# AGENTS.md — Build guide for CodeSandbox ## Project scope Launch a developer-owned repository in one isolated container template, expose a preview and keep editor files on a persistent workspace volume. Catalogue verdict: kinda. You can self-host a browser IDE, but fast templates, previews, cloud VMs, collaboration, and workflow integrations are the product. Use the implementation prompt below to define the deliverable. Complete each phase's acceptance checks before extending the scope. ## Working agreement - Inspect the repository and its existing instructions before choosing paths, dependencies or commands. Keep one coherent stack and explain changes to the proposed architecture. - Plan a vertical slice that accepts a real input and produces the useful output described below. Persist only the state the prompt calls for; respect memory-only and upstream-managed workflows. Use fixtures only when they are clearly labelled. - After scaffolding, document the actual install, development, check and build commands in README and keep them synchronized with the package or project manifest. Do not report commands as successful unless they ran. - Work in small steps. At handoff, list implemented flows, checks actually performed, remaining blockers, and any credentials or provider setup the owner must supply. - Do not publish, spend money, contact customers, delete source data or run irreversible migrations without the project owner's authorization. ## Prerequisites - Runtime and tools: TypeScript, Node, PostgreSQL and a database-backed job worker with a small React run inspector. - Before starting: Credentials for only the chosen integrations, their current API documentation, example payloads and an always-on worker for schedules. ## Stack and architecture - TypeScript, Node, PostgreSQL and a database-backed job worker with a small React run inspector - Data design: Store Workspace, TemplateVersion, ContainerRun, PortGrant and Snapshot; an exited process does not delete source files, and only explicitly approved preview ports are exposed. - Setup: Credentials for only the chosen integrations, their current API documentation, example payloads and an always-on worker for schedules ## Security and data integrity - Persist trigger identity, step input version and external receipts before marking success. Retry bounded transient failures; unknown write outcomes require reconciliation. Do not promise exactly-once execution across external services. - This MVP is for one trusted developer, not hostile public code execution. No Docker socket inside workspaces; stronger tenant isolation and resource policy are prerequisites for public hosting. - Keep secrets outside client bundles and exported projects; document what leaves the device and make retention/deletion controls visible. ## Agent implementation rules - Project rule — domain: Store Workspace, TemplateVersion, ContainerRun, PortGrant and Snapshot; an exited process does not delete source files, and only explicitly approved preview ports are exposed. - Project rule — scope and recovery: This MVP is for one trusted developer, not hostile public code execution. No Docker socket inside workspaces; stronger tenant isolation and resource policy are prerequisites for public hosting. - Project rule — acceptance: Start a template that binds two ports, stop and restart it, then inspect the files; only the allowed preview is reachable and edits persist. - Project rule — delivery: document real setup commands and permissions; do not claim a build, accuracy level, performance result or security certification that has not been demonstrated. ## Optional agent skills and references - Recommended skill: [supabase-postgres-best-practices](https://github.com/supabase/agent-skills/blob/main/skills/supabase-postgres-best-practices/SKILL.md) — review this PostgreSQL domain schema, uniqueness constraints, transaction boundaries and access-scoped queries; Supabase hosting is not required. Follow the maintainer's installation instructions and match its requirements to the chosen runtime. - Recommended skill: [sharp-edges](https://github.com/trailofbits/skills/blob/main/plugins/sharp-edges/skills/sharp-edges/SKILL.md) — review configuration and API defaults against the app-specific invariants and recovery boundaries above; this is not a security certification. Follow the maintainer's installation instructions and match its requirements to the chosen runtime. Read the linked SKILL.md and its dependencies before adding a skill. Select only the skills matching this project's runtime and task; their documentation does not supply API access, credentials or approval to perform external actions. Pin the reviewed revision where the tool supports it. Follow the chosen agent's documented project-level installation mechanism. ## Distribution ideas These are optional planning notes. Obtain the owner's approval before publishing or contacting anyone. - Demonstrate this working slice using synthetic or explicitly authorized non-sensitive examples: Launch a developer-owned repository in one isolated container template, expose a preview and keep editor files on a persistent workspace volume. - Share a synthetic example export and the acceptance walkthrough; keep real customer, health, financial and source data private: Start a template that binds two ports, stop and restart it, then inspect the files; only the allowed preview is reachable and edits persist. - State the limits before asking someone to replace their existing tool: This MVP is for one trusted developer, not hostile public code execution. No Docker socket inside workspaces; stronger tenant isolation and resource policy are prerequisites for public hosting. ## Engineering roadmap 1. Phase 1 — Pin the working slice and create its example input: Launch a developer-owned repository in one isolated container template, expose a preview and keep editor files on a persistent workspace volume. Confirm setup: Credentials for only the chosen integrations, their current API documentation, example payloads and an always-on worker for schedules. 