Skill: sequences

Draws the runtime view of an already-designed feature: for each critical flow it produces a Mermaid sequenceDiagram block — generic participants, happy path plus the error branches the spec demands — and writes them into docs/features/<slug>/sad.md §6. One flow at a time, user confirms each. The diagrams are the bridge between the static design (§5 building blocks) and the data layer: every persist/read step you draw becomes a hint for the indexes data-model will need.

Diagram labels + §6 prose follow artifact_language — but the existing sad.md's language wins over the setting; Mermaid keywords (sequenceDiagram, participant, alt/else/end) and participant names that name real modules stay English → ../_shared/artifact-language.md.

This skill keeps only its own machinery. Question phrasing is shared → ../_shared/ask-style.md. Flow count is driven by the spec, not a cap — every §4 user story / §5 acceptance criterion is covered (size may collapse detail, never coverage) → ../_shared/size-matrix.md. Each diagram is confirmed in prose, never as raw Mermaid → ../_shared/diagram-presentation.md; whether each flow is confirmed per-diagram or written-and-summarized follows the interview-depth setting → ../_shared/interview-depth.md.

Owner

Tech Lead (drives the runtime decomposition). The PM confirms that each drawn flow matches a real user story; a backend engineer flags persist steps that imply a new index.

Inputs

• <slug> — same feature slug used by every earlier stage.
• Gate (hard-refuse if missing): docs/features/<slug>/sad.md. The §5 building-block view names the participants; §6 is where flows are written. If sad.md is absent → STOP and point: «run design <slug> first — sequences are written into its §6».
• (Expected) sad.md frontmatter target_surfaces — picks the participant vocabulary (UI-driven flows for a UI surface). Absent or empty → warn («surfaces undeclared — re-run design, or proceeding as backend-service») and treat as [backend-service] (→ ../_shared/surfaces.md); never silently guess a UI surface.
• (Optional) docs/features/<slug>/ux-flows.md — when it exists, the UI-driven flows drawn here agree with it: the <ui> steps follow the same screen path, and a flow may reference the SCR-NN id in a note; a divergence between a §6 flow and a ux-flow is surfaced, never silently drawn over.
• Strongly expected: docs/features/<slug>/spec.md — §4 user stories tell you which flows exist; §5 acceptance criteria are the coverage floor — every AC must be shown by a flow, a branch, or an explicit non-runtime N/A (the step-7 coverage check). Present by this stage in the normal pipeline; if genuinely absent, fall back to §6/§5 of sad.md for the flow list and note that AC-coverage can't be verified.
• (Optional) docs/features/<slug>/.size — depth hint for detail (XS/S may collapse a flow's internal steps), never for coverage. Absent → default to M and say so loudly in the handoff — «size M (default — no .size; run /sdd:classify-size <slug>)».
• (Optional) .claude/sdd.local.md interview_depth (else medium) — governs only the diagram-confirmation UX (per-diagram prose+ask vs. write+summarize-and-proceed); sequences does not open its own depth question (it honors the setting, or a --depth= arg if passed).

