diff --git a/src/application/ReferenceSourceImport.ts b/src/application/ReferenceSourceImport.ts
index 769f8bb8cd..f917f1965e 100644
--- a/src/application/ReferenceSourceImport.ts
+++ b/src/application/ReferenceSourceImport.ts
@@ -12,7 +12,7 @@ import type { ArtifactResourceScope } from "../artifacts/ArtifactResourceScope.j
 import type { AnalysisCleanupObservation } from "../domain/analysisErrorBase.js";
 import { readReferenceSource } from "../reference/ReferenceSourceReader.js";
 import type {
-  ReferenceSourceEntryKind,
+  ReferenceSourceExclusionKind,
   ReferenceSourceRead,
   ReferenceSourceReaderError,
 } from "../reference/ReferenceSourceReaderTypes.js";
@@ -111,7 +111,8 @@ const deriveInventoryState = (
       entry.limitations.length > 0 ||
       (entry.kind === "file" && entry.content_state !== "hashed") ||
       (entry.kind === "directory" && entry.tree_state !== "enumerated") ||
-      (entry.kind === "symlink" && entry.target_state !== "internal"),
+      (entry.kind === "symlink" && entry.target_state !== "internal") ||
+      entry.kind === "unknown",
   );
   if (partialEntry) return "partial";
   const partialRelationship = input.relationships.some(
@@ -142,11 +143,24 @@ const createShouldExclude =
     exclusions: HistoricalSourceGraphInput["exclusions"],
     secrets: PreparedReferenceSourceImport["secrets"],
     ignored: PreparedReferenceSourceImport["ignored"],
-  ): ((path: string, kind: ReferenceSourceEntryKind) => boolean) =>
+  ): ((path: string, kind: ReferenceSourceExclusionKind) => boolean) =>
   (path, kind) => {
-    const patternPath = kind === "directory" ? `${path}/` : path;
-    const secretMatch = secrets.test(patternPath);
-    if (secretMatch.ignored) {
+    // An entry of unknown kind may be a directory, so directory-only rules
+    // must still exclude it; this fails closed for caller-marked secrets.
+    const patternPaths =
+      kind === "directory"
+        ? [`${path}/`]
+        : kind === "unknown"
+          ? [path, `${path}/`]
+          : [path];
+    const firstMatch = (matcher: typeof secrets) => {
+      const results = patternPaths.map((patternPath) =>
+        matcher.test(patternPath),
+      );
+      return results.find(({ ignored }) => ignored) ?? results[0];
+    };
+    const secretMatch = firstMatch(secrets);
+    if (secretMatch?.ignored === true) {
       if (!secretMatch.rule)
         throw new Error(`Ignored secret path has no matching rule: ${path}`);
       exclusions.push({
@@ -156,8 +170,8 @@ const createShouldExclude =
       });
       return true;
     }
-    const match = ignored.test(patternPath);
-    if (!match.ignored) return false;
+    const match = firstMatch(ignored);
+    if (match?.ignored !== true) return false;
     if (!match.rule)
       throw new Error(`Ignored path has no matching rule: ${path}`);
     const reason = match.rule.mark;
diff --git a/src/application/ReferenceSourceImportEntries.ts b/src/application/ReferenceSourceImportEntries.ts
index 49c6f82f54..29dbef3568 100644
--- a/src/application/ReferenceSourceImportEntries.ts
+++ b/src/application/ReferenceSourceImportEntries.ts
@@ -45,6 +45,8 @@ const entryRecoveryGuidance = (
     return "This directory could not be read. Check its permissions, then try again.";
   if (entry.kind === "symlink")
     return "This symbolic link could not be read safely. Check the link and its permissions, then try again.";
+  if (entry.kind === "unknown")
+    return "This entry's type could not be determined. Check the parent directory and try again.";
   return "This file could not be read. Check its permissions, then try again.";
 };
 
