zero/docs/PRD.md

Zero — Product Requirements Document (v1.0)

Status: DRAFT v1.0 Target: Compete with Claude Code + Cursor + OpenCode Timeline: 6-12 months Stack: Go native core + npm distribution wrapper

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1. Vision

Zero is a terminal-first, editor-aware, multi-provider AI coding platform.

It combines the best of:

• Claude Code — terminal-native agentic coding
• Cursor — IDE integration + smart editing
• OpenCode — multi-provider + headless

One Go-native agent core. Three surfaces. Zero lock-in.

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2. Core Surfaces

2.1 Terminal (TUI) — Primary

• Interactive coding agent in terminal
• Streaming, append-style (like Claude Code)
• Bubble Tea + Lip Gloss-based
• Full keyboard control
• Mouse support

2.2 Editor (VS Code Extension)

• Same agent core, different UI
• Inline suggestions + chat panel
• File editing with diff view
• Diagnostics integration
• LSP-aware

2.3 Headless (CLI/CI)

• zero exec "prompt" for scripts
• zero serve for daemon mode
• JSON-RPC over stdio/WebSocket
• MCP server support

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3. Architecture

┌─────────────────────────────────────────────────┐
│              ZERO PLATFORM                        │
├─────────────────────────────────────────────────┤
│                                                  │
│  ┌──────────┐  ┌──────────┐  ┌──────────┐     │
│  │   TUI    │  │   VSCode │  │ Headless │     │
│  │ Surface  │  │ Surface  │  │ Surface  │     │
│  └────┬─────┘  └────┬─────┘  └────┬─────┘     │
│       │             │             │            │
│       └─────────────┼─────────────┘            │
│                     │                          │
│              ┌──────▼──────┐                   │
│              │  Agent Core │                   │
│              │  (ReAct)    │                   │
│              └──────┬──────┘                   │
│                     │                          │
│  ┌──────┬──────┬────┴────┬──────┬──────┐      │
│  │Tools │Perms │Sessions │Provi │Memory│      │
│  └──────┴──────┴─────────┴──────┴──────┘      │
│                                                  │
└─────────────────────────────────────────────────┘

Layering Rules:

• Agent Core never imports a surface
• Surfaces are thin shells (I/O + rendering)
• All state persists to local files
• No cloud dependency

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4. Functional Requirements (24 Features)

F1 — Agent Core (P0)

• ReAct loop: think → tool → result → think
• Stream text + tool calls + thinking
• Parallel tool execution where safe
• Bound turns (max 100)
• Clean interrupt (Esc/Ctrl-C)
• Event stream: text | tool_call | tool_result | thinking | usage | plan_update | error | turn_end

F2 — Tools (P0)

Core (8):

• read_file — read with line ranges, images
• write_file — create/overwrite
• edit_file — exact-string edit (uniqueness guard)
• bash — run shell command
• grep — ripgrep content search
• glob — file pattern matching
• apply_patch — multi-hunk patches
• update_plan — todo list

Advanced (4):

• web_fetch / web_search — web access
• task — spawn subagent
• structured_output — JSON-Schema validated
• notebook_edit — Jupyter notebooks

Tool Requirements:

• Go typed parameter schemas -> JSON Schema
• Side-effect class: read | write | shell | network | out_of_workspace
• Structured results: { status, output, truncated?, meta? }
• Atomic execution
• Permission gating

F3 — Providers & Model Registry (P0)

• OpenAI-compatible (works with OpenAI, OpenRouter, Ollama, etc.)
• Anthropic (Claude)
• Google Gemini
• Azure OpenAI
• AWS Bedrock
• xAI (Grok)

Model Registry:

type ModelEntry struct {
  ID              string
  Name            string
  Provider        string
  APIProviders    []string
  ContextLimits   ContextLimits
  ReasoningEffort ReasoningEffort
  Capabilities    ModelCapabilities
  Cost            ModelCost
  Tier            string
  MatchPatterns   []string
}

• Per-task model selection (-m)
• Provider rotation/failover
• Cost tracking
• "Spec model" for planning
• Fallback model on failure

F4 — Terminal UI (P0)

• Layout: header (cwd · git · model) → tool rows → diff → response → input → footer
• Streaming: append-only transcript model with live tail updates
• Markdown: full CommonMark + syntax highlighting
• Tool rows: collapsible with one-line summaries
• Input: / commands, @ files, ! bash, Esc interrupt
• Robustness: resize, wide-char, ANSI, non-TTY fallback
• Splash: ZERO wordmark
• Themes: light/dark + custom

