Archify Diagram Viewer 0.1.0

VS Code extension that previews Archify diagrams from their JSON sources
(live, as you type) and opens rendered Archify HTML in a viewer tab.
Bundles the Archify 3.0.1 renderer and runs it on VS Code's Node runtime.
Adds validation diagnostics, JSON schema help, source-link navigation,
export saving, render-to-file and open-in-browser commands.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

vendor/archify/renderers/sequence/README.md

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+# Sequence Renderer
+
+Render `diagram_type: "sequence"` JSON files into the standard Archify HTML
+template.
+
+```bash
+node archify/renderers/sequence/render-sequence.mjs input.sequence.json output.html
+```
+
+The renderer validates input against `archify/schemas/sequence.schema.json`
+with the bundled standalone validator. No dependency installation is required.
+
+If `output.html` is omitted, the renderer uses the required `meta.output` value
+from the JSON file.
+
+## Input
+
+Sequence JSON files must set:
+
+```json
+{
+  "schema_version": 1,
+  "diagram_type": "sequence",
+  "meta": {
+    "title": "Cache Miss Request Sequence",
+    "output": "cache-miss-request.html",
+    "viewBox": [920, 760]
+  },
+  "participants": [],
+  "segments": [],
+  "messages": [],
+  "activations": [],
+  "cards": []
+}
+```
+
+The timeline scales with the viewBox height: a taller `meta.viewBox` buys more
+message room, a shorter one shrinks the readable band instead of clipping. A
+complete worked example lives at
+`archify/examples/cache-miss-request.sequence.json`.
+
+The schema lives at:
+
+```text
+archify/schemas/sequence.schema.json
+```
+
+## Legend
+
+The default visual legend derives kinds from `messages[].variant` (omitting
+`variant` means `default`). Supported `meta.legend.entries` keys, in stable
+order, are `emphasis`, `return`, `security`, `dashed`, and `default`. These are
+visual message keys, not Semantic Lens controls; label/visibility overrides do
+not create edge facts.
+
+The legend sits below all timeline content: the last message and its note,
+activation bars, and segment frames, with a 12px gap. Without `meta.viewBox`
+the canvas grows to keep that gap. With an authored `viewBox` that is too short,
+`showcase` fails with the exact height to set, and `standard` hides the implicit
+legend rather than drawing it over content. Lifelines stop above the legend.
+Message labels use their line's color; gray default and return lines keep the
+muted text color.
+
+## Layout budget
+
+| Constant | Value |
+|----------|-------|
+| viewBox | default `[920, 760]`, taller when late content needs legend room; schema minimum `[480, 480]` |
+| Participant boxes | `fixed` (default): 86×54 at y 72; `spread`: viewBox-relative width from 86px up to 190px |
+| Participant columns | `fixed`: centers at x = 62 + index×108; `spread`: columns distribute across the available viewBox width |
+| Participant count | the last box must end at or before width − 40; layouts that cannot fit fail closed |
+| Lifelines | from y 142 down to height − 65 (drawn to just above the legend); band must be ≥120px tall |
+| Message `y` range | `[160, height − 83]` |
+| Message spacing | ≥28px vertical between messages that share horizontal space |
+| Arrow span | ≥60px horizontal between the two participants |
+| Segments | y pixel ranges with `to > from`, inside `[72, lifeline bottom + 20]` |
+| Legend | last row baseline at height − 54; extra rows wrap upward and stay 12px below the timeline content |
+
+`segments[].from/to` and `activations[].from/to` are y pixel coordinates, not
+participant ids; activations also require `to > from`.
+
+### Column fit
+
+Sequence diagrams use `meta.column_fit: "fixed"` by default so existing
+documents keep their historical coordinates. Use `"spread"` when a wide
+viewBox would otherwise leave empty space on the right or when meaningful
+participant labels do not fit the fixed 86px boxes. Spread derives box width
+and column distance from the viewBox while preserving participant order,
+lifelines, and message semantics.
+
+The artifact checker reports `composition.sequenceColumnSpace` from the rendered
+participants, routes and text. A large unused right-hand region in a fixed layout
+can produce an `inspect-sequence-width` recommendation in `finalize`; it is advice,
+not a new warning or failure. See [Sequence width review](../../references/delivery-contract.md#sequence-width-review)
+for the bounded authoring repair and explicit-fixed/legacy preservation rules.