@@ -73,6 +75,13 @@ const failedEntry = (
       classifications,
       limitations: [limitation],
     };
+  if (entry.kind === "unknown")
+    return {
+      path: entry.path,
+      kind: "unknown",
+      classifications: ["unknown"],
+      limitations: [limitation],
+    };
   return {
     path: entry.path,
     kind: "file",
diff --git a/src/domain/referenceSourceGraph.test.ts b/src/domain/referenceSourceGraph.test.ts
index 1286cdde6b..8fe868832c 100644
--- a/src/domain/referenceSourceGraph.test.ts
+++ b/src/domain/referenceSourceGraph.test.ts
@@ -259,6 +259,30 @@ describe("historical source graph", () => {
 });
 
 describe("partial historical source graphs", () => {
+  it("keeps unknown-entry diagnostics outside the root commitment", () => {
+    const base = graphInput();
+    base.inventory_state = "partial";
+    base.entries[2] = {
+      path: "src/package.json",
+      kind: "unknown",
+      classifications: ["unknown"],
+      limitations: ["Permission denied at /private/first"],
+    };
+    const graph = createHistoricalSourceGraph(base);
+    const changedMessage = structuredClone(base);
+    changedMessage.entries[2] = {
+      path: "src/package.json",
+      kind: "unknown",
+      classifications: ["unknown"],
+      limitations: ["Permission denied at /private/second"],
+    };
+    const revised = createHistoricalSourceGraph(changedMessage);
+    expect(revised.root_sha256).toBe(graph.root_sha256);
+    expect(computeHistoricalSourceGraphSha256(revised)).not.toBe(
+      computeHistoricalSourceGraphSha256(graph),
+    );
+  });
+
   it("keeps an unreadable symlink target unknown and out of root identity", () => {
     const base = graphInput();
     base.inventory_state = "partial";
diff --git a/src/domain/referenceSourceGraph.ts b/src/domain/referenceSourceGraph.ts
index 197e473bfc..a830e0aa05 100644
--- a/src/domain/referenceSourceGraph.ts
+++ b/src/domain/referenceSourceGraph.ts
@@ -111,6 +111,10 @@ const sourceEntrySchema = z.union([
   sourceFileSchema,
   sourceDirectorySchema,
   sourceSymlinkSchema,
+  z.strictObject({
+    ...entryBaseShape,
+    kind: z.literal("unknown"),
+  }),
 ]);
 
 const sourceRelationshipSchema = z.strictObject({
@@ -361,7 +365,8 @@ const checkCompleteInventory = (
       entry.limitations.length > 0 ||
       (entry.kind === "file" && entry.content_state !== "hashed") ||
       (entry.kind === "directory" && entry.tree_state !== "enumerated") ||
-      (entry.kind === "symlink" && entry.target_state !== "internal"),
+      (entry.kind === "symlink" && entry.target_state !== "internal") ||
+      entry.kind === "unknown",
   );
   const partialRelationship = graph.relationships.some(
     ({ parse_state, resolution }) =>
@@ -478,6 +483,11 @@ const rootCommitment = (
           target: entry.target,
           target_state: entry.target_state,
         };
+      case "unknown":
+        return {
+          kind: entry.kind,
+          path: entry.path,
+        };
     }
   }),
   exclusions,
diff --git a/src/domain/referenceSourceSummary.test.ts b/src/domain/referenceSourceSummary.test.ts
index a0d23b0e16..3f34a073f4 100644
--- a/src/domain/referenceSourceSummary.test.ts
+++ b/src/domain/referenceSourceSummary.test.ts
@@ -81,6 +81,26 @@ describe("committed historical-source summaries", () => {
     expect(graph).toEqual(original);
   });
 
