diff --git a/gitnexus/src/core/ingestion/scope-resolution/pipeline/reconcile-ownership.ts b/gitnexus/src/core/ingestion/scope-resolution/pipeline/reconcile-ownership.ts
new file mode 100644
index 000000000..5c0962848
--- /dev/null
+++ b/gitnexus/src/core/ingestion/scope-resolution/pipeline/reconcile-ownership.ts
@@ -0,0 +1,147 @@
+/**
+ * Reconcile scope-resolution's ownership view into the SemanticModel.
+ *
+ * For migrated languages (Python in particular) the legacy `parse` phase
+ * emits class-body callables without `ownerId` because
+ * `parsing-processor`'s `resolveEnclosingOwner` is language-dependent and
+ * not every extractor carries the enclosing-class info at parse time.
+ * Scope-resolution later calls `provider.populateOwners(parsed)`, which
+ * stamps the correct `ownerId` onto `parsed.localDefs[i]`. This pass
+ * mirrors those corrections into `model.methods` and `model.fields` so
+ * downstream passes can consult `SemanticModel` as the single
+ * authoritative owner-keyed index — no parallel scope-resolution
+ * registry is needed.
+ *
+ * ## Single-source-of-truth invariant (I9)
+ *
+ * After this pass runs, every `def in parsed.localDefs` with a non-
+ * undefined `ownerId` is reachable via either:
+ *   - `model.methods.lookupAllByOwner(ownerId, simpleName)` — if the
+ *     def is a Method / Function / Constructor, OR
+ *   - `model.fields.lookupFieldByOwner(ownerId, simpleName)` — if the
+ *     def is a Property / Variable.
+ *
+ * This invariant is the foundation of Contract Invariant I9
+ * (`contract/scope-resolver.ts`): scope-resolution passes MUST read
+ * symbol-keyed lookups exclusively from `SemanticModel`.
+ *
+ * ## Idempotency
+ *
+ * The pass skips registration when `(ownerId, simpleName)` already
+ * contains a def with matching `nodeId`. Safe to call multiple times
+ * or after a language whose legacy extractor does populate `ownerId`
+ * (C#) — no duplicates are introduced.
+ *
+ * ## Transitional shim
+ *
+ * This reconciliation pass is an explicit shim. The architectural end
+ * state is for the legacy extractor to emit the correct `ownerId` for
+ * every language at parse time, removing the need for a second pass.
+ * See ARCHITECTURE.md § "Semantic-model source of truth" for the
+ * follow-up plan.
+ */
+
+import type { ParsedFile } from 'gitnexus-shared';
+import type { MutableSemanticModel, SemanticModel } from '../../model/semantic-model.js';
+import { simpleQualifiedName } from '../graph-bridge/ids.js';
+
+export interface ReconcileStats {
+  /** Method/Function/Constructor defs registered into MethodRegistry. */
+  readonly methodsRegistered: number;
+  /** Property/Variable defs registered into FieldRegistry. */
+  readonly fieldsRegistered: number;
+  /** Defs already present (idempotent skip). */
+  readonly skippedAlreadyPresent: number;
+}
+
+export function reconcileOwnership(
+  parsedFiles: readonly ParsedFile[],
+  model: MutableSemanticModel,
+): ReconcileStats {
+  let methodsRegistered = 0;
+  let fieldsRegistered = 0;
+  let skippedAlreadyPresent = 0;
+
+  for (const parsed of parsedFiles) {
+    for (const def of parsed.localDefs) {
+      const ownerId = (def as { ownerId?: string }).ownerId;
+      if (ownerId === undefined) continue;
+      const simple = simpleQualifiedName(def);
+      if (simple === undefined) continue;
+
+      if (def.type === 'Method' || def.type === 'Function' || def.type === 'Constructor') {
+        const existing = model.methods.lookupAllByOwner(ownerId, simple);
+        if (existing.some((e) => e.nodeId === def.nodeId)) {
+          skippedAlreadyPresent++;
+          continue;
+        }
+        model.methods.register(ownerId, simple, def);
+        methodsRegistered++;
+      } else if (def.type === 'Property' || def.type === 'Variable') {
+        const existing = model.fields.lookupFieldByOwner(ownerId, simple);
+        if (existing !== undefined && existing.nodeId === def.nodeId) {
+          skippedAlreadyPresent++;
+          continue;
+        }
+        model.fields.register(ownerId, simple, def);
+        fieldsRegistered++;
+      }
+    }
+  }
+
+  return { methodsRegistered, fieldsRegistered, skippedAlreadyPresent };
+}
+
+/**
+ * Debug-mode parity validator. Runs only when
+ * `VALIDATE_SEMANTIC_MODEL !== '0'` AND `NODE_ENV !== 'production'`.
