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+# GraphDiagnostic Flow Fields — Design Proposal
+
+**Status:** Proposal
+**Date:** 2026-06-26
+**Author:** Big Pickle
+**Affected package:** `@intent-framework/core`
+**Related docs:** `docs/proposals/Reachability-Diagnostics.md`
+
+---
+
+## Problem
+
+The `GraphDiagnostic` type (defined in `packages/core/src/graph.ts:7-13`) currently carries `nodeId` and `semanticNodeId` to identify which ask or act a diagnostic refers to. There is no way to associate a diagnostic with a specific flow.
+
+Future flow-scoped diagnostics — such as `flow-step-not-surfaced` and `orphaned-flow` (designed in `Reachability-Diagnostics.md:68-106`) — need to report *which flow* is affected, not just which node. Without flow fields, a consumer of `inspectScreen()` cannot group diagnostics by flow or display flow context to the author.
+
+---
+
+## Goal
+
+Design the smallest additive extension to `GraphDiagnostic` that enables flow-scoped diagnostics, without breaking existing consumers.
+
+---
+
+## Proposed API Shape
+
+### One new type: `FlowDiagnosticMeta`
+
+```ts
+export type FlowDiagnosticMeta = {
+  flowNodeId: string
+  flowSemanticNodeId?: string
+}
+```
+
+### Make `GraphDiagnostic` carry optional flow meta
+
+```ts
+export type GraphDiagnostic = {
+  severity: DiagnosticSeverity
+  code: string
+  message: string
+  nodeId?: string
+  semanticNodeId?: string
+  flow?: FlowDiagnosticMeta
+}
+```
+
+### Rationale for a nested `flow` object (vs top-level fields)
+
+- **Namespacing**: `flowNodeId` and `flowSemanticNodeId` are only meaningful together. A flat `flowNodeId` without `flowSemanticNodeId` is ambiguous; grouping them into an optional object makes the relationship explicit.
+- **Forward compatibility**: If later we add `flowStepIndex` or `flowStepNodeId`, they naturally live inside `flow` without polluting the top-level type.
+- **Backward compatibility**: The `flow` field is optional (`flow?: FlowDiagnosticMeta`). Existing consumers that destructure only `severity`, `code`, `message`, `nodeId`, `semanticNodeId` continue to work unchanged.
+- **Type narrowing**: A consumer checking `if (d.flow)` immediately has access to the complete flow context, rather than checking two separate optional fields.
+
+### Example diagnostic using the new shape
+
+```ts
+{
+  severity: "warning",
+  code: "flow-step-not-surfaced",
+  message: 'Flow "signup" step "Secret" is not included in any surface.',
+  nodeId: "ask_secret",
+  semanticNodeId: "ask:secret",
+  flow: {
+    flowNodeId: "flow_signup",
+    flowSemanticNodeId: "flow:signup"
+  }
+}
+```
+
+---
+
+## Alternative: Flat top-level fields
+
+The `Reachability-Diagnostics.md:186-203` proposal originally suggested:
+
+```ts
+export type GraphDiagnostic = {
+  severity: DiagnosticSeverity
+  code: string
+  message: string
+  nodeId?: string
+  semanticNodeId?: string
+  flowNodeId?: string
+  flowSemanticNodeId?: string // new — optional
+}
+```
+
+**Rejected** because:
+
+1. Two new optional top-level fields with no structural relationship to each other. A consumer must remember to check both and understand they covary.
+2. Adding more top-level optional fields increases cognitive overhead for consumers that ignore flow diagnostics entirely.
+
+---
+
+## Alternative: Overload `nodeId` to reference the flow
+
+```ts
+// For flow-scoped diagnostics:
+{
+  nodeId: "flow_signup",   // nodeId now refers to the flow
+  semanticNodeId: "flow:signup",
+  stepNodeId: "ask_secret" // the affected step
+}
+```
+
+**Rejected** because:
+
+1. Polymorphic `nodeId` breaks existing consumers that assume it always refers to an ask or act node.
+2. Introduces a new `stepNodeId` field anyway, so no net field reduction.
+3. Violates the principle of least surprise.
+
+---
+
+## Impact on Existing Code
+
+### Changes to `packages/core/src/graph.ts`
+
+- Add `FlowDiagnosticMeta` type (2 lines).
+- Change `GraphDiagnostic` to include `flow?: FlowDiagnosticMeta` (add 1 line).
+
+### No changes needed to
+
+- `computeDiagnostics()` — existing diagnostics do not set `flow`, so no existing logic needs updating.
+- `inspectScreen()` — the augmentation step (`diagnostics.map(...)`) already spreads each diagnostic; the `flow` field passes through transparently.
+- `InspectedScreen` — no change needed; its `diagnostics: GraphDiagnostic[]` field is generic.
+- Any existing consumer that reads `audited.code` — new field is optional and ignored by destructuring.
+
+### Public API surface impact
+
+`FlowDiagnosticMeta` and the amended `GraphDiagnostic` are exported from `packages/core/src/index.ts`. This is additive only — no existing exports are removed or renamed.
+
+---
+
+## Interaction with Future Diagnostics
+
+### `flow-step-not-surfaced` (planned)
+
+```ts
+{
+  severity: "warning",
+  code: "flow-step-not-surfaced",
+  message: 'Flow "onboarding" step "VerifyEmail" is not in any surface.',
+  nodeId: "act_verifyEmail",
+  semanticNodeId: "act:verify-email",
+  flow: {
+    flowNodeId: "flow_onboarding",
+    flowSemanticNodeId: "flow:onboarding"
+  }
+}
+```
+
+### `orphaned-flow` (planned)
+
+```ts
+{
+  severity: "warning",
+  code: "orphaned-flow",
+  message: 'Flow "legacy" has no surfaced steps.',
+  flow: {
+    flowNodeId: "flow_legacy",
+    flowSemanticNodeId: "flow:legacy"
+  }
+  // No nodeId — the diagnostic is about the flow itself, not a specific step node
+}
+```
+
+---
+
+## Migration
+
+No migration needed. The new field is optional and additive. Consumers that ignore `flow` continue to see all existing fields unchanged.
+
+---
+
+## Open Questions
+
+1. **Should `FlowDiagnosticMeta` be its own exported type or inline in `GraphDiagnostic`?** This proposal exports it separately for documentation value and reuse potential. Inline is simpler but loses the named type in API docs.
+2. **Should we add `stepIndex` to `FlowDiagnosticMeta` now?** Could be useful for `flow-step-order-gap`, but this proposal prefers to add fields only when a diagnostic needs them (YAGNI).
+
+---
+
+## Related
+
+- `packages/core/src/graph.ts:7-13` — current `GraphDiagnostic` type
+- `docs/proposals/Reachability-Diagnostics.md` — reachability diagnostics design (defines the diagnostics that will use these fields)
+- `packages/core/src/index.ts:4` — public export of `GraphDiagnostic`