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guides/PRD.md

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+# PRD Requirement Guide (MANDATORY)
+
+This guide defines how requirements are captured before coding.
+
+## Hard Rules
+
+1. Before coding begins, `docs/PRD.md` or `docs/PRD.json` MUST exist.
+2. The PRD is the authoritative requirements source for implementation and testing.
+3. The main agent MUST prepare or update the PRD using user input and available project context before implementation starts.
+4. The agent MUST NOT invent requirements silently.
+5. In steered autonomy mode, best-guess decisions are REQUIRED when needed; each guessed decision MUST be marked with `ASSUMPTION:` and rationale.
+
+## PRD Format
+
+Allowed canonical formats:
+
+1. `docs/PRD.md`
+2. `docs/PRD.json`
+
+Either format is valid. Both may exist if one is a transformed representation of the other.
+For markdown PRDs, start from `~/.config/mosaic/templates/docs/PRD.md.template`.
+
+## Best-Guess Mode
+
+Steered autonomy is the default operating mode.
+
+1. Agent SHOULD fill missing decisions in the PRD without waiting for routine confirmation.
+2. Agent MUST mark each guessed decision with `ASSUMPTION:` and rationale.
+3. If user explicitly requests strict-confirmation mode, the agent MUST ask before unresolved decisions are finalized.
+4. For high-impact security/compliance/release uncertainty, escalate only if the decision cannot be safely constrained with rollback-ready defaults.
+
+## Minimum PRD Content
+
+Every PRD MUST include:
+
+1. Problem statement and objective
+2. In-scope and out-of-scope
+3. User/stakeholder requirements
+4. Functional requirements
+5. Non-functional requirements (security, performance, reliability, observability)
+6. Acceptance criteria
+7. Constraints and dependencies
+8. Risks and open questions
+9. Testing and verification expectations
+10. Delivery/milestone intent
+
+## Pre-Coding Gate
+
+Coding MUST NOT begin until:
+
+1. PRD file exists (`docs/PRD.md` or `docs/PRD.json`)
+2. PRD has required sections
+3. Unresolved decisions are captured as explicit `ASSUMPTION:` entries with rationale and planned validation
+
+## Change Control
+
+When requirements materially change:
+
+1. Update PRD first.
+2. Then update implementation plan/tasks.
+3. Then implement code changes.
+
+Implementation that diverges from PRD without PRD updates is a blocker.