Protocol

1. Gate. test -f docs/features/<slug>/sad.md → fail = refuse with the pointer above. Then read §5 (participants) and §6 (any flows already drawn — this skill is additive, never rewrite an existing block).
2. Pick the flows — spec-driven, no cap. List the flows from spec.md §4 user stories + §5 acceptance criteria (absent the spec, from §6 itself): one flow per critical user story / distinct runtime path. There is no fixed cap — draw as many flows as the user stories and ACs need (the old "3–5" cap silently under-covered). Then plan AC coverage: map every §5 AC to where it will be shown — a dedicated flow, an alt/else branch inside the relevant flow, or explicitly non-runtime (e.g. a middleware-enforced 401, a build-time check) with a one-line reason. Size only collapses detail (XS/S may show fewer internal steps per flow), never coverage. Confirm the flow list and the AC→flow map with one AskUserQuestion before drawing — phrasing per ../_shared/ask-style.md.
3. Map participants — generic only. For each flow, draw participants from a fixed generic vocabulary: <client>, <ui>, <service>, <data-store>, <external-system>, <message-bus>. Do not invent concrete service or technology names — those are design/data-model decisions, not runtime-view ones. When sad.md frontmatter target_surfaces declares a UI surface (web-frontend / mobile-app / desktop-app), draw the flows it touches as UI-driven — <user> (actor) → <ui> → <service> → <data-store> — so the user-visible step is shown, not just the service call (→ ../_shared/surfaces.md). A backend-only / cli / worker feature keeps the service-level vocabulary (no <ui>). <ui> stays generic, like every other participant — never a framework or component name. If a flow needs a participant §5 never declared, note it («flow needs <message-bus>, not in §5 — flag for design») and still draw it.
4. Sync vs async. If the spec describes a webhook, scheduled job, queued/event-driven step, or any third-party callback → async: add an idempotency-key check as the handler's first step, a retry note (Note over <service>,<external-system>: retry N times with backoff), and a dead-letter branch in an alt after N failures. Otherwise → sync (request → response).
5. Draft each flow from ./templates/sequence.md: a precondition note, the happy-path messages, an alt/else for the error branches the spec's acceptance criteria require, and a postcondition note. Mark every write as a generic persist note — Note over <service>,<data-store>: persists <entity> — so data-model sees what to index. Keep messages verb-first and free of HTTP verbs / status numbers / SQL.
6. Present + confirm each flow, one at a time — in prose, never raw Mermaid. Per ../_shared/diagram-presentation.md: for each drafted flow, write the block into §6 under a ### <flow name> heading (so Obsidian renders it), validate it parses per ../_shared/mermaid-check.md, then describe it in prose — the happy path plus every alt/else branch in plain words. Never paste the raw sequenceDiagram source as the question. Confirm by prose, governed by the interview-depth setting: at medium/hard, one AskUserQuestion per flow with the 4-state actions from ../_shared/ask-style.md (Accept / Fix / Save-as-OQ / Drop) — on Fix, regenerate + overwrite that one block, re-validate, re-describe (one round, second answer final); on Drop, remove the block again. At easy, write + a one-line prose summary into the assumptions ledger and proceed (no per-flow question). Never touch a flow already present in §6. Maintain the edits-log per ../_shared/socratic-loop.md.
7. Use-case + AC → flow coverage check (before finalizing). Two passes, surfaced as one coverage table:
   • Use-case pass (§4). List every §4 user story and the flow(s) that realize it. Every retained user story maps to ≥1 flow (a US with no flow is a gap — draft + confirm one, or de-scope it back through specify/clarify, never silently skip). specify already guarantees every §4 US carries ≥1 AC and clarify re-catches a US with none, so this pass is the runtime-view echo of that floor — both ends now checked, not just transitively assumed.
   • AC pass (§5). List every §5 AC and where it is now shown — a dedicated flow, an alt/else branch, or an explicit non-runtime N/A (with its one-line reason, e.g. «AC-7: middleware-enforced 401, not a runtime flow»). If a Drop/Save-as-OQ during step 6 left a user story or an AC uncovered, draft + confirm the missing flow or branch (the step 5–6 mini-loop) before proceeding, or record the explicit N/A with the user. No §4 user story and no §5 AC may be silently uncovered. (Completeness is independent of depth + size; this gate holds even at easy/XS.)
8. Finalize: order, validate, propose commit. Order the §6 blocks to match §4. Re-validate every sequenceDiagram block per ../_shared/mermaid-check.md as the backstop (balanced alt/else/end, declared participants; fix any that don't parse before committing). Append any flagged items (new participants, decisions worth an ADR) as a short note at the end of §6 — flag only, never auto-write an ADR. Propose commit sequences: <slug> runtime flows. Then emit the stage-handoff block per ../_shared/handoff.md — What I did + Review (sad.md §6) + Run next — resolve the next stage per .route (the Routes table in ../_shared/size-matrix.md): forward /sdd:data-model <slug> (which uses the persist notes to choose indexes); data-model's N/A condition = no schema change (no new entity/column/index in any drawn flow), skip target /sdd:api <slug> (on quick — auto-skip with the reason + inverted ↳ or; on standard — offer the ↳ or; on full — no skip line).

