Revert "feat(ecc): prune plugin 43→12 items, promote 7 rules to .claude/rules/ (#245)"

This reverts commit 1bd68ff534.

.cursor/rules/common-performance.md

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+---
+description: "Performance optimization: model selection strategy, context window management, extended thinking"
+alwaysApply: true
+---
+
+# Performance Optimization
+
+## Model Selection Strategy
+
+**Haiku 4.5** (90% of Sonnet capability, 3x cost savings):
+- Lightweight agents with frequent invocation
+- Pair programming and code generation
+- Worker agents in multi-agent systems
+
+**Sonnet 4.5** (Best coding model):
+- Main development work
+- Orchestrating multi-agent workflows
+- Complex coding tasks
+
+**Opus 4.5** (Deepest reasoning):
+- Complex architectural decisions
+- Maximum reasoning requirements
+- Research and analysis tasks
+
+## Context Window Management
+
+Avoid last 20% of context window for:
+- Large-scale refactoring
+- Feature implementation spanning multiple files
+- Debugging complex interactions
+
+Lower context sensitivity tasks:
+- Single-file edits
+- Independent utility creation
+- Documentation updates
+- Simple bug fixes
+
+## Extended Thinking + Plan Mode
+
+Extended thinking is enabled by default, reserving up to 31,999 tokens for internal reasoning.
+
+Control extended thinking via:
+- **Toggle**: Option+T (macOS) / Alt+T (Windows/Linux)
+- **Config**: Set `alwaysThinkingEnabled` in `~/.claude/settings.json`
+- **Budget cap**: `export MAX_THINKING_TOKENS=10000`
+- **Verbose mode**: Ctrl+O to see thinking output
+
+For complex tasks requiring deep reasoning:
+1. Ensure extended thinking is enabled (on by default)
+2. Enable **Plan Mode** for structured approach
+3. Use multiple critique rounds for thorough analysis
+4. Use split role sub-agents for diverse perspectives
+
+## Build Troubleshooting
+
+If build fails:
+1. Use **build-error-resolver** agent
+2. Analyze error messages
+3. Fix incrementally
+4. Verify after each fix