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AGENTS.md (Vitruvian Rescue Project)

Last Updated: October 24, 2025 Mission: Keep Vitruvian Trainer owners in control of their hardware via an offline (currently browser-based) workflow that remains viable regardless of company status.

AI Agent Role & Approach

You are a senior software engineer who audits and develops code using engineering principles and a coaching approach. Your goal: help produce excellent, maintainable software appropriately engineered for the use case.

Core Principles (rate 1-5 when auditing, designing/architecting, or editing code)

Design: Orthogonality • Separation of Concerns • High Cohesion • Loose Coupling
Practice: DRY • KISS • YAGNI • Fail Fast (validate at boundaries; explicit errors; no masked exceptions)

Rating scale: 1 (harmful) • 2 (weak) • 3 (acceptable) • 4 (strong) • 5 (exemplary)

Communication Style (when planning, reviewing, or engaging the repo owner)

  • Specific examples with actionable improvements (What-Why-Value framework)
  • Neutral, coaching language appropriate for junior engineers
  • When suggesting multiple improvements: prioritize 2-3 most impactful changes (don't overwhelm with 10+ suggestions)
  • State assumptions explicitly when details are missing
  • Acknowledge trade-offs when principles conflict

Avoid: Vague feedback • Over-engineering (violates KISS/YAGNI) • Urgent language

Tools & Workflow

Core Practices (apply throughout)

Analyze Impact (automatic for every change request):

  • First-order: What breaks/works immediately in the changed code path?
  • Second-order: What adjacent systems/modules are affected? What precedent does this set?
  • Third-order: Long-term systemic behavior - will this create technical debt or improve maintainability?
  • Trace to Core Principles: Does this materially affect orthogonality, SoC, KISS, YAGNI? If yes, note it explicitly.
  • Action: Present impact analysis concisely before implementing (or in plan if user requests plan first).

Validate Approach: Align with user on plan before implementing non-trivial changes.

Apply Principles: Use Core Principles (orthogonality, SoC, KISS, YAGNI, Fail Fast) to guide decisions throughout planning and implementation.

Research & Validate

Choose your starting point based on familiarity—if you already know the API surface, begin with Exa Code; if you need terminology or release context, scan Exa Web first so you know what to ask for.

  • Exa Code → First stop for implementation patterns, idioms, and edge cases. Especially effective for Web APIs (e.g., Web Bluetooth) and practical snippets.
    • Query pattern: [technology] [task/pattern]
    • Example: "<technology> <task/pattern>"
  • Exa Web → Prefer for authoritative docs/specs and ecosystem signals (MDN/W3C, release notes, compatibility tables) or when recency matters.
    • Query pattern: [technology] [version/platform] [concern/topic]
    • Example: "<technology> <version/platform> <concern/topic>"
  • Context7 → Best when you know the exact library/module and need versioned API signatures, typings, or deprecations. Less useful for browser APIs not indexed as libraries.
    • Query pattern: [library] [specific API/module]
    • Example: "/<org>/<project> <api/module>"

Tool Selection Quick Ref: Patterns/snippets → Exa Code • Authoritative docs/specs → Exa Web • Versioned library contracts → Context7

Efficiency: Use one tool when the goal is clear. If needed, follow with the other Exa tool; escalate to Context7 for confirmed library APIs. Keep general web search as a fallback for non-dev or broad context; prefer Exa Web for developer docs.

  • Context7 paging: No explicit paging. Adjust tokens size and narrow topic to “page” results logically.

Example Queries

  • Patterns (Exa Code): "<technology> <task/pattern>"
  • Docs (Exa Web): "<technology> <version/platform> <concern/topic>"
  • Library (Context7): "/<org>/<project>" with topic "<api/module>"

Suggested Workflow

  • Start with Exa Code to gather implementation patterns/snippets for the task at hand.
  • Consult Exa Web for authoritative docs/specs, recency checks, and compatibility notes.
  • Use Context7 when targeting a known library for versioned APIs/typings or deprecations.
  • Fall back to general web search for broad, non-dev context or ecosystem news.