+ *
+ * Iterates every def in `parsedFiles[i].localDefs` with an `ownerId`
+ * and asserts it is reachable via `model.methods.lookupAllByOwner` or
+ * `model.fields.lookupFieldByOwner`. On mismatch: emits a warning via
+ * `onWarn` — never throws, mirroring the pipeline's soft-fail posture.
+ *
+ * This is the enforcement of Contract Invariant I9 at runtime. In
+ * production it is a no-op; in development it surfaces drift between
+ * `parsed.localDefs` and `SemanticModel` that would otherwise silently
+ * produce wrong edges.
+ */
+export function validateOwnershipParity(
+  parsedFiles: readonly ParsedFile[],
+  model: SemanticModel,
+  onWarn: (message: string) => void,
+): number {
+  if (process.env.NODE_ENV === 'production') return 0;
+  if (process.env.VALIDATE_SEMANTIC_MODEL === '0') return 0;
+
+  let mismatches = 0;
+  for (const parsed of parsedFiles) {
+    for (const def of parsed.localDefs) {
+      const ownerId = (def as { ownerId?: string }).ownerId;
+      if (ownerId === undefined) continue;
+      const simple = simpleQualifiedName(def);
+      if (simple === undefined) continue;
+
+      if (def.type === 'Method' || def.type === 'Function' || def.type === 'Constructor') {
+        const found = model.methods.lookupAllByOwner(ownerId, simple);
+        if (!found.some((d) => d.nodeId === def.nodeId)) {
+          onWarn(
+            `semantic-model parity: ${def.type} ${def.nodeId} (${parsed.filePath}) ` +
+              `owned by ${ownerId} as "${simple}" not in MethodRegistry`,
+          );
+          mismatches++;
+        }
+      } else if (def.type === 'Property' || def.type === 'Variable') {
+        const found = model.fields.lookupFieldByOwner(ownerId, simple);
+        if (found === undefined || found.nodeId !== def.nodeId) {
+          onWarn(
+            `semantic-model parity: ${def.type} ${def.nodeId} (${parsed.filePath}) ` +
+              `owned by ${ownerId} as "${simple}" not in FieldRegistry`,
+          );
+          mismatches++;
+        }
+      }
+    }
+  }
+  return mismatches;
+}
diff --git a/gitnexus/src/core/ingestion/scope-resolution/pipeline/run.ts b/gitnexus/src/core/ingestion/scope-resolution/pipeline/run.ts
index 151f421fd..c548597c9 100644
--- a/gitnexus/src/core/ingestion/scope-resolution/pipeline/run.ts
+++ b/gitnexus/src/core/ingestion/scope-resolution/pipeline/run.ts
@@ -26,7 +26,7 @@
 import type { ParsedFile, RegistryProviders } from 'gitnexus-shared';
 import type { KnowledgeGraph } from '../../../graph/types.js';
 import type { MutableSemanticModel } from '../../model/semantic-model.js';
-import { simpleQualifiedName } from '../graph-bridge/ids.js';
+import { reconcileOwnership, validateOwnershipParity } from './reconcile-ownership.js';
 import { extractParsedFile } from '../../scope-extractor-bridge.js';
 import { finalizeScopeModel } from '../../finalize-orchestrator.js';
 import { resolveReferenceSites, type ResolveStats } from '../../resolve-references.js';
@@ -104,35 +104,11 @@ export function runScopeResolution(
   }
 
   // Reconcile scope-resolution's ownership view into the SemanticModel.
-  // For migrated languages (Python in particular) the legacy extractor
-  // emits class-body members without `ownerId` —
-  // `provider.populateOwners(parsed)` above stamps the correct ownerId
-  // on `parsed.localDefs[i]`. Without this pass those defs would be
-  // invisible to `model.methods.lookupMethodByOwner` /
-  // `model.fields.lookupFieldByOwner`, forcing scope-resolution to
-  // maintain a parallel owner-keyed index. The pass is idempotent: we
-  // skip defs already present under `(ownerId, simpleName)` by nodeId,
-  // so re-running it (or running after a language whose legacy
-  // extractor does populate ownerId, e.g. C#) doesn't introduce
-  // duplicates.