+
+## Design Rules
+
+- Put participants across the top, ordered by the story the reader should
+  follow.
+- Time moves downward.
+- Use `emphasis` for the main request path.
+- Use `security` for auth, consent, permission, and policy calls.
+- Use `return` for quiet response messages.
+- Use `dashed` for async trace, event, logging, and non-blocking work.
+- Use segments as light background guides; keep segment labels short.
+- Keep labels concise, but try `meta.column_fit: "spread"` before shortening a
+  meaningful participant label just to fit the fixed boxes.
+
+Schema violations exit non-zero with path-prefixed messages annotated with the
+element's id or label. The renderer additionally fails when it can detect
+layout problems, including missing participants, duplicate participant IDs,
+participant labels wider than their box, unknown message endpoints, messages
+outside the readable timeline, overly tight vertical spacing between messages
+that overlap horizontally, invalid segment or activation ranges, or
+participants that exceed the viewBox. The shared Clean Flow contract treats
+participant headers as semantic boxes while explicitly allowing messages to
+cross intermediate lifelines, activation bars, and segment frames. Text width is estimated CJK-aware:
+fullwidth glyphs count as two units.
+
+Set `meta.quality_profile` to `showcase` for polished delivery. Unrelated proper
+message X crossings then fail with `composition/proper-crossing`; default
+`standard` keeps them as artifact-receipt warnings. Messages may still cross
+intermediate lifelines. Collinear corridors remain outside the proper-X rule,
+but a separate gate warns in `standard` and fails in `showcase` when unrelated
+messages overlap for at least 8px. Shared semantic endpoints, point touches,
+and shorter overlaps remain valid. Showcase also rejects any route segment
+below 8px and any interior turn segment below 16px; ordinary 8–15px endpoint
+stubs remain valid.

vendor/archify/renderers/sequence/render-sequence.mjs

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+import path from 'node:path';
+import { fileURLToPath } from 'node:url';
+import { esc, renderDefinitions, renderSemanticSigil, textUnits } from '../shared/utils.mjs';
+import { animateAttr, focusEdgeAttrs, focusNodeAttrs, focusNodeTitle, loadDiagramWithBrandMarks, writeDiagram, svgAccessibleText, svgRootAttrs } from '../shared/cli.mjs';
+import { throwDiagnosticProblems } from '../shared/diagnostics.mjs';
+import { legendFootprint, measureLegend, resolveLegend, renderLegend as renderResolvedLegend } from '../shared/legend.mjs';
+import { componentFill, arrowClassMap, rectsOverlap, cleanFlowProblems, cleanCrossingProblems, cleanAmbiguousCorridorProblems, cleanBorderRunProblems, cleanRouteRhythmProblems, cleanLabelRouteClearanceProblems, cleanLabelCanvasContainmentProblems, routePointsValue, asArray, isFinitePoint, edgeLabelAccent } from '../shared/geometry.mjs';
+import { availableNodeTextWidth, fittedNodeFontSize, minimumNodeTextWidth } from '../shared/text-fit.mjs';
+import { brandLabelFitWidth, brandMetadataFor, brandTopRailProblem, renderBrandMark } from '../shared/brand-marks.mjs';
+import { translateMessage as i18nText } from '../shared/i18n.mjs';
+
+const participantTextFit = {
+  sublabelPreferred: 7,
+  sublabelMinimum: 6,
+};
+
+const __dirname = path.dirname(fileURLToPath(import.meta.url));
+const { diagram: sequence, template, outPath, sourceEvidence } = await loadDiagramWithBrandMarks({
+  rendererDir: __dirname,
+  diagramType: 'sequence',
+  defaultExample: 'cache-miss-request.sequence.json'
+});
+
+const LEGEND_CATALOG = [
+  { kind: 'emphasis', className: 'a-emphasis', marker: 'arrowhead-emphasis', strokeWidth: 1.8 },
+  { kind: 'return', className: 'a-default', marker: 'arrowhead', dash: '3,5' },
+  { kind: 'security', className: 'a-security', marker: 'arrowhead-security' },
+  { kind: 'dashed', className: 'a-dashed', marker: 'arrowhead-dashed' },
+  { kind: 'default', className: 'a-default', marker: 'arrowhead' },
+].map((entry) => ({
+  ...entry,
+  interactive: false,
+  swatchWidth: 34,
+  swatchGap: 9,
+  label: i18nText(sequence.meta.locale, `legend.sequence.${entry.kind}`),
+}));
+
+function legendEntries() {
+  const presentKinds = new Set(asArray(sequence.messages).map((message) => message.variant || 'default'));
+  return resolveLegend(sequence.meta?.legend, LEGEND_CATALOG, presentKinds);
+}
+
+// The legend sits below the timeline content: the last message and its note,
+// activation bars, and segment frames. Its block starts LEGEND_CONTENT_GAP
+// below that content; from the block top to the canvas bottom a one-row legend
+// needs LEGEND_BLOCK_HEIGHT (title glyphs, row, and the 54px baseline inset).
