Improve Compile Rate

# Depyler Single-Shot Compile Rate: Autonomous Improvement Loop

## Goal
Reach 80% single-shot compile rate on reprorusted-python-cli corpus. Work through bugs autonomously.

## Measure First
```bash
cd /home/noah/src/reprorusted-python-cli
make corpus-retranspile
make corpus-e2e-rate

If >= 80%, report success and stop.

Iteration Loop

1. Find Top Error

cd /home/noah/src/reprorusted-python-cli
uv run python scripts/measure_compile_rate.py --json | jq -r '.failing[].error' | sort | uniq -c | sort -rn | head -5

2. Investigate

Find a failing example, read its Python source and generated Rust. Understand the gap.

3. Fix in depyler

Locations:

• Module mappings → crates/depyler-core/src/direct_rules.rs
• Type mappings → crates/depyler-core/src/type_mapper.rs
• Expr generation → crates/depyler-core/src/rust_gen/expr_gen.rs
• Cargo.toml → crates/depyler-core/src/cargo_toml_gen.rs

4. Validate

cd /home/noah/src/depyler
cargo test -p depyler-core
cargo clippy -p depyler-core -- -D warnings

If fails: git checkout -- . and try different approach.

5. Measure Impact

cargo install --path crates/depyler --force
cd /home/noah/src/reprorusted-python-cli
make corpus-retranspile && make corpus-e2e-rate

If regression: rollback. If no change: still commit (may help other metrics).

6. Commit

git add -A && git commit -m "fix(core): [description] (Refs #193)"

7. Repeat until 80%

Bug Recovery

Issue	Action
Tests fail	Rollback, try narrower fix
Regression	Rollback, add guards
Same error 3x	Skip, move to next pattern
Transpile drops	Rollback, fix is too broad

Priority Errors (from corpus analysis)

1. cannot find value os - 16 files
2. cannot find function date - 10 files
3. expected value, found crate tempfile - 8 files
4. SCRIPT defined multiple times - 5 files

Exit

• SUCCESS: Rate >= 80%
• STUCK: No progress 5 iterations
• BLOCKED: Can't fix failing tests