diff --git a/TRACKER.md b/TRACKER.md
index e4b51be..b0faab3 100644
--- a/TRACKER.md
+++ b/TRACKER.md
@@ -5,8 +5,8 @@
 ## Status
 
 - **Current phase:** 2 — Instance graph & cross-file data flow
-- **Next step:** 2.3 — Handler resolution through props
-- **Done:** 0.1–0.4, 1.1–1.6, 2.1, 2.2 (headline: per-instance attribution green)
+- **Next step:** 2.4 — Store adapter: writers ↔ readers
+- **Done:** 0.1–0.4, 1.1–1.6, 2.1–2.3
 - **Gates passed:** Gate 0 (CI + red-path, PRs #5/#6) · Gate 1 (precision 1.000 ≥ 0.90, recall 0.895 ≥ 0.80 across C2/C3/C5/A2/A7/A8/D4, zero forbidden hits)
 
 ## What CodeRadar is
@@ -157,7 +157,7 @@ The heart of the project. C1 and B1 live here.
 - Depth limit (default 5 hops) with `flags: ["depth-limited"]` when hit.
 **Accept:** **c1-shared-datatable attribution assertions flip from expected-fail to green** — DataTable@Users → `/api/users`, DataTable@Invoices → `/api/invoices`, zero `forbidden` hits. Instance attribution accuracy = 1.0 on C1 fixtures.
 
-### [ ] 2.3 Handler resolution through props
+### [x] 2.3 Handler resolution through props
 **Failure modes:** B1
 **Build:** same machinery, callback direction:
 - `onClick={props.onSave}` → resolve `onSave` at each parent instance → the passed function → its body (which Phase 3 mines for effects). Chain recorded as evidence (`edge-chain`).
diff --git a/eval/fixtures/b1-prop-drilled-handler/app/DraftEditor.tsx b/eval/fixtures/b1-prop-drilled-handler/app/DraftEditor.tsx
new file mode 100644
index 0000000..dc9113a
--- /dev/null
+++ b/eval/fixtures/b1-prop-drilled-handler/app/DraftEditor.tsx
@@ -0,0 +1,14 @@
+import { EditorPanel } from "./EditorPanel";
+
+export function DraftEditor() {
+  const persistDraft = () => {
+    fetch("/api/drafts", { method: "POST", body: "{}" });
+  };
+
+  return (
+    <main>
+      <h1>Draft editor</h1>
+      <EditorPanel onPersist={persistDraft} />
+    </main>
+  );
+}
diff --git a/eval/fixtures/b1-prop-drilled-handler/app/EditorPanel.tsx b/eval/fixtures/b1-prop-drilled-handler/app/EditorPanel.tsx
new file mode 100644
index 0000000..7f1e184
--- /dev/null
+++ b/eval/fixtures/b1-prop-drilled-handler/app/EditorPanel.tsx
@@ -0,0 +1,11 @@
+import { Toolbar } from "./Toolbar";
+
+/** Inline-arrow hop: the prop is wrapped, not passed directly. */
+export function EditorPanel({ onPersist }: { onPersist: () => void }) {
+  return (
+    <section>
+      <h2>Editor tools</h2>
+      <Toolbar onSaveDraft={() => onPersist()} />
+    </section>
+  );
+}
diff --git a/eval/fixtures/b1-prop-drilled-handler/app/OrphanButton.tsx b/eval/fixtures/b1-prop-drilled-handler/app/OrphanButton.tsx
new file mode 100644
index 0000000..6378e1b
--- /dev/null
+++ b/eval/fixtures/b1-prop-drilled-handler/app/OrphanButton.tsx
@@ -0,0 +1,17 @@
+export function OrphanButton({ onMystery }: { onMystery?: () => void }) {
+  return (
+    <button type="button" onClick={onMystery}>
+      Mystery action
+    </button>
+  );
+}
+
+/** Renders OrphanButton without ever passing the handler — must flag, not guess. */
+export function OrphanHost() {
+  return (
+    <div>
+      <h3>Orphan host</h3>
+      <OrphanButton />
+    </div>
+  );
+}
diff --git a/eval/fixtures/b1-prop-drilled-handler/app/SaveButton.tsx b/eval/fixtures/b1-prop-drilled-handler/app/SaveButton.tsx
new file mode 100644
index 0000000..7e6b183
--- /dev/null