+const LEGEND_CONTENT_GAP = 12;
+const LEGEND_BLOCK_HEIGHT = 86;
+const contentBottom = Math.max(
+  0,
+  ...asArray(sequence.messages).map((message) => message.y + (message.note ? 22 : 6)),
+  ...asArray(sequence.activations).map((activation) => activation.to),
+  ...asArray(sequence.segments).map((segment) => segment.to),
+);
+function legendRequiredHeight(width) {
+  const entries = legendEntries();
+  if (!entries.length) return 0;
+  return Math.ceil(contentBottom + LEGEND_CONTENT_GAP + LEGEND_BLOCK_HEIGHT
+    + legendFootprint(entries, { width: width - 80 }).extraHeight);
+}
+// A renderer-sized canvas grows to keep the legend clear of late messages;
+// an authored viewBox is honored and validated below.
+const viewBox = sequence.meta?.viewBox || [920, Math.max(760, legendRequiredHeight(920))];
+// The timeline scales with viewBox height: a taller viewBox gains message room,
+// a shorter one shrinks the readable band (validated below) instead of clipping.
+// `column_fit: "spread"` widens the lanes with the viewBox instead of keeping
+// the fixed 108px gap, so a wide canvas gains column distance and label room
+// rather than dead space on the right. The default stays "fixed" so existing
+// diagrams keep their coordinates.
+const columnFit = sequence.meta?.column_fit === 'spread' ? 'spread' : 'fixed';
+const participantCount = Math.max(1, asArray(sequence.participants).length);
+const sideMargin = 62;
+const participantW = columnFit === 'spread'
+  ? Math.max(86, Math.min(190, Math.round((viewBox[0] - sideMargin * 2) / participantCount) - 24))
+  : 86;
+const colGap = columnFit === 'spread' && participantCount > 1
+  ? Math.max(108, (viewBox[0] - 40 - sideMargin - participantW) / (participantCount - 1))
+  : 108;
+
+// Showcase is the fast-authoring default; standard retains legacy label geometry.
+const readableMessages = sequence.meta?.quality_profile === 'showcase';
+const messageFontSize = readableMessages ? 11 : 9;
+const messageUnitWidth = readableMessages ? 6.6 : 5.2;
+const layout = {
+  topY: 72,
+  participantW,
+  // Keep a separate top rail for the 11px semantic sigil and 16px brand mark.
+  // Literal labels retain their fitted font size and full authored wording.
