diff --git a/Sources/CodexBarCore/Generated/CodexParserHash.generated.swift b/Sources/CodexBarCore/Generated/CodexParserHash.generated.swift
index 2a1047a65a..a27b750991 100644
--- a/Sources/CodexBarCore/Generated/CodexParserHash.generated.swift
+++ b/Sources/CodexBarCore/Generated/CodexParserHash.generated.swift
@@ -1,5 +1,5 @@
 // Generated by Scripts/regenerate-codex-parser-hash.sh. Do not edit by hand.
 
 enum CodexParserHash {
-    static let value = "865e101428b49ab7"
+    static let value = "f1fe17eb233c9f4d"
 }
diff --git a/Sources/CodexBarCore/Providers/Codex/CodexLineageDiscovery.swift b/Sources/CodexBarCore/Providers/Codex/CodexLineageDiscovery.swift
new file mode 100644
index 0000000000..0b75a82e87
--- /dev/null
+++ b/Sources/CodexBarCore/Providers/Codex/CodexLineageDiscovery.swift
@@ -0,0 +1,137 @@
+import Foundation
+
+/// Expands an already bounded rollout-file selection with only the ancestors its documents reference.
+enum CodexLineageDiscovery {
+    struct Report: Equatable, Sendable {
+        let documents: [CodexLineageLedger.Document]
+        let referencedParentDocumentCount: Int
+        let unresolvedParentIDs: Set<String>
+    }
+
+    static func discover(
+        includedFiles: [URL],
+        roots: [URL],
+        checkCancellation: CostUsageScanner.CancellationCheck? = nil) throws -> Report
+    {
+        var locator = ParentFileLocator(roots: roots, checkCancellation: checkCancellation)
+        var documents: [CodexLineageLedger.Document] = []
+        var knownIDs: Set<String> = []
+        var seenPaths: Set<String> = []
+        var pendingParentIDs: [String] = []
+        var unresolvedParentIDs: Set<String> = []
+        var referencedParentDocumentCount = 0
+
+        func remember(_ document: CodexLineageLedger.Document) {
+            documents.append(document)
+            knownIDs.insert(Self.canonicalSessionID(document.ownerID))
+            if let metadataSessionID = Self.nonEmpty(document.metadataSessionID) {
+                knownIDs.insert(Self.canonicalSessionID(metadataSessionID))
+            }
+            if let parentSessionID = Self.nonEmpty(document.parentSessionID) {
+                pendingParentIDs.append(Self.canonicalSessionID(parentSessionID))
+            }
+        }
+
+        for fileURL in includedFiles.sorted(by: { $0.path < $1.path }) {
+            try checkCancellation?()
+            let path = fileURL.standardizedFileURL.path
+            guard seenPaths.insert(path).inserted else { continue }
+            try remember(CostUsageScanner.parseCodexLineageDocument(
+                fileURL: fileURL,
+                checkCancellation: checkCancellation))
+        }
+
+        var nextParent = 0
+        while nextParent < pendingParentIDs.count {
+            try checkCancellation?()
+            let parentID = pendingParentIDs[nextParent]
+            nextParent += 1
+            guard !knownIDs.contains(parentID), !unresolvedParentIDs.contains(parentID) else { continue }
+            guard let parentURL = try locator.fileURL(for: parentID) else {
+                unresolvedParentIDs.insert(parentID)
+                continue
+            }
+            let path = parentURL.standardizedFileURL.path
+            guard seenPaths.insert(path).inserted else {
+                unresolvedParentIDs.insert(parentID)
+                continue
+            }
+            let parent = try CostUsageScanner.parseCodexLineageDocument(
+                fileURL: parentURL,
+                checkCancellation: checkCancellation)
+            let ownerID = Self.canonicalSessionID(parent.ownerID)
+            let metadataSessionID = parent.metadataSessionID.map(Self.canonicalSessionID)
+            guard ownerID == parentID || metadataSessionID == parentID else {
+                unresolvedParentIDs.insert(parentID)
+                continue
+            }
+            referencedParentDocumentCount += 1
+            remember(parent)
+        }
+
+        return Report(
+            documents: documents,
+            referencedParentDocumentCount: referencedParentDocumentCount,
+            unresolvedParentIDs: unresolvedParentIDs)
+    }
+
+    private static func nonEmpty(_ value: String?) -> String? {
+        guard let value, !value.isEmpty else { return nil }
+        return value
+    }
+
+    private static func canonicalSessionID(_ value: String) -> String {
+        UUID(uuidString: value)?.uuidString.lowercased() ?? value
+    }
+
+    private struct ParentFileLocator {
+        let roots: [URL]
+        let checkCancellation: CostUsageScanner.CancellationCheck?