Definition of Done

• sad.md §6 holds a Mermaid sequenceDiagram for every critical user story / distinct runtime path — no fixed cap; size may collapse a flow's internal detail, never its coverage.
• Every §4 user story maps to ≥1 flow, and every §5 AC maps to a flow, an alt/else branch, or an explicit non-runtime N/A — the step-7 coverage check passed on both passes (use-case + AC); nothing is silently uncovered (holds at every depth + size).
• Each flow was confirmed in prose (medium/hard) or written + summarized (easy) — never by pasting raw sequenceDiagram source as the question.
• Every block uses only generic participants (<client> / <ui> / <service> / <data-store> / <external-system> / <message-bus>) — no concrete technology or service names. A declared UI surface uses <ui> in a UI-driven flow (<user> → <ui> → <service> → <data-store>); a backend-only feature omits it.
• Each flow shows the error branches its spec acceptance criteria require, not happy-path only; every mutating step carries a generic persist note for data-model.
• Every async flow has an idempotency-key step, a retry note, and a dead-letter branch.
• Pre-existing §6 blocks are untouched; new participants / ADR-worthy decisions are flagged, not silently added.
• The step-7 use-case + AC coverage check + the step-8 mermaid re-validation are this skill's structural self-check (../_shared/self-check.md); its result is reported in the handoff.

Anti-patterns

• Concrete participants. Postgres, content-api, a specific broker — the legacy trap. Participants stay generic; naming the tech is the job of design/data-model.
• Capping the flow count (the old "3–5") and silently under-covering. Flow count is driven by §4/§5 — every AC is shown by a flow, a branch, or an explicit N/A. A dogfood run that drew only 2 flows for a spec with 6 ACs is the exact failure this skill now forbids.
• Pasting raw Mermaid as the confirmation. sequenceDiagram source in the terminal is unreadable — the user approves blind. Confirm in prose; let Obsidian render the written block (per ../_shared/diagram-presentation.md).
• Happy path only when the spec lists explicit error acceptance criteria. Each flow gets happy + the demanded error branches.
• One mega-diagram for the whole feature. Split per flow; a cross-cutting flow gets its own ### Cross-cutting: <name> heading.
• Auto-writing ADRs. This skill only flags decisions (idempotency strategy, retry shape, sync-vs-async); ADRs come from decide-adr or a human.
• Rewriting an existing §6 block. Additive only — editing a drawn flow is a deliberate manual diff.
• Inventing a participant §5 never declared without flagging it. §5 is the source of truth; the flag lets design reconcile it.

References & template

• ../_shared/ask-style.md — canonical question/option phrasing for steps 2 and 6.
• ../_shared/diagram-presentation.md — how each flow is confirmed (write → validate → prose-describe → confirm/proceed); never raw Mermaid as the question.
• ../_shared/interview-depth.md — the depth setting that governs per-flow ask vs. write-and-summarize (read from settings; sequences asks no depth question of its own).
• ../_shared/mermaid-check.md — parse-validation run on each block at step 6 and again as the step-8 backstop.
• ../_shared/size-matrix.md — collapses a flow's detail for XS/S (never its coverage — every AC is still shown).
• ../_shared/surfaces.md — a declared UI surface adds <ui> to the vocabulary and draws UI-driven flows; read from sad.md target_surfaces.
• ./templates/sequence.md — generic-participant sequenceDiagram scaffold (sync + async), embedded inline in sad.md §6.