2. Phase 2 — Implement persistence and write-time invariants before decorating the UI: Store Workspace, TemplateVersion, ContainerRun, PortGrant and Snapshot; an exited process does not delete source files, and only explicitly approved preview ports are exposed. 3. Phase 3 — Connect the working view to real saved state. Persist trigger identity, step input version and external receipts before marking success. Retry bounded transient failures; unknown write outcomes require reconciliation. Do not promise exactly-once execution across external services. 4. Phase 4 — Expose the app-specific limits and recovery path in context: This MVP is for one trusted developer, not hostile public code execution. No Docker socket inside workspaces; stronger tenant isolation and resource policy are prerequisites for public hosting. 5. Phase 5 — Walk through this concrete acceptance case and preserve its exported evidence: Start a template that binds two ports, stop and restart it, then inspect the files; only the allowed preview is reachable and edits persist. Finish the README and backup/restore instructions; report unfinished capabilities explicitly. ## Paid-product capabilities outside this build - instant templates - cloud sandboxes - preview URLs - collaboration - managed infrastructure - integration polish ## Implementation prompt Build the following focused alternative to CodeSandbox. This is a deliberately limited personal or small-team substitute, not parity with the paid service. WORKING SLICE Launch a developer-owned repository in one isolated container template, expose a preview and keep editor files on a persistent workspace volume. SETUP AND ARCHITECTURE Use TypeScript, Node, PostgreSQL and a database-backed job worker with a small React run inspector. Prerequisites: Credentials for only the chosen integrations, their current API documentation, example payloads and an always-on worker for schedules. Before integrating anything, record actual versions and permissions, plus model files or provider limits only where used, in the README; make unavailable dependencies visible rather than simulating success. DOMAIN MODEL AND INVARIANTS Store Workspace, TemplateVersion, ContainerRun, PortGrant and Snapshot; an exited process does not delete source files, and only explicitly approved preview ports are exposed. IMPLEMENTATION CONTRACT Persist trigger identity, step input version and external receipts before marking success. Retry bounded transient failures; unknown write outcomes require reconciliation. Do not promise exactly-once execution across external services. Provide an input/setup view, the main work view, and a review/export view appropriate to this workflow. Preserve the last saved state if a job or save fails. Include empty, loading, permission-denied, partial and retryable-error states. Log identifiers and error categories without secret values or unnecessary private content. APP-SPECIFIC BOUNDARY AND RECOVERY This MVP is for one trusted developer, not hostile public code execution. No Docker socket inside workspaces; stronger tenant isolation and resource policy are prerequisites for public hosting. ACCEPTANCE SCENARIO Start a template that binds two ports, stop and restart it, then inspect the files; only the allowed preview is reachable and edits persist. Also reopen the app after an interrupted operation, confirm the saved record/export remains inspectable, and document the recovery action. These are implementation acceptance requirements, not a claim that this guide has been tested. DELIVERY Deliver a runnable repository with migrations or project-format versioning, a non-sensitive example, environment/permission setup, the exact manual acceptance steps, and a backup/export-and-restore walkthrough. Implement the working slice before optional integrations; list any deferred paid-product capabilities honestly. Do not add capabilities outside the working slice just to resemble the original product. PROJECT RULES FOR AGENTS.md Keep the domain invariants above executable at the write boundary. Propose scope changes before adding providers or permissions. Never fabricate source evidence, publish results, identity matches or successful delivery. Preserve user originals and require an explicit confirmation for destructive changes or external publication. ## Completion evidence Demonstrate the prompt's acceptance scenarios against the scoped workflow. Include setup from a clean checkout and failure recovery. Check persistence across restart and export/restore only for the state the prompt says to store; for memory-only tools, confirm that temporary content is discarded as specified. Record actual results and remaining limitations. A detailed plan alone does not establish a working replacement.