+++ b/eval/fixtures/b1-prop-drilled-handler/app/SaveButton.tsx
@@ -0,0 +1,7 @@
+export function SaveButton({ onSave }: { onSave: () => void }) {
+  return (
+    <button type="button" onClick={onSave}>
+      Save draft
+    </button>
+  );
+}
diff --git a/eval/fixtures/b1-prop-drilled-handler/app/Toolbar.tsx b/eval/fixtures/b1-prop-drilled-handler/app/Toolbar.tsx
new file mode 100644
index 0000000..4e79469
--- /dev/null
+++ b/eval/fixtures/b1-prop-drilled-handler/app/Toolbar.tsx
@@ -0,0 +1,10 @@
+import { SaveButton } from "./SaveButton";
+
+/** Renamed hop: the prop arrives as onSaveDraft, is passed down as onSave. */
+export function Toolbar({ onSaveDraft }: { onSaveDraft: () => void }) {
+  return (
+    <div role="toolbar">
+      <SaveButton onSave={onSaveDraft} />
+    </div>
+  );
+}
diff --git a/eval/fixtures/b1-prop-drilled-handler/golden.json b/eval/fixtures/b1-prop-drilled-handler/golden.json
new file mode 100644
index 0000000..f6c752f
--- /dev/null
+++ b/eval/fixtures/b1-prop-drilled-handler/golden.json
@@ -0,0 +1,29 @@
+{
+  "failureMode": "B1",
+  "note": "Callback prop-drilling, 4 levels: SaveButton.onClick={onSave} <- Toolbar (renamed prop) <- EditorPanel (inline arrow wrap) <- DraftEditor (real handler: fetch POST /api/drafts). Per-file analysis stops at the prop boundary; chain resolution must ground the event in the fetch. OrphanButton's never-passed handler must flag unresolved, not guess.",
+  "expect": {
+    "components": [
+      { "name": "SaveButton", "instances": 1 },
+      { "name": "Toolbar", "instances": 1 },
+      { "name": "EditorPanel", "instances": 1 },
+      { "name": "DraftEditor", "instances": 0 },
+      { "name": "OrphanButton", "instances": 1 }
+    ],
+    "attributions": [
+      { "component": "SaveButton", "endpoints": ["/api/drafts"] },
+      { "component": "OrphanButton", "endpoints": [] }
+    ],
+    "forbidden": [
+      {
+        "component": "OrphanButton",
+        "endpoint": "/api/drafts",
+        "note": "poison: an unrelated chain's endpoint attributed to the orphan"
+      }
+    ],
+    "queries": [
+      { "terms": ["Save draft"], "status": "ok", "top": "SaveButton" },
+      { "terms": ["Draft editor"], "status": "ok", "top": "DraftEditor" },
+      { "terms": ["Mystery action"], "status": "ok", "top": "OrphanButton" }
+    ]
+  }
+}
diff --git a/eval/history.jsonl b/eval/history.jsonl
index 332b128..27a667b 100644
--- a/eval/history.jsonl
+++ b/eval/history.jsonl
@@ -7,3 +7,4 @@
 {"generatedAt":"2026-07-13T11:04:05.130Z","commitSha":"d13b90dd99c993889f57218997984e3e2e601cfd","pass":91,"fail":0,"xfail":2,"unexpectedPass":0,"lineagePrecision":1,"lineageRecall":0.895,"matchAccuracy":1}
 {"generatedAt":"2026-07-13T11:10:56.348Z","commitSha":"b628c816231c4896f030ebc68a6621d0963d183c","pass":99,"fail":0,"xfail":2,"unexpectedPass":0,"lineagePrecision":1,"lineageRecall":0.895,"matchAccuracy":1}
 {"generatedAt":"2026-07-13T11:16:56.457Z","commitSha":"ce7a3bcbf95481114cd60ef62f8e840874ef7453","pass":108,"fail":0,"xfail":0,"unexpectedPass":0,"lineagePrecision":1,"lineageRecall":1,"matchAccuracy":1}
+{"generatedAt":"2026-07-13T11:25:04.854Z","commitSha":"cec11f7aab21ef6ec2d6dd0bb247e2cd29981ed9","pass":119,"fail":0,"xfail":0,"unexpectedPass":0,"lineagePrecision":1,"lineageRecall":1,"matchAccuracy":1}
diff --git a/packages/parser-react/src/handlers.test.ts b/packages/parser-react/src/handlers.test.ts