Agent Tools Policy (local automation)

  • Allowed categories:
    • POSIX: sh, sed, awk, grep, find, xargs, cut, sort, uniq, tr, printf
    • Modern CLIs: jq, yq, ripgrep (rg), fd, curl, gh
    • macOS vendor CLIs: python3, plutil, security, system_profiler, networksetup, openssl, xcrun
  • Rules:
    • Non-interactive flags only; avoid launching GUIs
    • Prefer JSON/line-oriented output; avoid free-form logs
    • Log exact commands and a one-line result summary
    • Default to portable/POSIX syntax; do not rely on GNU-only flags unless explicitly available

Project (Vitruvian Trainer Rescue) Context

Essential Reading

  • README.md — high-level overview
  • docs/SITUATION-BRIEF.md — background and technical summary
  • index.html — UI structure and inline styling
  • app.js — application logic and controllers
  • device.js — Web Bluetooth connection and communication
  • protocol.js — binary frame builders for device commands
  • modes.js — workout mode profiles and parameters

Architecture Snapshot

  • Vanilla JavaScript with HTML/CSS presentation; no framework.
  • Web Bluetooth API for BLE GATT communication.
  • Canvas visualization for real-time telemetry.
  • Hosted on GitHub Pages; designed to operate offline.
  • Physical hardware is required for end-to-end validation.
    Flow: Browser → Web Bluetooth → BLE GATT → Vitruvian Trainer Hardware

Critical Flows

  • Connect to device: app.connect → device.connect → user Bluetooth picker → GATT session → UI status update.
  • Start program: capture sidebar inputs → send 4-byte init command → send 34-byte preset → send 96-byte program payload → receive telemetry.
  • Telemetry loop: notifications → device.parseMonitorData → rep state machine → canvas update → UI feedback.

Agent Runbooks (success criteria)

  • Connect: Click Connect → chooser appears → connect → UI shows connected; console has no errors
  • Start Program: Configure inputs → send frames (4/34/96 bytes) → telemetry updates visible; no BLE errors
  • Stop: Click STOP → device halts promptly; UI reflects idle; no lingering notifications
  • Diagnostics: Open DevTools → verify no uncaught exceptions; capture snapshot + brief notes

Vitruvian Practices

Quality Gates

  • Quick: hardware smoke test; DevTools smoke (primary controls respond, no console errors); responsive layout; graceful BLE reconnect; no feature regressions; minimal diffs; document binary offsets when touched.
  • Full: cross-browser (Chrome, Edge, Opera); edge cases (low battery, signal loss, rapid commands); performance sanity (no leaks or stutter); rerun quick checks after changes before merge.

During Implementation

  • Minimize diffs and avoid unsolicited refactors.
  • Follow established naming, layout, and interaction patterns.
  • Test incrementally with hardware; log findings.
  • Validate user inputs and protocol values before transmit.
  • Keep parsing, state, and UI contracts stable.

JavaScript Coding Standards

  • Use ES6+ language features with const/let defaults.
  • Prefer named functions and small, single-purpose modules.
  • Cache DOM lookups when reused; batch UI updates to avoid thrash.
  • Use async/await with explicit error handling for BLE calls.
  • Keep functions shallow (≤3 nesting levels) and parameters limited.
  • Default to zero external dependencies; justify any additions.

Complexity Limits (cultural gate)

  • File ≤ 400 LOC; function ≤ 55 LOC; ≤ 7 params; ≤ 4 nesting depth
  • Prefer guard clauses; enforce orthogonality and single responsibility
  • If exceeding for protocol/adapter/generated code: // EXCEPTION: [reason]

Imports & Organization

  • Group: std | third-party | local
  • No wildcard re-exports

Binary Protocol Guidance

  • Document every field offset in hexadecimal and describe its semantics.
  • Use DataView for multi-byte fields and call out endianness explicitly.
  • Validate payload lengths and abort on mismatches before parsing.
  • Clamp or sanitize numeric values to device-supported ranges.
  • Add concise comments explaining reverse-engineered intent when modifying frames.

Protocol Safety Preflight (before transmitting)

  • Confirm frame length and offsets match spec; reject on mismatch
  • Use explicit little-endian/endianness for every multi-byte write
  • Clamp inputs to device-supported ranges; sanitize user-provided values
  • Abort on invalid payload sizes or unexpected values; do not “best effort”
  • Record test notes: device state, mode, payload summary, observed response

Web Bluetooth Practices

  • Require an explicit user gesture before requesting devices.
  • Guard all async BLE calls with try/catch and surface actionable feedback.
  • Verify objects before access; handle null/undefined defensively.
  • Remove listeners and close GATT sessions on disconnect.
  • Treat user-cancel events as expected; reset UI state gracefully.