-  for (const parsed of parsedFiles) {
-    for (const def of parsed.localDefs) {
-      const ownerId = (def as { ownerId?: string }).ownerId;
-      if (ownerId === undefined) continue;
-      const simple = simpleQualifiedName(def);
-      if (simple === undefined) continue;
-
-      if (def.type === 'Method' || def.type === 'Function' || def.type === 'Constructor') {
-        const existing = input.model.methods.lookupAllByOwner(ownerId, simple);
-        if (existing.some((e) => e.nodeId === def.nodeId)) continue;
-        input.model.methods.register(ownerId, simple, def);
-      } else if (def.type === 'Property' || def.type === 'Variable') {
-        const existing = input.model.fields.lookupFieldByOwner(ownerId, simple);
-        if (existing !== undefined && existing.nodeId === def.nodeId) continue;
-        input.model.fields.register(ownerId, simple, def);
-      }
-    }
-  }
+  // See `reconcile-ownership.ts` for the full rationale (Contract
+  // Invariant I9). Debug-mode validator runs immediately after to
+  // catch drift between `parsed.localDefs` and the registries.
+  reconcileOwnership(parsedFiles, input.model);
+  validateOwnershipParity(parsedFiles, input.model, onWarn);
 
   if (parsedFiles.length === 0) {
     return {
diff --git a/gitnexus/test/unit/scope-resolution/reconcile-ownership.test.ts b/gitnexus/test/unit/scope-resolution/reconcile-ownership.test.ts
new file mode 100644
index 000000000..bc8cd5a71
--- /dev/null
+++ b/gitnexus/test/unit/scope-resolution/reconcile-ownership.test.ts
@@ -0,0 +1,297 @@
+/**
+ * Unit tests for the reconciliation pass and parity validator that
+ * bridge scope-resolution's post-`populateOwners` ownership view into
+ * `SemanticModel` (Contract Invariant I9).
+ *
+ * The reconciliation pass is the load-bearing shim that lets scope-
+ * resolution passes consume `SemanticModel` as the single authoritative
+ * owner-keyed index even when the legacy parse phase emitted class-body
+ * callables without `ownerId` (e.g. Python).
+ */
+
+import { describe, it, expect, vi, afterEach } from 'vitest';
+import type { ParsedFile, SymbolDefinition } from 'gitnexus-shared';
+import { createSemanticModel } from '../../../src/core/ingestion/model/semantic-model.js';
+import {
+  reconcileOwnership,
+  validateOwnershipParity,
+} from '../../../src/core/ingestion/scope-resolution/pipeline/reconcile-ownership.js';
+
+// ─── Fixture helpers ────────────────────────────────────────────────────────
+
+const mkFile = (filePath: string, localDefs: readonly SymbolDefinition[]): ParsedFile => ({
+  filePath,
+  moduleScope: `scope:${filePath}#module`,
+  scopes: [],
+  parsedImports: [],
+  localDefs,
+  referenceSites: [],
+});
+
+const mkMethod = (opts: {
+  nodeId: string;
+  filePath: string;
+  name: string;
+  ownerId?: string;
+  type?: 'Method' | 'Function' | 'Constructor';
+}): SymbolDefinition => ({
+  nodeId: opts.nodeId,
+  filePath: opts.filePath,
+  type: opts.type ?? 'Method',
+  qualifiedName: opts.ownerId ? `${opts.ownerId.replace('def:', '')}.${opts.name}` : opts.name,
+  ...(opts.ownerId !== undefined ? { ownerId: opts.ownerId } : {}),
+});
+
+const mkProperty = (opts: {
+  nodeId: string;
+  filePath: string;
+  name: string;
+  ownerId: string;
+  type?: 'Property' | 'Variable';
+}): SymbolDefinition => ({
+  nodeId: opts.nodeId,
+  filePath: opts.filePath,
+  type: opts.type ?? 'Property',