new file mode 100644
index 0000000..d030cf3
--- /dev/null
+++ b/packages/parser-react/src/handlers.test.ts
@@ -0,0 +1,43 @@
+import path from "node:path";
+import { fileURLToPath } from "node:url";
+
+import { traceLineage } from "@coderadar/core";
+import { describe, expect, it } from "vitest";
+
+import { scanReact } from "./scan.js";
+
+const fixture = path.resolve(
+  path.dirname(fileURLToPath(import.meta.url)),
+  "../../../eval/fixtures/b1-prop-drilled-handler/app",
+);
+
+const graph = scanReact({ root: fixture });
+
+describe("handler resolution through props (b1 fixture)", () => {
+  it("grounds a 4-level drilled handler in its fetch", () => {
+    const event = graph.nodes.find(
+      (n) => n.kind === "event" && n.handler === "onSave",
+    );
+    if (event === undefined) throw new Error("SaveButton onClick event not found");
+    const triggers = graph.edges.filter((e) => e.kind === "triggers" && e.from === event.id);
+    expect(triggers).toHaveLength(1);
+    const target = graph.nodes.find((n) => n.id === triggers[0]?.to);
+    expect(target?.kind === "data-source" ? `${target.method} ${target.endpoint}` : "missing").toBe(
+      "POST /api/drafts",
+    );
+  });
+
+  it("makes the endpoint reachable from SaveButton's lineage", () => {
+    const definition = graph.nodes.find((n) => n.kind === "component" && n.name === "SaveButton");
+    if (definition === undefined) throw new Error("SaveButton not found");
+    const lineage = traceLineage(graph, definition.id).candidates[0]?.value;
+    expect(lineage?.dataSources.map((d) => d.endpoint)).toEqual(["/api/drafts"]);
+  });
+
+  it("flags never-passed handlers as unresolved instead of guessing", () => {
+    const event = graph.nodes.find((n) => n.kind === "event" && n.handler === "onMystery");
+    if (event === undefined) throw new Error("OrphanButton onClick event not found");
+    expect(event.flags).toContain("unresolved-prop-handler");
+    expect(graph.edges.some((e) => e.kind === "triggers" && e.from === event.id)).toBe(false);
+  });
+});
diff --git a/packages/parser-react/src/scan.ts b/packages/parser-react/src/scan.ts
index f4fad36..f080a6b 100644
--- a/packages/parser-react/src/scan.ts
+++ b/packages/parser-react/src/scan.ts
@@ -177,6 +177,7 @@ export function scanReact(options: ScanOptions): LineageGraph {
     root,
   );
   resolvePropFlow(pendingInstances, instanceIds, nodes, edges, addEdge, baseUrls, wrappers);
+  resolveHandlerChains(pendingInstances, instanceIds, nodes, edges, addEdge, baseUrls, wrappers, root);
 
   return {
     version: 2,
@@ -1108,6 +1109,212 @@ function resolvePropFlow(
   }
 }
 
+/**
+ * Handler resolution through props (TRACKER step 2.3, failure mode B1).
+ *
+ * <button onClick={onSave}> where onSave is a PROP means the real handler
+ * lives at a call site — possibly four components up:
+ *
+ *   SaveButton onClick={onSave} ← Toolbar onSave={onSaveDraft}
+ *     ← EditorPanel onSaveDraft={() => onPersist()} ← DraftEditor onPersist={persistDraft}
+ *       → persistDraft body → fetch POST /api/drafts
+ *
+ * Resolved handler bodies are mined for data sources, emitted as
+ * event --triggers--> data-source edges (via: the instance id whose call
+ * chain produced them). Chains dead after MAX_HANDLER_DEPTH levels flag the
+ * event "unresolved-prop-handler" — visible, never silent.