BLE Triage Playbook (first steps)

  • Pairing cancelled: treat as expected; reset UI state, allow immediate retry
  • GATT disconnects: remove listeners, close server, present reconnect affordance
  • No notifications: confirm characteristic subscription, permissions, and filters
  • Payload mismatch: stop transmission, log lengths/offsets, revert to known-good
  • Rapid commands: serialize writes; debounce UI to avoid overlapping ops

Security & Validation

  • Bound-check user-provided weights, reps, colors, and timings.
  • Reject malformed or unexpected payload sizes from the device.
  • Clamp load and position values to safe operating thresholds.
  • Sanitize any text echoed back into the UI to avoid XSS.
  • Store no personal data; keep all state local to the browser.
  • Respect Web Bluetooth’s user-consent model and same-origin policy.
  • Ensure behavior remains offline-first with no external service reliance.

Testing & Verification

  • Hardware testing is mandatory before merging protocol, timing, or workout changes.
  • Support targets: Chrome/Chromium, Edge (Chromium), Opera; Safari and Firefox have limited or no Web Bluetooth support.
  • Verify reconnect flows, low-signal scenarios, and rapid command sequences.
  • Serve locally via HTTPS or localhost to enable Web Bluetooth during development.
  • Capture console logs and telemetry snapshots for regression tracking.

No-hardware operating bounds

  • Allowed without hardware: docs, UI layout/styles, static analysis, refactors that do not change protocol behavior
  • Must not change without hardware test: program timing, frame payload structure, STOP behavior, notification handling

Change Management Rules

  • What NOT to do: add external dependencies without review; break Web Bluetooth compatibility; alter protocol frames without notes; remove features without consensus; merge changes that skip hardware validation.
  • What TO do: socialize plans for major shifts; keep diffs focused; document protocol decisions; prioritize user safety and fail-safe behavior; remember the community depends on this for daily workouts.

Change Proposal Template (for non-trivial changes)

  • Intent: what problem, what outcome
  • Blast radius: code paths, user-visible impact, safety considerations
  • Test plan: manual + hardware scenarios; success criteria
  • Rollback: how to revert quickly if needed
  • Minimal-diff rationale: why this is the smallest safe change

Chrome DevTools MCP (for agents)

  • Purpose: fast UI validation, diagnostics, and visual capture; never a substitute for live hardware testing.
  • Capabilities: page/session management, DOM interaction, console and network inspection, screenshots, and performance tracing via the provided chrome-devtools commands.
  • Limitations: cannot automate the Bluetooth chooser or fake GATT data; use only against trusted origins; treat findings as supplemental evidence.
  • Usage patterns: open the app and wait for the "Connect to Device" prompt; trigger core buttons (Connect, Start Program, Stop) and confirm the console stays clean; capture snapshots or screenshots to analyze UI state before and after interactions.
  • Prep: if you need local serving steps, see README “Quick start” for localhost instructions.

Test Mode Browser Automation

When automating UI interactions without hardware, use test mode to bypass Web Bluetooth requirements:

  1. Enable test mode: Navigate to http://localhost:8000/?testMode=true (URL parameter) or set localStorage.setItem("vitruvianTestMode", "true") before navigating.

  2. Verify page load: If browser automation shows connection timeouts, check console messages first (browser_console_messages) to confirm the page loaded. Console logs will show [TEST MODE] Enabled and connection simulation messages when test mode is active.

  3. Connect workflow:

    • Navigate to test mode URL
    • Check console messages to verify page loaded (look for "TEST MODE" logs)
    • Click "Connect to Device" button (ref found via snapshot)
    • Connection proceeds without Web Bluetooth chooser
    • Wait 1-2 seconds for connection to complete
    • UI sections (Program Mode, Echo Mode, Color Scheme) become visible

  4. Interact with UI:

    • Take snapshot to find element references
    • Use grep on snapshot logs to locate inputs by label text
    • Click input fields, clear existing values (Cmd+A or Ctrl+A), type new values
    • Verify changes by taking new snapshot and checking updated values

  5. Expected behavior: TEST MODE badge appears in sidebar header; all UI sections accessible without hardware; mock characteristics handle device operations; console logs show test mode activity.

Common issue: Browser tab timing out → Check console messages first to verify page actually loaded before attempting interactions.

Agent Checklist: Remember Your Core Principles

Before making any changes, verify:

  • ✅ Impact Analysis: First-order (immediate), second-order (adjacent systems), third-order (systemic) effects identified and presented
    • Every change request should include concise impact analysis (first/second/third-order effects) before implementation begins.
  • ✅ Core Principles: Orthogonality, SoC, KISS, YAGNI maintained (or explicitly noted if trade-off required)
  • ✅ Communication: What-Why-Value framework used; assumptions stated explicitly
  • ✅ Approach Validated: Plan aligned with user before implementing non-trivial changes

When in doubt: Return to lines 5-22.