+  participantH: 60,
+  participantLabelY: 36,
+  participantSublabelY: 50,
+  lifelineTop: 142,
+  lifelineBottom: viewBox[1] - 65,
+  legendY: viewBox[1] - 54,
+  leftX: columnFit === 'spread' ? sideMargin + participantW / 2 : sideMargin,
+  colGap,
+  labelH: readableMessages ? 18 : 16
+};
+
+const participantBoxWidthNote = columnFit === 'spread'
+  ? `participant boxes are ${participantW}px for this viewBox width and ${participantCount} participants`
+  : `participant boxes are a fixed ${participantW}px unless meta.column_fit is "spread"`;
+
+const arrowClass = {
+  ...arrowClassMap,
+  return: ['a-default', 'arrowhead']
+};
+
+function participantX(index) {
+  return layout.leftX + index * layout.colGap;
+}
+
+const participants = new Map(asArray(sequence.participants).map((participant, index) => [
+  participant.id,
+  {
+    ...participant,
+    index,
+    cx: participantX(index),
+    x: participantX(index) - layout.participantW / 2,
+    y: layout.topY,
+    width: layout.participantW,
+    height: layout.participantH,
+    cy: layout.topY + layout.participantH / 2
+  }
+]));
+
+function messageGeometry(message) {
+  const from = participants.get(message.from);
+  const to = participants.get(message.to);
+  if (!from || !to || typeof message.y !== 'number') return null;
+  const direction = to.cx > from.cx ? 1 : -1;
+  const start = from.cx + direction * 7;
+  const end = to.cx - direction * 7;
+  return { start, end, center: (start + end) / 2 };
+}
+
+function messageLabelBox(message, relationIndex = null) {
+  const geometry = messageGeometry(message);
+  if (!geometry) return null;
+  const width = Math.max(34, textUnits(message.label) * messageUnitWidth + 12);
+  return {
+    relation: message,
+    relationIndex,
+    label: message.label,
+    x: geometry.center - width / 2,
+    y: message.y - 20,
+    width,
+    height: layout.labelH,
+  };
+}
+
+function messageRouteBox(message) {
+  const geometry = messageGeometry(message);
+  if (!geometry) return null;
+  return {
+    x: Math.min(geometry.start, geometry.end),
+    y: message.y - 2,
+    width: Math.abs(geometry.end - geometry.start),
+    height: 4,
+  };
+}
+
+function segmentLabelBox(segment) {
+  const labelW = Math.max(42, textUnits(segment.label) * 5.2 + 14);
+  const occupied = asArray(sequence.messages)
+    .flatMap((message) => [messageLabelBox(message), messageRouteBox(message)])
+    .filter(Boolean);
+  const label = { x: 56, y: segment.from - 22, width: labelW, height: 18 };
+  for (let attempt = 0; attempt < 4; attempt += 1) {
+    if (!occupied.some((rect) => rectsOverlap(label, rect, 2))) break;
+    label.y -= 22;
+  }
+  return label;
+}
+
+const compositionFrames = asArray(sequence.segments).map((segment, index) => ({
+  id: index,
+  label: segment.label,
+  kind: 'segment',
+  x: 48,
+  y: segment.from,
+  width: viewBox[0] - 96,
+  height: segment.to - segment.from,
+  radius: 10,
+}));
+
+function messagePath(message) {
+  return {
+    points: participants.has(message.from) && participants.has(message.to)
+      ? [[participants.get(message.from).cx, message.y], [participants.get(message.to).cx, message.y]]
+      : []
+  };
+}
+
+function validateSequence() {
+  const problems = [];
+  if (participants.size !== asArray(sequence.participants).length) problems.push('Participant ids must be unique.');
+
+  if (layout.lifelineBottom - layout.lifelineTop < 120) {
+    problems.push(`viewBox height ${viewBox[1]} leaves under 120px of timeline — set meta.viewBox[1] to at least ${layout.lifelineTop + 120 + 65}.`);
+  }
+
+  for (const participant of participants.values()) {
+    const estLabelW = textUnits(participant.label) * 6.8;
+    if (estLabelW > layout.participantW + 6) {
+      problems.push(`Label "${participant.label}" (~${Math.round(estLabelW)}px) is wider than the ${layout.participantW}px participant box — shorten it.`);
+    }
+    const brandRailProblem = brandTopRailProblem(participant, layout.participantW, 8, 'Participant');
+    if (brandRailProblem) problems.push(brandRailProblem);
+    // sublabel renders as a single unwrapped <text>; shrink-to-fit handles the
+    // ordinary case, this rejects what it cannot rescue.
