Expand v2 with explicitly supported diagram families

[anandpant]

Goal

Expand Sketchi v2 beyond its currently supported flowchart and mindmap contracts without restoring the legacy generic fallback behavior.

Current state

• packages/diagram-core registers flowchart and mindmap as explicit typed diagram families.
• Each supported family has core validation, deterministic rendering, tests, and Storybook coverage.
• tools/sketchi-generators defines the intended extension path for new diagram families.
• The old schema advertising 23 types, with most silently falling back to a flowchart template, was deleted in feat: replace legacy app with Sketchi v2 #217.

Direction

Prioritize new diagram families from product demand and eval evidence. Each family should be a real contract with notation and layout semantics, not a display label over generic flowchart output.

Candidate sequence for grooming:

1. State/decision trees: close to the current graph pipeline while adding meaningful semantics.
2. Organization/tree diagrams: hierarchical layouts with family-specific constraints.
3. Sequence/swimlane diagrams: lane and ordering semantics.
4. ER/class/dataflow diagrams: specialized notation and richer node models.
5. Timeline, Gantt, network, matrix, and other specialized families only when justified by demand.

Definition of done for each family

• A typed intermediate representation and semantic validator in diagram-core.
• Deterministic layout and scene generation in diagram-renderer.
• Validated persisted Excalidraw output in diagram-excalidraw.
• Generation guidance and candidate parsing.
• Maintained scenarios and quality assertions.
• Unit/functional tests and Storybook coverage.
• No fallback to another diagram type when the requested contract is unsupported.

Acceptance criteria

• This issue is groomed into one issue per selected diagram family or coherent family group.
• Priority is based on product demand and implementation fit, not the deleted 23-type inventory.
• Every shipped family satisfies the complete contract above.
• Unsupported types fail explicitly and are not advertised.

Current touchpoints

• packages/diagram-core/src/diagram-types.ts
• packages/diagram-core/src/diagram-types/
• packages/diagram-renderer/src/
• packages/diagram-excalidraw/src/
• packages/diagram-generation/
• packages/diagram-scenarios/
• tools/sketchi-generators/src/generators/diagram-type/

Rewritten after the Sketchi v2 replacement in #217. The old 19-of-23 inventory and fallback template map no longer exist.

[anandpant]

Grooming update (2026-02-20): sequence is no longer the known broken case from #68.\n\nCurrent template map includes sequence as an explicit template (packages/backend/lib/templates/index.ts:13-18), and #113 closed #68.\n\nIssue is still valid for the remaining unimplemented diagram types, but description text should be treated as stale where it says sequence is broken.

[anandpant]

Triage 2026-07-23: still valid. packages/diagram/core/src/diagram-types.ts registers exactly ["flowchart", "mindmap"], so the expansion work is entirely undone. The extension mechanism (tools/sketchi-generators/src/generators/diagram-type/) and all referenced pipeline stages exist, just moved from packages/diagram-* to packages/diagram/*. Two updates for future groomers: new families should also account for the CLI dispatch in apps/cli/src/builder.ts, and sequence diagrams are being (re)introduced via #236, which can serve as the template for further families.

[anandpant]

Closing this speculative umbrella in favor of #280, which reflects the current state after native Code Mode sequence support landed in #277. #280 completes sequence across the canonical core/generation/CLI/scenario/Storybook path; additional families should get focused issues only when product demand or eval evidence selects them.