Add comprehensive research documentation for level system feature

[flora131]

Summary

• Add comprehensive research documentation covering the existing codebase architecture, patterns, and data models
• Include detailed Product Requirements Document (PRD) for a level system with obstacles feature
• Provide step-by-step implementation plan with code examples and integration points
• Add manual testing strategy with 50+ test cases

Documentation Overview

Core Codebase Documentation

Document	Description
architecture.md	System overview and design patterns
directory-structure.md	File organization and module layout
tech-stack.md	Technology choices and tooling
entry-points.md	Execution flow and initialization
patterns.md	Coding conventions and patterns
data-models.md	Data structures and type system
dependencies.md	External library analysis

Level System Feature Documentation

Document	Description
level-system-with-obstacles-prd.md	Product Requirements Document
implementation-plan-level-system.md	Detailed implementation guide
integration-points.md	Exact code modification locations
testing-strategy-level-system.md	Manual testing procedures

Total: 13 documents (~84 KB) providing complete guidance for implementing the level system feature.

Test plan

• Verify all markdown files render correctly on GitHub
• Confirm internal links between documents work
• Check code examples for syntax correctness

🤖 Generated with Claude Code

[Copilot]

Pull request overview

This PR adds a set of research/architecture documents for the existing rust-snake codebase and provides a full PRD + implementation/testing guidance for a proposed “level system with obstacles” feature.

Changes:

• Added core codebase documentation (architecture, directory structure, entry points, patterns, data models, dependencies, tech stack).
• Added feature planning docs for “level system with obstacles” (PRD, implementation plan, integration points).
• Added a manual testing strategy document and a timestamped architecture research note under research/docs/.

Reviewed changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated 9 comments.

Show a summary per file

File	Description
research/architecture.md	High-level architecture summary for the current codebase
research/directory-structure.md	Documents repo and src/ layout
research/tech-stack.md	Lists language/tooling/dependencies used
research/entry-points.md	Describes runtime flow (main loop + module entry points)
research/patterns.md	Captures observed coding patterns and conventions
research/data-models.md	Describes core structs/enums and data/state flow
research/dependencies.md	Dependency inventory and analysis
research/level-system-with-obstacles-prd.md	PRD for the proposed level/obstacle feature
research/implementation-plan-level-system.md	Step-by-step implementation plan with integration details
research/integration-points.md	Maps exact suggested code touchpoints for the feature
research/testing-strategy-level-system.md	Manual test plan/checklists for validating the feature
research/docs/2026-02-07-architecture-overview.md	Timestamped architecture research report
research/README.md	Index/reading paths and summary of the documentation set

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[Copilot]

This says piston_window is “Fixed at 0.123.0”. In Cargo.toml it’s specified as piston_window = "0.123.0", which is a semver requirement (allows patch updates within 0.123.x), not an exact pin. Please reword to describe the actual range or use an exact requirement (=0.123.0) if you truly want to pin.

Suggested change

	- **piston_window**: Fixed at 0.123.0
	- **piston_window**: Caret requirement `0.123.0` (allows 0.123.x patch updates)

[Copilot]

The note that piston_window “doesn't have built-in text rendering” is misleading: piston_window supports text rendering via Glyphs/text, but it requires wiring up a font (TTF) and glyph cache. Please update this section to reflect that the missing piece is font asset/setup (and possibly a helper crate for locating assets), rather than needing a new text-rendering dependency.

Suggested change

	**Note**: piston_window doesn't have built-in text rendering. Two options:
	**Option A: Skip text for MVP**
	- Use colored overlays to indicate level transitions
	- Score tracking works internally without display
	**Option B: Add text dependency**
	- Add `piston_window` text features
	- Or use external crate like `gfx_text` or `rusttype`
	**Recommendation**: Start with **Option A** for MVP, add text in Phase 7 (optional enhancement)
	**Note**: `piston_window` supports text rendering via `Glyphs` and the `text` function, but you must wire up a TTF font asset and a glyph cache (and possibly use a helper crate to locate assets). Two options:
	**Option A: Skip text for MVP**
	- Use colored overlays to indicate level transitions
	- Score tracking works internally without display
	**Option B: Enable text rendering with fonts**
	- Use `piston_window`'s built-in text API (`Glyphs` + `text`) with a bundled TTF font and initialized glyph cache
	- Optionally add a small helper crate for asset discovery (e.g., locating the `assets/` directory); external text-rendering crates like `gfx_text` or `rusttype` are optional, not required
	**Recommendation**: Start with **Option A** for MVP, then in Phase 7 add text by wiring up a font asset and glyph cache using `piston_window`'s text APIs

[Copilot]

The “Documentation Statistics” table lists filenames that don’t exist in this PR (e.g., level-system-prd.md, implementation-plan.md, testing-strategy.md). Please rename these entries to the actual filenames (e.g., level-system-with-obstacles-prd.md, implementation-plan-level-system.md, testing-strategy-level-system.md) so the table is accurate.