F5 — Sessions (P0)

• Persist to ~/.local/share/zero/sessions/<id>/
• meta.json + events.jsonl + messages.jsonl + checkpoints/
• --resume [id] (default: latest)
• --fork <id> (copy with lineage)
• Search: zero search <query> over messages/tools/results
• Atomic writes (write-temp-then-rename)
• Schema versioning
• Export to Markdown/JSON

F6 — Configuration (P0)

• Layered: defaults → user → project → env → CLI
• ~/.config/zero/config.json (user)
• ./.zero/config.json (project)
• Runtime overlay (--settings <path>)
• Feature flags for staged rollout
• Validation on load

F7 — MCP (Model Context Protocol) (P0)

• Connect to stdio/HTTP/SSE servers
• Surface MCP tools into registry
• zero mcp add/remove/list
• Per-server and per-tool permissions
• Persistent grants with revoke/clear
• MCP server mode (zero as MCP server)

F8 — Headless / Programmatic (P0)

• zero exec [prompt] — one-shot
• zero serve — daemon mode
• --input-format stream-json — line-delimited events
• --input-format stream-jsonrpc — JSON-RPC protocol
• -o text|json output formats
• Exit codes: 0=success, 1=crash, 2=usage, 3=provider, 4=tool, 5=permission, 6=budget

F9 — Permissions & Autonomy (P0)

• Side-effect classes: read, write, shell, network, out_of_workspace
• Autonomy levels: low (ask), medium (smart), high (auto)
• --skip-permissions-unsafe (loud warning)
• TUI: inline prompts (allow/deny/always)
• Headless: default-deny unless granted
• Persistent grants with list/revoke/clear
• Audit log in events.jsonl

Permission Matrix:

Tool Class	low	medium	high
Read	allow	allow	allow
Workspace write	prompt	allow	allow
Shell	prompt	prompt	allow
Network	prompt	allow	allow
Out-of-workspace	deny	prompt	prompt

F10 — Observability (P0)

• Structured logging (stdout/stderr split)
• Secret redaction (API keys, tokens, passwords)
• No vendor telemetry (local only)
• zero doctor — health check command
• Crash reports (opt-in, local)
• Performance metrics (TTFT, tokens/sec)

F11 — Subagents (P1)

• task tool spawns scoped subagent
• Built-in agents: code-review, security-review, refactor, test-gen
• Recursion depth limit
• Parent session linkage
• Shared/isolated budgets

F12 — Plugins (P1)

• User/project-scoped plugins
• Commands, tools, prompts, hooks
• Plugin manifest: plugin.json
• zero plugin install <path|url>
• No marketplace in v1 (manual install)

F13 — Distribution (P0)

• Single binary via Go cross-compilation
• npm package as a thin installer/launcher for the platform binary
• Cross-platform: Linux, macOS, Windows
• zero update [--check] self-update
• Checksum verification
• Rollback on failure

F14 — VS Code Extension (P1)

• Same agent core via stream protocol
• Inline chat panel
• Diff view in editor
• Diagnostics integration
• LSP awareness
• File watching

F15 — Memory & Context (P1)

• AGENTS.md hierarchical memory
• @import for modular rules
• Auto-generated from init command
• Project conventions learning
• Skills system (reusable instruction packs)
• Context budgeting (token tracking)
• Auto-compaction when full

F16 — Hooks System (P1)

• Lifecycle hooks: PreToolUse, PostToolUse, SessionStart, SessionEnd
• User-defined shell commands
• JSON output for conditional flow
• .zero/hooks/ directory

F17 — Slash Commands (P0)

Built-in (20):

• Session: /clear, /compact, /context, /rewind, /resume, /exit
• Model: /model, /effort, /style, /permissions
• Project: /init, /memory, /skills
• Extensibility: /mcp, /hooks, /agents
• Meta: /help, /config, /doctor, /feedback

Custom: ./.zero/commands/*.md

F18 — Git Integration (P1)

• Worktree isolation per task
• Auto-commit with messages
• Branch management
• PR creation
• Diff review
• Conflict resolution

F19 — Testing & Verification (P1)