+  it("counts entries of unknown kind separately from symlinks", () => {
+    const graph = createHistoricalSourceGraph(
+      input([
+        {
+          path: "deep",
+          kind: "unknown",
+          classifications: ["unknown"],
+          limitations: ["lstat: ENAMETOOLONG"],
+        },
+      ]),
+    );
+    expect(createHistoricalSourceSummary(graph, 1).counts).toMatchObject({
+      entries: 1,
+      files: 0,
+      directories: 0,
+      symlinks: 0,
+      unknown: 1,
+    });
+  });
+
   it("sums known bytes losslessly beyond the JSON safe integer range", () => {
     const graph = createHistoricalSourceGraph(
       input(
diff --git a/src/domain/referenceSourceSummary.ts b/src/domain/referenceSourceSummary.ts
index e7e99e3fa9..55d24025d2 100644
--- a/src/domain/referenceSourceSummary.ts
+++ b/src/domain/referenceSourceSummary.ts
@@ -29,6 +29,7 @@ export const createHistoricalSourceSummary = (
     files: 0,
     directories: 0,
     symlinks: 0,
+    unknown: 0,
     relationships: graph.relationships.length,
     parse_failures: graph.parse_failures.length,
     exclusions: graph.exclusions.length,
@@ -59,7 +60,8 @@ export const createHistoricalSourceSummary = (
     } else if (entry.kind === "directory") {
       counts.directories += 1;
       treeStates[entry.tree_state] += 1;
-    } else counts.symlinks += 1;
+    } else if (entry.kind === "symlink") counts.symlinks += 1;
+    else counts.unknown += 1;
     // Canonical entries already use Unicode code-point order; filtering preserves it.
     if (entry.path.split("/").length <= outlineDepth)
       outline.push(outlineEntry(entry));
diff --git a/src/reference/ReferenceSourceReaderEntries.ts b/src/reference/ReferenceSourceReaderEntries.ts
index e684a2b5cb..8ec5e9d803 100644
--- a/src/reference/ReferenceSourceReaderEntries.ts
+++ b/src/reference/ReferenceSourceReaderEntries.ts
@@ -25,7 +25,7 @@ import {
 import type {
   PendingDirectory,
   ReferenceSourceEntry,
-  ReferenceSourceEntryKind,
+  ReferenceSourceExclusionKind,
   ReferenceSourceResult,
   TraversalState,
 } from "./ReferenceSourceReaderTypes.js";
@@ -201,6 +201,13 @@ const processEntry = async (
   const metadata = await readMetadata(absolute);
   if (isAborted(state.signal)) return { ok: false, error: cancelled() };
   if (!metadata.ok) {
+    const excluded = applyExclusion(state.shouldExclude, path, "unknown");
+    if (!excluded.ok)
+      return {
+        ok: false,
+        error: failure("io", "Reference source exclusion check failed"),
+      };
+    if (excluded.value) return { ok: true, value: undefined };
     state.entries.push(entryFailure(path, "unknown", "io", metadata.message));
     return { ok: true, value: undefined };
   }
@@ -371,10 +378,10 @@ const readSymlinkTarget = async (
 
 const applyExclusion = (
   shouldExclude:
-    | ((path: string, kind: ReferenceSourceEntryKind) => boolean)
+    | ((path: string, kind: ReferenceSourceExclusionKind) => boolean)
     | undefined,
   path: string,
-  kind: ReferenceSourceEntryKind,
+  kind: ReferenceSourceExclusionKind,
 ): { readonly ok: true; readonly value: boolean } | { readonly ok: false } => {
   try {
     return { ok: true, value: shouldExclude?.(path, kind) === true };
diff --git a/src/reference/ReferenceSourceReaderErrors.ts b/src/reference/ReferenceSourceReaderErrors.ts
index 6ddd02a3f2..2c826b4c96 100644
--- a/src/reference/ReferenceSourceReaderErrors.ts
+++ b/src/reference/ReferenceSourceReaderErrors.ts
@@ -29,6 +29,9 @@ const FILESYSTEM_ERROR_CODES = new Set([
   "EISDIR",
   "ELOOP",
   "EMFILE",
+  // A traversed child can exceed the platform's absolute path limit even
+  // though the selected root and every component are valid.
+  "ENAMETOOLONG",
   "ENFILE",
   "ENOENT",
   "ENOTDIR",
@@ -44,6 +47,8 @@ export const filesystemFailureDetail = (
 ): string | undefined => {
   if (!(cause instanceof Error)) return undefined;
   const code: unknown = Reflect.get(cause, "code");
+  if (code === "ENAMETOOLONG")
+    return `${operation}: ENAMETOOLONG (entry path exceeds the operating system path limit)`;
   return typeof code === "string" && FILESYSTEM_ERROR_CODES.has(code)
     ? `${operation}: ${cause.message}`
     : undefined;
diff --git a/src/reference/ReferenceSourceReaderTypes.ts b/src/reference/ReferenceSourceReaderTypes.ts
index 3b0a368b51..1fec383131 100644
--- a/src/reference/ReferenceSourceReaderTypes.ts
+++ b/src/reference/ReferenceSourceReaderTypes.ts
@@ -10,11 +10,17 @@ export type ReferenceSourceEntryKind =
   | "symlink"
   | "other";
 
+/**
+ * Kind offered to exclusion predicates. `unknown` marks an entry whose
+ * metadata could not be read, so its concrete kind cannot be claimed.
+ */
+export type ReferenceSourceExclusionKind = ReferenceSourceEntryKind | "unknown";
+
 export interface ReferenceSourceReaderOptions {
   readonly signal?: AbortSignal;
   readonly shouldExclude?: (
     path: string,
-    kind: ReferenceSourceEntryKind,
+    kind: ReferenceSourceExclusionKind,
   ) => boolean;
 }
 