+    if (participant.sublabel) {
+      const availableTextW = availableNodeTextWidth(layout.participantW);
+      const minimumW = minimumNodeTextWidth(participant.sublabel, participantTextFit.sublabelMinimum);
+      if (minimumW > availableTextW) {
+        problems.push(`Sublabel "${participant.sublabel}" needs ~${Math.ceil(minimumW)}px at the ${participantTextFit.sublabelMinimum}px legible minimum, but participant "${participant.id}" provides ${availableTextW}px — shorten the sublabel (${participantBoxWidthNote}).`);
+      }
+    }
+  }
+
+  for (const message of asArray(sequence.messages)) {
+    if (!participants.has(message.from)) problems.push(`Message "${message.label}" references unknown source "${message.from}".`);
+    if (!participants.has(message.to)) problems.push(`Message "${message.label}" references unknown target "${message.to}".`);
+    if (typeof message.y !== 'number') problems.push(`Message "${message.label}" must provide a numeric y.`);
+    if (message.y < layout.lifelineTop + 18 || message.y > layout.lifelineBottom - 18) {
+      problems.push(`Message "${message.label}" sits outside the readable timeline — keep y between ${layout.lifelineTop + 18} and ${layout.lifelineBottom - 18}.`);
+    }
+    if (participants.has(message.from) && participants.has(message.to)) {
+      const distance = Math.abs(participants.get(message.to).cx - participants.get(message.from).cx);
+      if (distance < 60) problems.push(`Message "${message.label}" spans ${Math.round(distance)}px (minimum 60px) — give its participants more column distance.`);
+    }
+  }
+
+  // Participant headers are opaque nodes. Lifelines, activation bars, and
+  // segment bands remain intentional pass-through geometry and are excluded.
+  problems.push(...cleanFlowProblems({
+    relations: sequence.messages,
+    obstacles: participants.values(),
+    pathFor: messagePath,
+    diagramType: 'sequence',
+    relationCollection: 'messages',
+    obstacleKind: 'participant header',
+    clearance: 0,
+    routeHint: 'move the message y below the participant headers or reorder participants'
+  }));
+  problems.push(...cleanCrossingProblems({
+    relations: sequence.messages,
+    endpointIds: new Set(participants.keys()),
+    pathFor: messagePath,
+    diagramType: 'sequence',
+    relationCollection: 'messages',
+    profile: sequence.meta?.quality_profile,
+    routeHint: 'separate the message y values; lifeline crossings remain allowed'
+  }));
+  problems.push(...cleanAmbiguousCorridorProblems({
+    relations: sequence.messages,
+    endpointIds: new Set(participants.keys()),
+    pathFor: messagePath,
+    diagramType: 'sequence',
+    relationCollection: 'messages',
+    profile: sequence.meta?.quality_profile,
+    routeHint: 'separate the message y values so unrelated messages do not visually merge'
+  }));
+  problems.push(...cleanBorderRunProblems({
+    relations: sequence.messages,
+    endpointIds: new Set(participants.keys()),
+    frames: compositionFrames,
+    pathFor: messagePath,
+    diagramType: 'sequence',
+    relationCollection: 'messages',
+    profile: sequence.meta?.quality_profile,
+    routeHint: 'move the message y so it crosses a segment boundary perpendicularly or stays clearly inside the segment'
+  }));
+  problems.push(...cleanRouteRhythmProblems({
+    relations: sequence.messages,
+    endpointIds: new Set(participants.keys()),
+    pathFor: messagePath,
+    diagramType: 'sequence',
+    relationCollection: 'messages',
+    profile: sequence.meta?.quality_profile,
+    routeHint: 'increase participant spacing or simplify message routing so every turn has room to read'
+  }));
+
+  // Vertical crowding only matters when the arrows share horizontal space;
+  // disjoint arrows may legitimately run in parallel rows.
+  const placed = asArray(sequence.messages)
+    .filter((m) => participants.has(m.from) && participants.has(m.to))
+    .map((m) => ({
+      label: m.label,
+      y: m.y,
+      x1: Math.min(participants.get(m.from).cx, participants.get(m.to).cx),
+      x2: Math.max(participants.get(m.from).cx, participants.get(m.to).cx)
+    }))
+    .sort((a, b) => a.y - b.y);
+  for (let i = 0; i < placed.length; i += 1) {
+    for (let j = i + 1; j < placed.length && placed[j].y - placed[i].y < 28; j += 1) {
+      if (placed[i].x1 < placed[j].x2 && placed[j].x1 < placed[i].x2) {
+        problems.push(`Messages "${placed[i].label}" and "${placed[j].label}" are less than 28px apart and share horizontal space — spread their y values.`);
+      }
+    }
+  }
+
+  // Label masks can extend well past the arrow span, so check the actual
+  // label rectangles too — tangent arrows with long labels still collide.
