---
description: "Single Responsibility Principle applied to _docs/ artifacts. Each canonical file owns ONE concern and MUST NOT bleed into a sibling artifact's concern."
alwaysApply: true
---

# Artifact Single Responsibility

SRP is not only for code. Every canonical `_docs/` artifact owns exactly **one** concern. Mixing concerns across artifacts is a violation — fix the artifact, do not let the leak survive.

## Canonical artifact responsibilities

| Artifact | Owns ONLY | MUST NOT contain |
|---|---|---|
| `_docs/00_problem/problem.md` | What the system is for, the problem it solves, who uses it, the operational/environmental reality that defines the problem space. WHO + WHAT + WHY. | Technology choices, frameworks, languages, libraries, state-machine designs, component lists, internal data flows, IPC mechanisms, algorithms, schema names, "uses X library", "implements Y pattern". |
| `_docs/00_problem/restrictions.md` | Externally imposed constraints the system MUST satisfy: hardware (the device that already exists), regulatory, operational (deployment environment, climate, link reliability), vendor-fixed protocols (a chosen camera or radio whose protocol cannot be changed), legal/budget/timeline. | Design choices framed as constraints. "We chose Rust for memory safety" is design, not restriction. "The Jetson Orin Nano has 8 GB RAM" is a restriction. |
| `_docs/00_problem/acceptance_criteria.md` | Measurable, design-independent outcomes. What "done" looks like, expressed so a black-box test can verify it. | Implementation choices (libraries, params, algorithms, internal component names). AC is reverse-engineered FROM problem+restrictions, never FROM solution. |
| `_docs/00_problem/input_data/` | Reference data the system consumes + the input→quantifiable-expected-output mapping consumed by `/test-spec`. | Solution design or AC restatement. |
| `_docs/00_problem/security_approach.md` | Threat model + non-negotiable security principles + open security decisions. | Specific algorithms / libraries unless the AC truly mandates them (e.g. "must use AES-256" only if regulation forces it). |
| `_docs/01_solution/solution.md` | The chosen solution shape: high-level approach, the component breakdown name list, the tech stack with one-line rationale, pointers to the architecture deep dive. | Detailed flows (those belong in system-flows.md). Per-component contracts (those belong in component specs). Re-statement of the problem (point to it, do not duplicate). |
| `_docs/02_document/architecture.md` | System context, component layering, NFR targets, detailed design, MAVLink command surface, sync protocols, open architecture questions, scope boundary. The "how" at a system level. | Wholesale re-statement of problem.md, restrictions.md, AC, or solution overview. May briefly reference them; must not duplicate them. (If the project predates this rule and architecture.md has §Problem / §Restrictions / §AC sections, leave them but mark them as "MOVED to canonical location — keep this in sync or delete on next refactor".) |
| `_docs/02_document/system-flows.md` | Per-flow narratives + sequence diagrams. Behaviour over time. | Component implementation details (those live in component specs). |
| `_docs/02_document/data_model.md` | Canonical entity catalogue. | Component implementation details. |
| `_docs/02_document/components/<name>/description.md` | Per-component: purpose, inputs, outputs, responsibilities, state, failure modes, NFR targets, dependencies. | Cross-component flows (those live in system-flows.md). |
| `_docs/02_document/decision-rationale.md` | The "why" behind every load-bearing decision. Research evidence, reasoning chain, fact cards, fit matrix, validation log. | Authoritative architecture (point to architecture.md). |
| `_docs/02_document/glossary.md` | Project-specific terms only. | Generic CS/industry terms (RTSP, gRPC, JSON, etc.). |

## Litmus test (apply before writing or editing any of the above)

Before you save a file, scan each sentence and ask: **does this sentence belong to this artifact's concern (per the table above)?** If it belongs to a sibling artifact, move it there. Do not "summarise the system architecture in problem.md so the reader has context" — that is exactly the violation this rule exists to prevent.

Specific signals that you are leaking:

- problem.md mentions a programming language, framework, library, IPC mechanism, state-machine pattern, container, file format, RPC framework, or algorithm → solution leakage. Remove.
- restrictions.md says "we will use X because Y" or "the solution must be implemented with Z" → design choice masquerading as restriction. Move to solution.md (or architecture.md if it is a design non-negotiable).
- acceptance_criteria.md names a specific library, model file, or component → implementation leakage. Re-express as observable behaviour ("system returns N detections within Tms"), not "library X must return N detections".
- solution.md re-explains the problem in detail (more than a one-paragraph context-setter) → duplication. Point to problem.md instead.
- architecture.md restates AC numerically instead of referencing acceptance_criteria.md → duplication that will drift.

## When a fact is genuinely cross-cutting

Sometimes a single fact touches multiple concerns. Pick the artifact whose concern is *primary* and reference from the others:

- "ViewPro A40 is the camera." Hardware reality → **restrictions.md**. solution.md / architecture.md reference it.
- "Tier-1 inference lives in `../detections`, not in autopilot." Architectural non-negotiable → **architecture.md §5**. solution.md mentions it; restrictions.md does NOT (it is not an external constraint, it is a chosen split).
- "Operator commands must be authenticated, signed, replay-protected." This is a **principle / restriction** the threat model imposes → security_approach.md owns the principle; architecture.md owns the chosen scheme.
- "≤5 POIs / minute" is a **product requirement** → acceptance_criteria.md owns it; architecture.md owns how scan_controller enforces it.

## When you are tempted to skip the rule

Common excuses and the answer:

- "But the architecture document was authored before the canonical problem/solution split existed." → Then the architecture document over-reaches into other concerns. Mark the over-reaching sections "MOVED — see <canonical path>" and shrink them on the next refactor. Do not propagate the over-reach into newly authored artifacts.
- "But the reader needs context to understand the problem statement." → Context for the *problem* means **operational + environmental + user reality** (e.g. "the UAV flies at 600–1000 m, must work in winter snow"). Context does NOT mean a tour of the solution design.
- "But everyone will read both files anyway." → Then the duplication is harmless? No — duplication drifts. The two copies diverge silently and a reader cannot tell which one is authoritative.
- "But the source paragraph in architecture.md said it this way." → architecture.md may itself be in violation (see "When a project predates this rule" in the table above). Do not propagate a pre-existing violation when authoring a new file.

## Enforcement

- Any `/autodev` or skill workflow that writes one of the canonical artifacts MUST self-check against the table above before saving.
- When auditing an existing artifact, flag any sentence that violates the table. If the violation is in a file you are editing for another reason, fix it inline (per the "adjacent hygiene" allowance in coderule.mdc → "Scope discipline"). If it is in a file outside your current scope, record it in `_docs/_process_leftovers/` for later cleanup.