Fix Gemini protocol status codes and error handling

- Path security violations now return 51 (Not Found) instead of 59 (Bad Request)
- Timeouts return 41 (Server Unavailable) per Gemini spec
- Add comprehensive request validation: empty requests, oversized requests (>1024 bytes), malformed URLs
- Fix CLI argument conflict (config -c vs cert -c)
- Update documentation with status codes, error handling guidelines, and lint checking
- Add environment setup instructions for clippy and cargo PATH

AGENTS.md

@@ -11,7 +11,9 @@ nothing else. It is meant to be generic so other people can use it.
 - `cargo test` - Run all unit tests
 - `cargo test <test_name>` - Run a specific test
 - `cargo test <module>::tests` - Run tests in a specific module
-- `cargo clippy` - Run linter checks
+- `cargo clippy` - Run linter checks for code quality
+- `cargo clippy --fix` - Automatically fix clippy suggestions
+- `cargo clippy --bin <name>` - Check specific binary
 - `cargo fmt` - Format code according to Rust standards
 - `cargo check` - Quick compile check without building
 
@@ -64,6 +66,16 @@ nothing else. It is meant to be generic so other people can use it.
 - Test security boundaries (path traversal, invalid inputs)
 - Use `assert_eq!` and `assert!` for validations
 
+## Lint Checking
+- `cargo clippy` - Run linter checks for code quality
+- `cargo clippy --fix` - Automatically fix clippy suggestions
+- `cargo clippy --bin <name>` - Check specific binary
+- `cargo fmt` - Format code to match Rust standards
+- **Run clippy before every commit** - Address all warnings before pushing code
+- Current clippy warnings (2025-01-15):
+  - src/server.rs:16-17 - Unnecessary borrows on file_path
+  - src/logging.rs:31 - Match could be simplified to let statement
+
 ## Async Patterns
 - Use `.await` on async calls
 - Prefer `tokio::fs` over `std::fs` in async contexts
@@ -73,11 +85,24 @@ nothing else. It is meant to be generic so other people can use it.
 ## Gemini Protocol Specific
 - Response format: "STATUS META\r\n"
 - Status 20: Success (follow with MIME type)
-- Status 51: Not found
-- Status 59: Bad request
+- Status 41: Server unavailable (timeout, overload)
+- Status 51: Not found (resource doesn't exist)
+- Status 59: Bad request (malformed URL, protocol violation)
 - Default MIME: "text/gemini" for .gmi files
 - Default file: "index.gmi" for directory requests
 
+## Error Handling
+- **Timeout**: Return status 41 "Server unavailable" (not 59)
+- **Request too large**: Return status 59 "Bad request"
+- **Empty request**: Return status 59 "Bad request"  
+- **Invalid URL format**: Return status 59 "Bad request"
+- **Hostname mismatch**: Return status 59 "Bad request"
+- **Path resolution failure**: Return status 51 "Not found" (including security violations)
+- **File not found**: Return status 51 "Not found"
+- Reject requests > 1024 bytes (per Gemini spec)
+- Reject requests without proper `\r\n` termination
+- Use `tokio::time::timeout()` for request timeout handling
+
 ## Configuration
 - TOML config files with `serde::Deserialize`
 - CLI args override config file values
@@ -94,3 +119,8 @@ nothing else. It is meant to be generic so other people can use it.
 - Default port: 1965 (standard Gemini port)
 - Default host: 0.0.0.0 for listening
 - Log level defaults to "info"
+
+## Environment Setup
+- Install clippy: `rustup component add clippy`
+- Ensure `~/.cargo/bin` is in PATH (add `source "$HOME/.cargo/env"` to `~/.bashrc`)
+- Verify setup: `cargo clippy --version`