• run_tests tool
• Self-verification loop
• Test runner integration
• Coverage reporting
• Diagnostics (typecheck, lint)
• LSP integration

F20 — Web Access (P1)

• web_fetch — fetch URL content
• web_search — search engine
• Provider/permission gated
• Rate limiting
• Caching

F21 — Sandbox (P2)

• Linux: bubblewrap
• macOS: sandbox-exec
• Windows: AppContainer
• Filesystem policies
• Network policies
• Unix socket controls

F22 — Multi-modal (P2)

• Image input (screenshots, diagrams)
• PDF parsing
• Voice input (optional)
• File attachments
• Paste support

F23 — Telemetry (P2)

• Local-only metrics
• Token usage tracking
• Cost reports
• Performance profiling
• Crash reports (opt-in)
• NO vendor telemetry

F24 — Advanced Features (P2)

• Code review automation
• Auto-refactor
• Dependency updates
• Security scanning
• Documentation generation

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5. Data Models

5.1 Headless Event Stream

{ "type": "run_start", "runId": "r1", "sessionId": "s1", "cwd": "/repo", "model": "..." }
{ "type": "text", "delta": "..." }
{ "type": "tool_call", "id": "t1", "name": "bash", "args": {...}, "sideEffect": "shell" }
{ "type": "permission", "id": "t1", "decision": "needs_approval", "reason": "shell" }
{ "type": "tool_result", "id": "t1", "status": "ok", "output": "...", "truncated": false }
{ "type": "usage", "promptTokens": 1234, "completionTokens": 567, "costUsd": 0.012 }
{ "type": "plan_update", "plan": [{ "id": "1", "content": "...", "status": "in_progress" }] }
{ "type": "turn_end", "stopReason": "end_turn" }
{ "type": "error", "code": "rate_limit", "message": "...", "recoverable": true }
{ "type": "run_end", "status": "success", "exitCode": 0 }

5.2 Session On Disk

~/.local/share/zero/sessions/<id>/
  meta.json        # { schemaVersion, id, parentId?, title, cwd, model, createdAt, updatedAt, tokens, cost }
  events.jsonl     # append-only AgentEvent stream
  messages.jsonl   # provider-facing messages
  checkpoints/     # snapshots for restore/fork/compact

5.3 Tool Contract

type Tool interface {
  Name() string
  Description() string
  Parameters() JSONSchema
  SideEffect() SideEffect
  Execute(ctx ToolContext, args map[string]any) ToolResult
}

type ToolResult struct {
  Status    string
  Output    string
  Truncated bool
  Meta      map[string]any
}

5.4 Config Schema

{
  "model": "claude-sonnet-4-6",
  "providers": {
    "anthropic": { "apiKey": "env:AN..._KEY" },
    "openai": { "apiKey": "env:OP..._KEY" }
  },
  "permissions": {
    "autonomy": "medium",
    "grants": [{ "tool": "bash", "pattern": "git status", "decision": "allow" }]
  },
  "ui": { "theme": "dark", "syntaxHighlighting": true }
}

---

6. Non-Functional Requirements

Performance

• TTFT < 500ms after provider's first byte
• No full-transcript repaint per token
• Cold start < 300ms (warm cache)
• Tool execution < 100ms overhead
• Session resume < 1s

Reliability

• Crash-free TUI under resize, wide-char, non-TTY
• Clean interrupt (no half-written state)
• Atomic session writes
• Recovery from malformed JSONL
• Provider failover

Security

• No mutation without permission decision (hard invariant)
• API keys never logged
• Secret redaction everywhere
• Headless stdout free of logs
• Workspace boundary by default
• Sandboxing for untrusted code

Portability

• Linux, macOS, Windows
• Any OpenAI-compatible endpoint
• x86_64, ARM64
• Single binary distribution

Testability

• Mock provider for unit tests
• Fake MCP server/client
• Fake terminal/PTY
• Sandbox simulator
• Deterministic event replay

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7. Milestones

M0 — Foundation (Weeks 1-2)

• Go module setup
• Agent core skeleton
• 8 core tools (read, write, edit, bash, grep, glob, apply_patch, update_plan)
• OpenAI-compatible provider
• Basic Bubble Tea TUI
• Permission gate (read vs mutate)
• Session persistence

Exit: zero runs, can read/edit files, basic chat works.