@@ -84,7 +90,7 @@ export type TraversalState = {
   readonly signal?: AbortSignal;
   readonly shouldExclude?: (
     path: string,
-    kind: ReferenceSourceEntryKind,
+    kind: ReferenceSourceExclusionKind,
   ) => boolean;
   readonly entries: ReferenceSourceEntry[];
   readonly pending: PendingDirectory[];
diff --git a/tests/boundary/filesystem/referenceSourceFailureDetails.test.ts b/tests/boundary/filesystem/referenceSourceFailureDetails.test.ts
index dd87ea92a2..82476d6db8 100644
--- a/tests/boundary/filesystem/referenceSourceFailureDetails.test.ts
+++ b/tests/boundary/filesystem/referenceSourceFailureDetails.test.ts
@@ -133,3 +133,88 @@ describe("reference import native entry failure details", () => {
     ).toMatchObject({ kind: "file", content_state: "hashed", limitations: [] });
   });
 });
+
+describe("reference import paths beyond the platform limit", () => {
+  it.skipIf(process.platform === "win32")(
+    "reports an entry beyond the absolute path limit as an I/O failure",
+    async () => {
+      const root = await createTestTempDirectory("rea-import-deep-path-");
+      await writeFile(join(root, "kept.txt"), "k");
+      // Relative creation lets the tree exceed PATH_MAX (1024 on macOS, 4096
+      // on Linux) while each 200-byte component stays below NAME_MAX.
+      const deepTree = (action: "create" | "remove") =>
+        promisify(execFile)(process.execPath, [
+          "-e",
+          `const fs = require("node:fs");
+          const names = Array.from({ length: 24 }, (_, i) => "d" + String(i).padStart(2, "0") + "x".repeat(197));
+          process.chdir(${JSON.stringify(root)});
+          if (${JSON.stringify(action)} === "create") {
+            for (const name of names) { fs.mkdirSync(name); process.chdir(name); }
+            fs.writeFileSync("deep.txt", "d");
+          } else {
+            for (const name of names) process.chdir(name);
+            fs.rmSync("deep.txt");
+            for (const name of [...names].reverse()) { process.chdir(".."); fs.rmdirSync(name); }
+          }`,
+        ]);
+      await deepTree("create");
+      try {
+        const read = await readReferenceSource(root);
+        if (!read.ok) throw new Error(read.error.message);
+        expect(read.value.entries).toContainEqual(
+          expect.objectContaining({ path: "kept.txt", status: "read" }),
+        );
+        const failed = read.value.entries.find(
+          (entry) => entry.status === "failed",
+        );
+        expect(failed).toMatchObject({
+          status: "failed",
+          code: "io",
+          message: expect.stringContaining("ENAMETOOLONG"),
+        });
+        const filteredRead = await readReferenceSource(root, {
+          shouldExclude: (path, kind) =>
+            path === failed?.path && kind === "directory",
+        });
+        if (!filteredRead.ok) throw new Error(filteredRead.error.message);
+        expect(
+          filteredRead.value.entries.find(
+            (entry) => entry.path === failed?.path,
+          ),
+        ).toMatchObject({ status: "failed", kind: "unknown", code: "io" });
+        const imported = await importTree(root);
+        if (!imported.ok) throw new Error(imported.error.message);
+        expect(imported.value.entries).toContainEqual(
+          expect.objectContaining({
+            path: "kept.txt",
+            content_state: "hashed",
+          }),
+        );
+        const deep = imported.value.entries.find(
+          (entry) => entry.path === failed?.path,
+        );
+        expect(deep?.limitations.join(" ")).toContain(
+          failed?.status === "failed" ? failed.message : "missing failure",
+        );
+        // A directory-only secret rule still applies when the kind is unknown.
+        const secretPattern = `${failed?.path ?? "missing"}/`;
+        const secret = await importReferenceSource({
+          root,
+          caller: "native-entry-failure-detail-test",
+          policy: { secretPatterns: [secretPattern] },
+        });
+        if (!secret.ok) throw new Error(secret.error.message);
+        expect(
+          secret.value.entries.some(({ path }) => path === failed?.path),
+        ).toBe(false);
+        expect(secret.value.exclusions).toContainEqual({
+          path: failed?.path,
+          reason: "configured-secret",
+          pattern: secretPattern,
+        });
+      } finally {
+        await deepTree("remove");
+      }
+    },
+  );
+});