Suggested change

	| level-system-prd.md | 4.5 KB | Requirements | Product/Dev |
	| implementation-plan.md | 15 KB | Code Changes | Implementers |
	| integration-points.md | 11 KB | Modification Locations | Implementers |
	| testing-strategy.md | 14 KB | Validation | QA/Implementers |
	| level-system-with-obstacles-prd.md | 4.5 KB | Requirements | Product/Dev |
	| implementation-plan-level-system.md | 15 KB | Code Changes | Implementers |
	| integration-points.md | 11 KB | Modification Locations | Implementers |
	| testing-strategy-level-system.md | 14 KB | Validation | QA/Implementers |

[Copilot]

The “Total: ~84 KB across 11 documents” summary is likely inaccurate given this PR adds 12+ markdown files (plus research/docs/...). Please update the document count/total size (or remove the exact totals) to avoid the README becoming misleading as docs evolve.

Suggested change

	**Total**: ~84 KB of documentation covering ~252 lines of existing code + ~246 lines planned
	These documents collectively cover the existing codebase and the planned level system work in depth.

[Copilot]

The summary claims the codebase follows “clean, idiomatic Rust patterns,” which is subjective and conflicts with the stated documentation principle of being purely factual. Consider rephrasing this summary to describe concrete observed patterns (naming, module layout, constants, guard clauses, etc.) without value judgments.

Suggested change

	This codebase follows **clean, idiomatic Rust patterns**:
	- Clear naming conventions
	- Struct-based encapsulation
	- Constants for configuration
	- Early returns for guards
	- Pattern matching for enums
	- No defensive error handling (assumes correct usage)
	The following patterns are observed in this codebase:
	- Clear naming conventions
	- Struct-based encapsulation
	- Constants for configuration
	- Early returns for guards
	- Pattern matching for enums
	- Limited defensive error handling; many operations rely on correct usage

[Copilot]

Cargo.toml does not specify a Rust edition, so the crate edition defaults to 2015 (it’s not dependent on the Cargo version). Please adjust this line to state the 2015 default, or explicitly mention that adding edition = "2021" would make the intent unambiguous.

Suggested change

	- **Edition**: Not explicitly specified (defaults to 2015 or 2018 based on Cargo version)
	- **Edition**: Not explicitly specified in `Cargo.toml` (defaults to the 2015 edition; adding `edition = "2021"` would make the intent unambiguous)

[Copilot]

This document says the piston_window version is “fixed at 0.123.0”. In Cargo, specifying "0.123.0" is a caret requirement by default (for 0.x it allows patch updates <0.124.0), not an exact pin. Either reword this to describe the actual semver range, or use an exact requirement (=0.123.0) if the intent is to pin.

Suggested change

	- Fixed at 0.123.0 (exact version)
	- Relatively modern version
	- No caret (^) or tilde (~) versioning
	- Specified as `0.123.0` in `Cargo.toml` (Cargo caret requirement)
	- Effective semver range: `>=0.123.0, <0.124.0` (allows 0.123.x patch updates)
	- Relatively modern version

[Copilot]

The “No Known CVEs” section makes an unqualified security claim (“No known critical vulnerabilities …”). Without a date/source this will become stale and may be incorrect. Suggest qualifying it (e.g., “as of ”), linking to a vulnerability source, or removing the assertion and sticking to verifiable properties (no network input, no secrets, etc.).

Suggested change

	### No Known CVEs
	- No known critical vulnerabilities in rand 0.8 or piston_window 0.123.0
	- Both are mature, maintained libraries
	### Vulnerability Status (as of 2026-02-07)
	- As of 2026-02-07, no critical vulnerabilities were listed for `rand` 0.8 or `piston_window` 0.123.0 in the RustSec advisory database (https://rustsec.org/)
	- This may change over time; check RustSec or your distribution’s advisory database for the latest vulnerability information
	- Both are widely used and actively maintained libraries, but maturity and maintenance do **not** guarantee the absence of vulnerabilities

[Copilot]

This README ends with “Last Updated: 2024-02-05”, but this PR adds new/updated research (including a 2026-02-07 doc). Please update the date to reflect the current update or remove it if it can’t be kept in sync.

Suggested change

	**Last Updated**: 2024-02-05
	**Last Updated**: 2026-02-07