+  const labelRects = asArray(sequence.messages)
+    .map((m, messageIndex) => messageLabelBox(m, messageIndex))
+    .filter(Boolean);
+  for (let i = 0; i < labelRects.length; i += 1) {
+    for (let j = i + 1; j < labelRects.length; j += 1) {
+      if (rectsOverlap(labelRects[i], labelRects[j], -2)) {
+        problems.push(`Labels "${labelRects[i].label}" and "${labelRects[j].label}" overlap — spread their message y values or shorten the labels.`);
+      }
+    }
+  }
+  problems.push(...cleanLabelRouteClearanceProblems({
+    relations: sequence.messages,
+    labels: labelRects,
+    endpointIds: new Set(participants.keys()),
+    pathFor: messagePath,
+    diagramType: 'sequence',
+    relationCollection: 'messages',
+    profile: sequence.meta?.quality_profile,
+    routeHint: 'spread the message y values, shorten the label, or reorder participants so the adjacent route stays visible'
+  }));
+  problems.push(...cleanLabelCanvasContainmentProblems({
+    labels: labelRects,
+    viewBox,
+    diagramType: 'sequence',
+    relationCollection: 'messages',
+    profile: sequence.meta?.quality_profile,
+    routeHint: 'shorten the label, reorder participants, or enlarge meta.viewBox',
+  }));
+
+  for (const segment of asArray(sequence.segments)) {
+    if (segment.to <= segment.from) {
+      problems.push(`Segment "${segment.label}" has invalid y range (from ${segment.from} to ${segment.to}) — "to" must be greater than "from".`);
+    }
+    if (segment.from < layout.topY || segment.to > layout.lifelineBottom + 20) {
+      problems.push(`Segment "${segment.label}" extends outside the canvas — keep its y range between ${layout.topY} and ${layout.lifelineBottom + 20}.`);
+    }
+    const labelBox = segmentLabelBox(segment);
+    const availableWidth = Math.max(0, viewBox[0] - 48 - labelBox.x);
+    if (labelBox.x + labelBox.width > viewBox[0] - 48) {
+      const requiredWidth = Math.ceil(labelBox.x + labelBox.width + 48);
+      problems.push(`Segment "${segment.label}" label (~${Math.round(labelBox.width)}px) exceeds the segment frame's available width (${availableWidth}px) — shorten the label or increase meta.viewBox[0] to at least ${requiredWidth}.`);
+    }
+  }
+
+  for (const activation of asArray(sequence.activations)) {
+    if (!participants.has(activation.participant)) problems.push(`Activation references unknown participant "${activation.participant}".`);
+    if (activation.to <= activation.from) problems.push(`Activation for "${activation.participant}" has invalid time range — "to" must be greater than "from".`);
+  }
+
+  const lastParticipant = asArray(sequence.participants)[asArray(sequence.participants).length - 1];
+  if (lastParticipant && participants.get(lastParticipant.id).cx + layout.participantW / 2 > viewBox[0] - 40) {
+    const requiredWidth = Math.ceil(participants.get(lastParticipant.id).cx + layout.participantW / 2 + 40);
+    problems.push(`Participants exceed viewBox width — set meta.viewBox[0] to at least ${requiredWidth} or remove a participant.`);
+  }
+
+  // Showcase must not silently drop the implicit legend because late content
+  // leaves no room for it; give the exact canvas height instead.