+        var didIndexRoots = false
+        var filesByID: [String: URL] = [:]
+
+        mutating func fileURL(for sessionID: String) throws -> URL? {
+            let canonicalID = CodexLineageDiscovery.canonicalSessionID(sessionID)
+            if let known = self.filesByID[canonicalID] {
+                return known
+            }
+            if !self.didIndexRoots {
+                try self.indexRoots()
+            }
+            return self.filesByID[canonicalID]
+        }
+
+        private mutating func indexRoots() throws {
+            self.didIndexRoots = true
+            var files: [URL] = []
+            for root in self.roots {
+                try self.checkCancellation?()
+                guard let enumerator = FileManager.default.enumerator(
+                    at: root,
+                    includingPropertiesForKeys: [.isRegularFileKey],
+                    options: [.skipsHiddenFiles, .skipsPackageDescendants])
+                else { continue }
+                while let fileURL = enumerator.nextObject() as? URL {
+                    try self.checkCancellation?()
+                    guard fileURL.pathExtension.lowercased() == "jsonl" else { continue }
+                    files.append(fileURL)
+                }
+            }
+
+            for fileURL in files.sorted(by: { $0.path < $1.path }) {
+                try self.checkCancellation?()
+                if let ownerID = CostUsageScanner.codexRolloutOwnerID(fileURL: fileURL) {
+                    let canonicalID = CodexLineageDiscovery.canonicalSessionID(ownerID)
+                    self.filesByID[canonicalID] = self.filesByID[canonicalID] ?? fileURL
+                }
+                if let metadataID = try CostUsageScanner.parseCodexSessionIdentifier(
+                    fileURL: fileURL,
+                    checkCancellation: self.checkCancellation)
+                {
+                    let canonicalID = CodexLineageDiscovery.canonicalSessionID(metadataID)
+                    self.filesByID[canonicalID] = self.filesByID[canonicalID] ?? fileURL
+                }
+            }
+        }
+    }
+}
diff --git a/Sources/CodexBarCore/Vendored/CostUsage/CostUsageScanner.swift b/Sources/CodexBarCore/Vendored/CostUsage/CostUsageScanner.swift
index 9bda419158..b52b9e4bac 100644
--- a/Sources/CodexBarCore/Vendored/CostUsage/CostUsageScanner.swift
+++ b/Sources/CodexBarCore/Vendored/CostUsage/CostUsageScanner.swift
@@ -1829,7 +1829,7 @@ enum CostUsageScanner {
         CodexLineageLedger.Totals(input: totals.input, cached: totals.cached, output: totals.output)
     }
 
-    private static func codexRolloutOwnerID(fileURL: URL) -> String? {
+    static func codexRolloutOwnerID(fileURL: URL) -> String? {
         let stem = fileURL.deletingPathExtension().lastPathComponent
         guard stem.count >= 36 else { return nil }
         let candidate = String(stem.suffix(36))
diff --git a/Tests/CodexBarTests/CodexLineageDiscoveryTests.swift b/Tests/CodexBarTests/CodexLineageDiscoveryTests.swift
new file mode 100644
index 0000000000..9ab3126144
--- /dev/null
+++ b/Tests/CodexBarTests/CodexLineageDiscoveryTests.swift
@@ -0,0 +1,120 @@
+import Foundation
+import Testing
+@testable import CodexBarCore
+
+struct CodexLineageDiscoveryTests {
+    @Test
+    func `referenced parents cross the normal window and active archive roots transitively`() throws {
+        let environment = try CostUsageTestEnvironment()
+        defer { environment.cleanup() }
+        let grandparentID = "11111111-1111-4111-8111-111111111111"
+        let parentID = "22222222-2222-4222-8222-222222222222"
+        let childID = "33333333-3333-4333-8333-333333333333"
+        let unrelatedID = "44444444-4444-4444-8444-444444444444"
+        let grandparent = try Self.writeRollout(
+            root: environment.codexArchivedSessionsRoot,
+            relativeDirectory: "",
+            ownerID: grandparentID,
+            metadataID: grandparentID)
+        let parent = try Self.writeRollout(
