docs: add AGENT.md and update compression engine module

AGENT.md

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+# Agent Configuration
+
+**IMPORTANT:** Prefer to use the `write_file` tool if the edit is for the majority of a file, or if you are correcting previous problems made edits from other tools.
+
+## Commands
+
+**IMPORTANT:** Always export `TERM=dumb`.
+**IMPORTANT:** The cargo command cannot be ran in parallel.
+
+### Build
+- Build: `TERM=dumb cargo build`
+- Build release: `TERM=dumb cargo build --release`
+
+### Test
+- Run all tests: `TERM=dumb cargo test`
+- Run specific test: `TERM=dumb cargo test TEST_NAME`
+- Run tests with output: `TERM=dumb cargo test -- --nocapture`
+
+### Lint/Format Commands
+- Check formatting: `TERM=dumb cargo fmt --check`
+- Format code: `TERM=dumb cargo fmt`
+- Lint: `TERM=dumb cargo clippy`
+- Lint with errors: `TERM=dumb cargo clippy -- -D warnings`
+
+## Code Style Guidelines
+
+### Imports
+- Group imports in order: standard library, external crates, local modules
+- Use explicit imports over glob imports (`use std::fs::File;` not `use std::fs::*;`)
+
+### Formatting
+- Use rustfmt (configured via rustfmt.toml if exists)
+- Max line length: 100 characters
+- Indent with 4 spaces
+
+### Types
+- Prefer explicit types in public API
+- Use `&str` for string literals, `String` for owned strings
+- Use `Option<T>` for optional values, `Result<T, E>` for error handling
+
+### Naming Conventions
+- Use snake_case for variables and functions
+- Use PascalCase for types and traits
+- Use UPPER_SNAKE_CASE for constants and statics
+
+### Error Handling
+- Use `anyhow::Result` for most error handling
+- Use `anyhow::Context` to add context to errors
+- Avoid `unwrap()` in production code
+
+### Documentation
+- Document all public APIs with rustdoc
+- Use examples in documentation when helpful
+
+## Procedures
+
+### Fix build problems
+
+Use this plan with sequential thinking:
+- Check the project using `TERM=dumb cargo check`
+- Identify the cause of any errors and warnings
+- If there are no errors or warnings, stop
+- If there are errors are warnings, create a plan to fix errors and warnings
+- Fix the files one at a time, not in parallel
+- Use the `write_file` tool to output the complete version of the corrected file