+  qualifiedName: `${opts.ownerId.replace('def:', '')}.${opts.name}`,
+  ownerId: opts.ownerId,
+});
+
+// ─── reconcileOwnership ────────────────────────────────────────────────────
+
+describe('reconcileOwnership', () => {
+  it('registers a method with ownerId that the legacy extractor missed', () => {
+    const model = createSemanticModel();
+    const save = mkMethod({
+      nodeId: 'def:User.save',
+      filePath: 'models.py',
+      name: 'save',
+      ownerId: 'def:User',
+    });
+    const file = mkFile('models.py', [save]);
+
+    const stats = reconcileOwnership([file], model);
+
+    expect(stats.methodsRegistered).toBe(1);
+    expect(stats.fieldsRegistered).toBe(0);
+    expect(stats.skippedAlreadyPresent).toBe(0);
+    expect(model.methods.lookupAllByOwner('def:User', 'save')).toHaveLength(1);
+    expect(model.methods.lookupAllByOwner('def:User', 'save')[0]).toBe(save);
+  });
+
+  it('registers a property under FieldRegistry', () => {
+    const model = createSemanticModel();
+    const nameProp = mkProperty({
+      nodeId: 'def:User.name',
+      filePath: 'models.py',
+      name: 'name',
+      ownerId: 'def:User',
+    });
+    const file = mkFile('models.py', [nameProp]);
+
+    const stats = reconcileOwnership([file], model);
+
+    expect(stats.fieldsRegistered).toBe(1);
+    expect(stats.methodsRegistered).toBe(0);
+    expect(model.fields.lookupFieldByOwner('def:User', 'name')).toBe(nameProp);
+  });
+
+  it('registers a Variable type as a field (Python class-body assignments)', () => {
+    const model = createSemanticModel();
+    const attr = mkProperty({
+      nodeId: 'def:User.tag',
+      filePath: 'models.py',
+      name: 'tag',
+      ownerId: 'def:User',
+      type: 'Variable',
+    });
+    const file = mkFile('models.py', [attr]);
+
+    reconcileOwnership([file], model);
+
+    expect(model.fields.lookupFieldByOwner('def:User', 'tag')).toBe(attr);
+  });
+
+  it('skips defs without ownerId (top-level functions)', () => {
+    const model = createSemanticModel();
+    const topLevel = mkMethod({
+      nodeId: 'def:helper',
+      filePath: 'utils.py',
+      name: 'helper',
+      type: 'Function',
+    });
+    const file = mkFile('utils.py', [topLevel]);
+
+    const stats = reconcileOwnership([file], model);
+
+    expect(stats.methodsRegistered).toBe(0);
+    expect(model.methods.lookupAllByOwner('def:something', 'helper')).toEqual([]);
+  });
+
+  it('is idempotent — re-running skips defs already registered', () => {
+    const model = createSemanticModel();
+    const save = mkMethod({
+      nodeId: 'def:User.save',
+      filePath: 'models.py',
+      name: 'save',
+      ownerId: 'def:User',
+    });
+    const file = mkFile('models.py', [save]);
+
+    const first = reconcileOwnership([file], model);
+    const second = reconcileOwnership([file], model);
+
+    expect(first.methodsRegistered).toBe(1);
+    expect(second.methodsRegistered).toBe(0);
+    expect(second.skippedAlreadyPresent).toBe(1);
+    // Registry still contains exactly one entry, not two.
+    expect(model.methods.lookupAllByOwner('def:User', 'save')).toHaveLength(1);
+  });
+
+  it('coexists with pre-registered defs (legacy extractor already set ownerId)', () => {
+    const model = createSemanticModel();
+    // Simulate the legacy path: register via SymbolTable.add, which
+    // fans out to MethodRegistry via the dispatch table.