+  const legendHeight = legendRequiredHeight(viewBox[0]);
+  if (sequence.meta?.quality_profile === 'showcase' && sequence.meta?.legend === undefined
+    && legendHeight > viewBox[1] && !measureLegend(legendEntries(), legendLayout())) {
+    problems.push(`Sequence content ends at y=${contentBottom}, leaving no room for the legend below it — set meta.viewBox[1] to at least ${legendHeight} or omit meta.viewBox so the canvas grows.`);
+  }
+
+  if (problems.length) {
+    throwDiagnosticProblems('Sequence layout validation failed', problems, {
+      subject: { diagramType: 'sequence' },
+    });
+  }
+}
+
+function renderParticipant(participant) {
+  const fill = componentFill[participant.type] || 'c-external';
+  const hasSub = participant.sublabel != null && participant.sublabel !== '';
+  const sub = hasSub
+    ? `\n          <text data-detail="context" x="${participant.cx}" y="${layout.topY + layout.participantSublabelY}" class="t-muted" font-size="${fittedNodeFontSize(participant.sublabel, layout.participantW, participantTextFit.sublabelPreferred, participantTextFit.sublabelMinimum)}" text-anchor="middle">${esc(participant.sublabel)}</text>`
+    : '';
+  const brand = renderBrandMark(participant, { x: participant.x + layout.participantW - 22, y: layout.topY + 6 });
+  const labelFontSize = fittedNodeFontSize(participant.label, brandLabelFitWidth(participant, layout.participantW), 11, 8);
+  const passport = {
+    kind: participant.type,
+    sublabel: participant.sublabel,
+    context: i18nText(sequence.meta.locale, 'node.context.sequence'),
+    ...brandMetadataFor(participant),
+  };
+  return `        <g ${focusNodeAttrs(participant.id, participant.label, passport, sequence.meta.locale)}>
+          ${focusNodeTitle(participant.label, passport)}
+          <rect x="${participant.x}" y="${layout.topY}" width="${layout.participantW}" height="${layout.participantH}" rx="6" class="c-mask"/>
+          <rect x="${participant.x}" y="${layout.topY}" width="${layout.participantW}" height="${layout.participantH}" rx="6" class="${fill}"${animateAttr(sequence.meta, 'node', participant.index)} stroke-width="1.5"/>
+          ${renderSemanticSigil(participant.type, { icon: participant.icon, x: participant.x + 6, y: layout.topY + 6 })}${brand ? `\n          ${brand}` : ''}
+          <text data-node-label=""${hasSub ? ' data-detail-anchor=""' : ''} x="${participant.cx}" y="${layout.topY + layout.participantLabelY}" class="t-primary" font-size="${labelFontSize}" font-weight="600" text-anchor="middle">${esc(participant.label)}</text>${sub}
+        </g>`;
+}
+
+// Lifelines never enter the legend band. The legend is placed below all
+// timeline content, so stopping above its title still reaches every message.
+function lifelineEnd() {
+  const legend = measureLegend(legendEntries(), legendLayout());
+  return legend?.titleY == null ? layout.lifelineBottom : Math.min(layout.lifelineBottom, legend.titleY - 22);
+}
+
+function renderLifeline(participant, end) {
+  return `        <path d="M ${participant.cx} ${layout.lifelineTop} L ${participant.cx} ${end}" class="a-default" stroke-width="0.8" stroke-dasharray="3,7"/>`;
+}
+
+function renderSegment(segment, index) {
+  return `        <rect data-graph-role="structural-frame" data-composition-frame-kind="segment" data-composition-frame-id="${index}" x="48" y="${segment.from}" width="${viewBox[0] - 96}" height="${segment.to - segment.from}" rx="10" class="c-lane" stroke-width="1"/>`;
+}
+
+function renderSegmentLabel(segment, index) {
+  const label = segmentLabelBox(segment);
+  return `        <g data-graph-role="segment-label" data-segment-id="${index}">
+          <rect x="${label.x}" y="${label.y}" width="${label.width}" height="${label.height}" rx="3" class="c-mask"/>
+          <text x="${label.x + 6}" y="${label.y + 13}" class="t-dim" font-size="9" font-weight="600">${esc(segment.label)}</text>
+        </g>`;
+}
+
+function renderActivation(activation) {
+  const participant = participants.get(activation.participant);
+  const fill = componentFill[activation.type] || componentFill[participant.type] || 'c-external';
+  const x = participant.cx - 5;
+  const height = activation.to - activation.from;
+  return `        <rect x="${x}" y="${activation.from}" width="10" height="${height}" rx="3" class="c-mask"/>
+        <rect x="${x}" y="${activation.from}" width="10" height="${height}" rx="3" class="${fill}" stroke-width="1"/>`;
+}
+
+function messageLabel(message, x1, x2) {
+  const box = messageLabelBox(message);
+  const center = box ? box.x + box.width / 2 : (x1 + x2) / 2;
+  const y = message.y - 10;
+  const labelW = box?.width || Math.max(34, textUnits(message.label) * messageUnitWidth + 12);
+  // A colored line gets a label in the same color, as in the legend swatches.
+  // Gray lines (default and return) keep the readable muted text color.
