholder on Backspace
• Expand placeholder to full content on submit
• Use pasteWorkaround check for macOS Enter-fix to prevent double-submit
• Handle clipboard errors with debugLogger instead of console.error
• Clear pendingPastes and activePlaceholderIds on double ESC to reset ID counter
• Add 9 new test cases covering placeholder creation, expansion, deletion, reuse, and ESC reset
• Fix enter-submit on macOS: only apply recentPasteTime protection when
  pasteWorkaround is enabled (Windows or Node < 20). On macOS/Linux with
  modern Node, bracketed paste markers work reliably so the protection is
  unnecessary and caused the first Enter after paste to be ignored.

Related Issue

closes #

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Refactoring (no functional change)
• Performance improvement
• CI/CD or build changes

Scope

• cosh (copilot-shell)
• sec-core (agent-sec-core)
• skill (os-skills)
• sight (agentsight)
• Multiple / Project-wide

Checklist

• I have read the Contributing Guide
• My code follows the project's code style
• I have added tests that prove my fix is effective or that my feature works
• I have updated the documentation accordingly
• For cosh: Lint passes, type check passes, and tests pass
• For sec-core (Rust): cargo clippy -- -D warnings and cargo fmt --check pass
• For sec-core (Python): Ruff format and pytest pass
• For skill: Skill directory structure is valid and shell scripts pass syntax check
• For sight: cargo clippy -- -D warnings and cargo fmt --check pass
• Lock files are up to date (package-lock.json / Cargo.lock)

Testing

After generating the test text, paste it into the input box

large text test(>1000 chars)

python3 -c "print('A' * 1500)"

Multi-line test (>10 lines)

for i in {1..15}; do echo "Line $i"; done

Small text test(<1000 chars)

python3 -c "print('A' * 500)"

Additional Notes

大文本粘贴	粘贴 1500 字符	显示 [Pasted Content 1500 chars]
多行粘贴	粘贴 15 行	显示 [Pasted Content XX chars]
小文本粘贴	粘贴 500 字符	正常显示完整文本
多次粘贴	连续粘贴两次 1001 字符	第二次显示 #2
Backspace	粘贴后按 Backspace	整体删除占位符

[gemini-code-assist]

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[samchu-zsl]

Summary

非常棒的功能扩展 🎉 —— 大粘贴占位符、ID 复用、ESC 重置整体思路清晰，测试用例也覆盖了主要正向路径。以下留下 4 条具体改动建议，按建议处理后整体可以合入：

🟡 Major（建议修复）

• UTF-16 vs code-point 偏移混用（InputPrompt.tsx L878-L892）：backspace 删除占位符的路径里，buffer.lines[i].length 与 text.slice 走 UTF-16，而 buffer.cursor 的 col 和 replaceRangeByOffset 走 code-point，混用后只要用户在占位符前输入了 emoji 等非 BMP 字符就会错位。
• 占位符被部分删除后原文静默丢失（InputPrompt.tsx L867-L907）：当前仅匹配「光标恰好在占位符尾」，若用户按 ← 进入占位符内部或从下一行回退再 backspace，占位符字符串被逐字破坏，而 pendingPastes 仍持有完整 key，提交时正则匹配失败，用户拿到残缺占位符而非原文。
• recentPasteTime gating 语义变化缺测试（InputPrompt.tsx L798）：加了 pasteWorkaround && 后，原来的 paste-auto-submission 保护测试因为默认 pasteWorkaround=false，实际已经不再走到保护分支了；建议补一条 pasteWorkaround=true 下的回归测试。

ℹ️ Minor

• 占位符文案硬编码（InputPrompt.tsx L179）：同文件已经 import { t }，建议走 i18n。

感谢贡献！