+ */
+const MAX_HANDLER_DEPTH = 4;
+
+function resolveHandlerChains(
+  pendingInstances: PendingInstance[],
+  instanceIds: Array<string | null>,
+  nodes: Map<string, LineageNode>,
+  edges: LineageEdge[],
+  addEdge: (edge: LineageEdge) => void,
+  baseUrls: string[],
+  wrappers: WrapperRegistry,
+  root: string,
+): void {
+  const instancesByDefinition = new Map<string, Array<{ pending: PendingInstance; id: string }>>();
+  for (const [index, pending] of pendingInstances.entries()) {
+    const id = instanceIds[index];
+    if (id === null || id === undefined) continue;
+    const instance = nodes.get(id);
+    if (instance === undefined || instance.kind !== "instance") continue;
+    const list = instancesByDefinition.get(instance.definitionId);
+    if (list) list.push({ pending, id });
+    else instancesByDefinition.set(instance.definitionId, [{ pending, id }]);
+  }
+
+  const fileOf = (node: Node): string =>
+    toPosix(path.relative(root, node.getSourceFile().getFilePath()));
+
+  // Expression-bodied arrows (`() => onPersist()`) ARE the call — descendants
+  // alone would miss them.
+  const callsWithin = (body: Node): Node[] => [
+    ...(Node.isCallExpression(body) ? [body] : []),
+    ...body.getDescendantsOfKind(SyntaxKind.CallExpression),
+  ];
+
+  /** Collect data-source ids from a handler body, creating nodes as needed. */
+  const minePropHandlerBody = (body: Node, sources: Set<string>): void => {
+    for (const call of callsWithin(body)) {
+      if (!Node.isCallExpression(call)) continue;
+      const detected = detectDataSource(call, call.getExpression().getText(), baseUrls, wrappers);
+      if (detected === null) continue;
+      const file = fileOf(call);
+      const dsId = nodeId("data-source", file, `${detected.sourceKind}:${detected.endpoint}`);
+      if (!nodes.has(dsId)) {
+        nodes.set(dsId, {
+          id: dsId,
+          kind: "data-source",
+          name: detected.endpoint,
+          loc: locOf(call, file),
+          sourceKind: detected.sourceKind,
+          method: detected.method,
+          endpoint: detected.endpoint,
+          raw: detected.raw,
+          resolved: detected.resolved,
+        });
+      }
+      sources.add(dsId);
+    }
+  };
+
+  /** The prop's property name + default initializer on a definition's params. */
+  const propBinding = (
+    definitionId: string,
+    localName: string,
+  ): { propertyName: string; defaultInit: Node | undefined } | null => {
+    const definition = nodes.get(definitionId);
+    if (definition === undefined || definition.kind !== "component") return null;
+    if (!definition.props.includes(localName)) return null;
+    // Re-locate the AST: find the binding element for the local name.
+    const anyInstance = instancesByDefinition.get(definitionId)?.[0];
+    const sourceFile =
+      anyInstance?.pending.element.getSourceFile().getProject().getSourceFiles()
+        .find((f) => toPosix(path.relative(root, f.getFilePath())) === definition.loc.file) ??