M1 — Multi-Provider (Weeks 3-4)

• Anthropic provider
• Gemini provider
• Model registry
• Per-task model selection
• Provider rotation
• Cost tracking
• Headless exec mode

Exit: Switch between Claude/GPT/Gemini, see cost, run headless.

M2 — Polish (Weeks 5-8)

• Advanced TUI features
• Full markdown + syntax highlighting
• Tool result truncation/pagination
• Auto-compaction
• Context budgeting
• 20 slash commands
• Doctor command
• Search command

Exit: Production-ready TUI, smooth streaming, all commands work.

M3 — Distribution (Weeks 9-10)

• Single binary build
• Self-update
• Cross-platform CI
• VS Code extension MVP
• Documentation site

Exit: zero ships as one binary, works on Win/Mac/Linux.

M4 — Extensibility (Weeks 11-14)

• MCP client + permissions
• Hooks system
• Skills system
• Memory (AGENTS.md)
• Plugin loading
• Subagents (built-in: review, security)

Exit: Plugins work, MCP servers connect, memory persists.

M5 — Advanced (Weeks 15-20)

• Web fetch/search
• Git worktrees
• Self-verification
• Diagnostics (LSP, typecheck)
• Testing integration
• Code review automation

Exit: Zero can review code, run tests, manage git.

M6 — Sandbox & Security (Weeks 21-24)

• Linux sandbox (bubblewrap)
• macOS sandbox
• Windows AppContainer
• Network policies
• Filesystem policies

Exit: Untrusted code runs safely in sandbox.

Beyond v1.0

• Multi-modal (images, PDFs)
• Voice input
• Cloud sync (optional)
• Team features
• Marketplace (if demand)

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8. Risks & Mitigations

#	Risk	Mitigation
R1	Scope creep	Stick to milestones, defer features
R2	Provider API changes	Abstract via interface, test with mocks
R3	TUI complexity	Use Bubble Tea/Lip Gloss, follow mature terminal agent UX patterns
R4	Performance	Benchmark early, optimize streaming
R5	Security vulnerabilities	Permission gate from day 1, security review
R6	Cross-platform bugs	CI on Win/Mac/Linux from M0
R7	Breaking changes	Schema versioning, migration tools

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9. Success Metrics

v1.0 (6 months)

• 5+ providers supported
• 12+ tools
• 100% test coverage on core
• < 300ms cold start
• Single binary < 50MB
• Works on Win/Mac/Linux
• 1000+ GitHub stars
• 50+ contributors

v2.0 (12 months)

• VS Code extension published
• MCP server mode
• Plugin ecosystem (20+ plugins)
• 10K+ active users
• Compete with Claude Code on benchmarks

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10. Out of Scope (v1.0)

• Cloud sync / hosted backend
• Relay / remote SSH execution
• Multi-agent mission mode
• Plugin marketplace
• Auto-generated wikis
• Git authorship notes
• Vendor telemetry
• Voice input
• Mobile support

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11. Open Decisions

1. TUI library: Bubble Tea + Lip Gloss — Decide: Go-native TUI (single-binary friendly, mature terminal ecosystem)
2. Storage: JSONL files vs SQLite — Decide: JSONL (inspectable, simple)
3. Package structure: Single vs monorepo — Decide: Single until M4
4. Provider abstraction: Direct API vs wrapper — Decide: Direct (portability)
5. Patch strategy: apply_patch vs edit_file — Decide: Both (apply_patch for bulk, edit_file for small)

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12. Team & Timeline

Team (3 people):

• You (lead + TUI + tools)
• Backend dev (providers + core)
• Designer (VS Code extension + docs)

Timeline:

• M0-M1: 4 weeks (foundation)
• M2-M3: 6 weeks (polish + distribution)
• M4-M5: 8 weeks (extensibility)
• M6: 4 weeks (sandbox)
• Total v1.0: 6 months

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13. Why This Will Work

1. Proven patterns — Based on clean-room analysis of existing terminal coding-agent UX patterns
2. Multi-provider — Unique advantage vs Claude Code/Cursor
3. Open source — Community contributions
4. Go — Native binary, fast startup, strong concurrency, cross-platform CLI ergonomics
5. npm distribution wrapper — Keeps JavaScript ecosystem installation while the runtime stays native
6. Clear milestones — Ship early, iterate

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This is the real PRD. 13 sections, 24 features, 6 months to v1.0.