+  const accent = ['emphasis', 'security', 'dashed'].includes(message.variant) ? edgeLabelAccent(message.variant) : 't-muted';
+  return `        <g data-detail="context">
+          <rect x="${center - labelW / 2}" y="${y - 10}" width="${labelW}" height="${layout.labelH}" rx="3" class="c-mask"/>
+          <text x="${center}" y="${y}" class="${accent}" font-size="${messageFontSize}" text-anchor="middle">${esc(message.label)}</text>
+        </g>`;
+}
+
+function renderMessage(message, index) {
+  const { start, end } = messageGeometry(message);
+  const [cls, marker] = arrowClass[message.variant || 'default'] || arrowClass.default;
+  const strokeWidth = message.variant === 'emphasis' ? 1.8 : 1.4;
+  const dash = message.variant === 'return' ? ' stroke-dasharray="3,5"' : '';
+  const note = message.note
+    ? `\n        <text data-detail="fine" x="${Math.min(start, end) + 12}" y="${message.y + 18}" class="t-dim" font-size="7">${esc(message.note)}</text>`
+    : '';
+  return `        <g ${focusEdgeAttrs(message.from, message.to, message.label, index, message.id)}>
+          <path data-composition-edge-from="${esc(message.from)}" data-composition-edge-to="${esc(message.to)}"${message.id ? ` data-composition-edge-id="${esc(message.id)}"` : ''} data-composition-points="${routePointsValue([[start, message.y], [end, message.y]])}" d="M ${start} ${message.y} L ${end} ${message.y}" class="${cls}"${animateAttr(sequence.meta, 'edge', index)} stroke-width="${strokeWidth}"${dash} marker-end="url(#${marker})"/>
+${messageLabel(message, start, end)}${note}
+        </g>`;
+}
+
+
+function legendLayout() {
+  return {
+    x: 40,
+    baselineY: layout.legendY,
+    width: viewBox[0] - 80,
+    // The same content-based budget as legendRequiredHeight(): a wrapped
+    // legend may use any rows it needs as long as it stays below the content.
+    minTitleY: Math.max(layout.lifelineTop, contentBottom + LEGEND_CONTENT_GAP),
+    unfit: sequence.meta?.legend === undefined ? 'hide' : 'error',
+    diagramType: 'sequence',
+  };
+}
+
+function renderLegend() {
+  return renderResolvedLegend({
+    entries: legendEntries(),
+    locale: sequence.meta.locale,
+    layout: legendLayout(),
+    renderSwatch: (entry) => `<path d="M ${entry.x} ${entry.baseline - 3} L ${entry.x + 34} ${entry.baseline - 3}" class="${entry.className}" stroke-width="${entry.strokeWidth || 1.4}"${entry.dash ? ` stroke-dasharray="${entry.dash}"` : ''} marker-end="url(#${entry.marker})"/>`,
+  });
+}
+
+function renderSvg() {
+  const participantList = [...participants.values()];
+  // Same default-canvas contract as lifecycle: 920x760 is below the 1.55 wide
+  // ratio, so without intrinsic-height the desktop Reader can neither narrow
+  // nor scroll it and every default sequence fails the browser gate.
+  const readerFit = sequence.meta?.viewBox ? '' : ' data-reader-fit="intrinsic-height"';
+  return `      <svg viewBox="0 0 ${viewBox[0]} ${viewBox[1]}" data-sequence-column-fit="${columnFit}"${readerFit} ${svgRootAttrs(sequence.meta)}>
+${svgAccessibleText(sequence.meta, 'sequence')}
+${renderDefinitions()}
+
+        <!-- Background Grid -->
+        <rect width="100%" height="100%" fill="url(#grid)" />
+
+        <!-- Time Segments -->
+${asArray(sequence.segments).map(renderSegment).join('\n\n')}
+
+        <!-- Lifelines -->
+${participantList.map((participant) => renderLifeline(participant, lifelineEnd())).join('\n')}
+
+        <!-- Activations -->
+${asArray(sequence.activations).map(renderActivation).join('\n')}
+
+        <!-- Messages -->
+${asArray(sequence.messages).map(renderMessage).join('\n\n')}
+
+        <!-- Segment Labels -->
+${asArray(sequence.segments).map(renderSegmentLabel).join('\n')}
+
+        <!-- Participants -->
+${participantList.map(renderParticipant).join('\n\n')}
+
+        <!-- Legend -->
+${renderLegend()}
+      </svg>`;
+}
+
+validateSequence();
+writeDiagram({
+  outPath,
+  template,
+  diagramType: 'sequence',
+  meta: sequence.meta,
+  svg: renderSvg(),
+  cards: sequence.cards,
+  sourceEvidence,
+});