[Milestone] minishell v1.0.0 Core Launch 🚀

[shonakam]

🎯 Mission

Implement and integrate a robust shell environment following the GNU Bash execution model. This milestone covers the end-to-end lifecycle of a command: from interactive input (Readline) and lexical/syntactic analysis (Lexer/Parser) to process orchestration (Executor) and internal state management (Session/Builtins).

🏗 System Architecture

• Session: Context initialization, Environment management, Signal handling.
• Lexer: FSM-based tokenization, Operator & Word recognition.
• Parser: Recursive descent parsing, AST construction (Pipeline, Logical, Subshell).
• Executor: Process orchestration, Redirection, Word expansion, Job control.
• Builtins: All mandatory internal commands with POSIX compliance.
• Readline: Interactive CLI, History management, Signal-safe prompt.

🚀 Execution Flow (The Lifecycle)

Input → Lexer → Parser → Expander → Redirector → Executor → Wait & Cleanup

🔭 Scope (Target Features)

Syntax & Operators

• Pipelines: Parallel execution of commands connected by |.
• Subshells: Independent execution environments encapsulated within ( ).
• Logical Operators: Support for short-circuit evaluation using && and ||.
• Background Execution: Asynchronous command execution using the & operator.

Redirection

• Standard I/O: Input (<), Output (>), and Append (>>) redirections.
• Heredocument: Pre-processing and temporary storage for << operators.

Word Expansion

• Environment Variables: Expansion of $VAR and special parameter $?.
• Wildcards (Pattern Matching): Pathname expansion for the * character.
• Quote Removal: Handling of literal strings within ' ' and " ".

🛠 Technical Constraints

• Zero Memory Leaks: Maintain a leak-free codebase verified by valgrind or ASan/leaks. Every allocated block must be properly deallocated before the process exits or loops.

• Strict FD Management: Ensure all pipe and file descriptors are closed immediately after their required lifecycle. Prevent "too many open files" errors by managing FD inheritance during fork.

• High Robustness: The system must remain stable under all circumstances. Invalid inputs or syntax errors must be caught gracefully, providing informative error messages without crashing the shell.

• Signal Integrity: Maintain consistent shell behavior during signal interruptions (e.g., SIGINT, SIGQUIT), ensuring the prompt returns correctly and child processes are handled as expected.