+    const save = model.symbols.add('models.cs', 'save', 'def:User.save', 'Method', {
+      ownerId: 'def:User',
+      qualifiedName: 'User.save',
+    });
+    const file = mkFile('models.cs', [save]);
+
+    const stats = reconcileOwnership([file], model);
+
+    expect(stats.methodsRegistered).toBe(0);
+    expect(stats.skippedAlreadyPresent).toBe(1);
+    expect(model.methods.lookupAllByOwner('def:User', 'save')).toHaveLength(1);
+  });
+
+  it('registers multiple overloads under the same (owner, name)', () => {
+    const model = createSemanticModel();
+    const log1 = mkMethod({
+      nodeId: 'def:Logger.log#1',
+      filePath: 'log.cs',
+      name: 'log',
+      ownerId: 'def:Logger',
+    });
+    const log2 = mkMethod({
+      nodeId: 'def:Logger.log#2',
+      filePath: 'log.cs',
+      name: 'log',
+      ownerId: 'def:Logger',
+    });
+    const file = mkFile('log.cs', [log1, log2]);
+
+    reconcileOwnership([file], model);
+
+    const overloads = model.methods.lookupAllByOwner('def:Logger', 'log');
+    expect(overloads).toHaveLength(2);
+    expect(overloads.map((d) => d.nodeId).sort()).toEqual(['def:Logger.log#1', 'def:Logger.log#2']);
+  });
+});
+
+// ─── validateOwnershipParity ───────────────────────────────────────────────
+
+describe('validateOwnershipParity', () => {
+  const originalNodeEnv = process.env.NODE_ENV;
+  const originalGate = process.env.VALIDATE_SEMANTIC_MODEL;
+
+  afterEach(() => {
+    if (originalNodeEnv === undefined) delete process.env.NODE_ENV;
+    else process.env.NODE_ENV = originalNodeEnv;
+    if (originalGate === undefined) delete process.env.VALIDATE_SEMANTIC_MODEL;
+    else process.env.VALIDATE_SEMANTIC_MODEL = originalGate;
+  });
+
+  it('emits no warnings when reconciliation has populated all owner-keyed defs', () => {
+    process.env.NODE_ENV = 'development';
+    const model = createSemanticModel();
+    const save = mkMethod({
+      nodeId: 'def:User.save',
+      filePath: 'models.py',
+      name: 'save',
+      ownerId: 'def:User',
+    });
+    const file = mkFile('models.py', [save]);
+    reconcileOwnership([file], model);
+
+    const onWarn = vi.fn();
+    const mismatches = validateOwnershipParity([file], model, onWarn);
+
+    expect(mismatches).toBe(0);
+    expect(onWarn).not.toHaveBeenCalled();
+  });
+
+  it('warns when a def with ownerId is not registered in the model', () => {
+    process.env.NODE_ENV = 'development';
+    const model = createSemanticModel();
+    const orphan = mkMethod({
+      nodeId: 'def:User.save',
+      filePath: 'models.py',
+      name: 'save',
+      ownerId: 'def:User',
+    });
+    const file = mkFile('models.py', [orphan]);
+    // Intentionally skip reconciliation to simulate the drift.
+
+    const onWarn = vi.fn();
+    const mismatches = validateOwnershipParity([file], model, onWarn);
+
+    expect(mismatches).toBe(1);
+    expect(onWarn).toHaveBeenCalledTimes(1);
+    expect(onWarn.mock.calls[0][0]).toMatch(/semantic-model parity/);
+    expect(onWarn.mock.calls[0][0]).toMatch(/MethodRegistry/);
+  });
+
+  it('is a no-op when NODE_ENV=production', () => {
+    process.env.NODE_ENV = 'production';
+    const model = createSemanticModel();
+    const orphan = mkMethod({
+      nodeId: 'def:User.save',
+      filePath: 'models.py',
+      name: 'save',
+      ownerId: 'def:User',
+    });
+    const file = mkFile('models.py', [orphan]);
+
+    const onWarn = vi.fn();
+    const mismatches = validateOwnershipParity([file], model, onWarn);
+
+    expect(mismatches).toBe(0);
+    expect(onWarn).not.toHaveBeenCalled();
+  });
+
+  it('is a no-op when VALIDATE_SEMANTIC_MODEL=0', () => {
+    process.env.NODE_ENV = 'development';
+    process.env.VALIDATE_SEMANTIC_MODEL = '0';
+    const model = createSemanticModel();
+    const orphan = mkMethod({
+      nodeId: 'def:User.save',
+      filePath: 'models.py',
+      name: 'save',
+      ownerId: 'def:User',
+    });
+    const file = mkFile('models.py', [orphan]);
+
+    const onWarn = vi.fn();
+    validateOwnershipParity([file], model, onWarn);
+
+    expect(onWarn).not.toHaveBeenCalled();
+  });
+
+  it('warns on missing Property just like missing Method', () => {
+    process.env.NODE_ENV = 'development';
+    const model = createSemanticModel();
+    const orphan = mkProperty({
+      nodeId: 'def:User.name',
+      filePath: 'models.py',
+      name: 'name',
+      ownerId: 'def:User',
+    });
+    const file = mkFile('models.py', [orphan]);
+
+    const onWarn = vi.fn();
+    const mismatches = validateOwnershipParity([file], model, onWarn);
+
+    expect(mismatches).toBe(1);
+    expect(onWarn.mock.calls[0][0]).toMatch(/FieldRegistry/);
+  });
+});