+      undefined;
+    if (sourceFile === undefined) return { propertyName: localName, defaultInit: undefined };
+    for (const binding of sourceFile.getDescendantsOfKind(SyntaxKind.BindingElement)) {
+      if (binding.getName() !== localName) continue;
+      return {
+        propertyName: binding.getPropertyNameNode()?.getText() ?? localName,
+        defaultInit: binding.getInitializer(),
+      };
+    }
+    return { propertyName: localName, defaultInit: undefined };
+  };
+
+  /** Resolve a handler expression at a call site; returns whether anything grounded. */
+  const resolveExpr = (
+    expr: Node,
+    ownerDefinitionId: string,
+    depth: number,
+    sources: Set<string>,
+  ): boolean => {
+    if (depth > MAX_HANDLER_DEPTH) return false;
+
+    if (Node.isArrowFunction(expr) || Node.isFunctionExpression(expr)) {
+      const body = expr.getBody();
+      if (body === undefined) return false;
+      minePropHandlerBody(body, sources);
+      let grounded = sources.size > 0;
+      // Arrow wrapping a prop call: () => onPersist()
+      for (const call of callsWithin(body)) {
+        if (!Node.isCallExpression(call)) continue;
+        const callee = call.getExpression();
+        const calleeName = Node.isPropertyAccessExpression(callee)
+          ? callee.getExpression().getText().endsWith("props")
+            ? callee.getName()
+            : null
+          : Node.isIdentifier(callee)
+            ? callee.getText()
+            : null;
+        if (calleeName !== null && resolveChain(ownerDefinitionId, calleeName, depth + 1, sources)) {
+          grounded = true;
+        }
+      }
+      return grounded;
+    }
+
+    if (Node.isPropertyAccessExpression(expr) && expr.getExpression().getText().endsWith("props")) {
+      return resolveChain(ownerDefinitionId, expr.getName(), depth + 1, sources);
+    }
+
+    if (Node.isIdentifier(expr)) {
+      for (const definition of expr.getDefinitionNodes()) {
+        if (Node.isFunctionDeclaration(definition)) {
+          const body = definition.getBody();
+          if (body !== undefined) {
+            minePropHandlerBody(body, sources);
+            return true;
+          }
+        }
+        if (Node.isVariableDeclaration(definition)) {
+          const init = definition.getInitializer();
+          if (init !== undefined && (Node.isArrowFunction(init) || Node.isFunctionExpression(init))) {
+            return resolveExpr(init, ownerDefinitionId, depth, sources);
+          }
+        }
+        if (Node.isBindingElement(definition) || Node.isParameterDeclaration(definition)) {
+          // The handler is itself a prop of the owner — continue up the tree.
+          return resolveChain(ownerDefinitionId, expr.getText(), depth + 1, sources);
+        }
+      }
+    }
+    return false;
+  };
+
+  /** Follow a prop named `localName` on `definitionId` up through its call sites. */
+  const resolveChain = (
+    definitionId: string,
+    localName: string,
+    depth: number,
+    sources: Set<string>,
+  ): boolean => {
+    if (depth > MAX_HANDLER_DEPTH) return false;
+    const binding = propBinding(definitionId, localName);
+    if (binding === null) return false;
+    let grounded = false;
+    for (const { pending } of instancesByDefinition.get(definitionId) ?? []) {
+      let expr: Node | undefined = binding.defaultInit;
+      for (const attr of pending.element.getAttributes()) {
+        if (!Node.isJsxAttribute(attr) || attr.getNameNode().getText() !== binding.propertyName) {
+          continue;
+        }
+        const init = attr.getInitializer();
+        expr = init !== undefined && Node.isJsxExpression(init) ? init.getExpression() : undefined;
+        break;
+      }
+      if (expr === undefined) continue;
+      if (resolveExpr(expr, pending.ownerId, depth, sources)) grounded = true;
+    }
+    return grounded;
+  };
+
+  // Events whose handler is a prop of their own component: resolve the chain.
+  for (const edge of [...edges]) {
+    if (edge.kind !== "handles") continue;
+    const event = nodes.get(edge.to);
+    const owner = nodes.get(edge.from);
+    if (event === undefined || event.kind !== "event" || event.handler === null) continue;
+    if (owner === undefined || owner.kind !== "component") continue;
+    const bareName = event.handler.replace(/^(this\.)?props\./, "");
+    if (!owner.props.includes(bareName)) continue;
+
+    const sources = new Set<string>();
+    const grounded = resolveChain(owner.id, bareName, 1, sources);
+    for (const dsId of sources) {
+      addEdge({ from: event.id, to: dsId, kind: "triggers" });
+    }
+    if (!grounded) {
+      event.flags = [...(event.flags ?? []), "unresolved-prop-handler"];
+    }
+  }
+}
+
 /** Rewrite `unresolved-hook:<name>` placeholders to real hook node ids; drop misses. */
 export function resolveHookEdges(graph: LineageGraph): LineageGraph {
   const hooksByName = new Map<string, string>();