+            root: environment.codexSessionsRoot,
+            relativeDirectory: "2025/01/01",
+            ownerID: parentID,
+            metadataID: parentID,
+            parentID: grandparentID)
+        let child = try Self.writeRollout(
+            root: environment.codexSessionsRoot,
+            relativeDirectory: "2026/07/09",
+            ownerID: childID,
+            metadataID: childID,
+            parentID: parentID)
+        _ = try Self.writeRollout(
+            root: environment.codexArchivedSessionsRoot,
+            relativeDirectory: "",
+            ownerID: unrelatedID,
+            metadataID: unrelatedID)
+
+        let report = try CodexLineageDiscovery.discover(
+            includedFiles: [child],
+            roots: [environment.codexSessionsRoot, environment.codexArchivedSessionsRoot])
+
+        #expect(Set(report.documents.map(\.ownerID)) == [childID, parentID, grandparentID])
+        #expect(report.documents.map(\.ownerID).contains(unrelatedID) == false)
+        #expect(report.referencedParentDocumentCount == 2)
+        #expect(report.unresolvedParentIDs.isEmpty)
+        #expect(FileManager.default.fileExists(atPath: parent.path))
+        #expect(FileManager.default.fileExists(atPath: grandparent.path))
+    }
+
+    @Test
+    func `missing referenced parents are diagnosed without widening included documents`() throws {
+        let environment = try CostUsageTestEnvironment()
+        defer { environment.cleanup() }
+        let child = try Self.writeRollout(
+            root: environment.codexSessionsRoot,
+            relativeDirectory: "2026/07/09",
+            ownerID: "55555555-5555-4555-8555-555555555555",
+            metadataID: "55555555-5555-4555-8555-555555555555",
+            parentID: "66666666-6666-4666-8666-666666666666")
+
+        let report = try CodexLineageDiscovery.discover(
+            includedFiles: [child],
+            roots: [environment.codexSessionsRoot, environment.codexArchivedSessionsRoot])
+
+        #expect(report.documents.count == 1)
+        #expect(report.referencedParentDocumentCount == 0)
+        #expect(report.unresolvedParentIDs == ["66666666-6666-4666-8666-666666666666"])
+    }
+
+    @Test
+    func `uuid parent references are matched case insensitively against filename owners`() throws {
+        let environment = try CostUsageTestEnvironment()
+        defer { environment.cleanup() }
+        let parentID = "aaaaaaaa-aaaa-4aaa-8aaa-aaaaaaaaaaaa"
+        _ = try Self.writeRollout(
+            root: environment.codexArchivedSessionsRoot,
+            relativeDirectory: "",
+            ownerID: parentID,
+            metadataID: "parent-metadata-alias")
+        let child = try Self.writeRollout(
+            root: environment.codexSessionsRoot,
+            relativeDirectory: "2026/07/09",
+            ownerID: "bbbbbbbb-bbbb-4bbb-8bbb-bbbbbbbbbbbb",
+            metadataID: "child-metadata",
+            parentID: parentID.uppercased())
+
+        let report = try CodexLineageDiscovery.discover(
+            includedFiles: [child],
+            roots: [environment.codexSessionsRoot, environment.codexArchivedSessionsRoot])
+
+        #expect(report.documents.map(\.ownerID).contains(parentID))
+        #expect(report.referencedParentDocumentCount == 1)
+        #expect(report.unresolvedParentIDs.isEmpty)
+    }
+
+    private static func writeRollout(
+        root: URL,
+        relativeDirectory: String,
+        ownerID: String,
+        metadataID: String,
+        parentID: String? = nil) throws -> URL
+    {
+        let directory = relativeDirectory.isEmpty
+            ? root
+            : root.appendingPathComponent(relativeDirectory, isDirectory: true)
+        try FileManager.default.createDirectory(at: directory, withIntermediateDirectories: true)
+        let fileURL = directory.appendingPathComponent(
+            "rollout-2025-01-01T00-00-00-\(ownerID).jsonl")
+        var metadata = #"{"type":"session_meta","payload":{"id":"\#(metadataID)""#
+        if let parentID {
+            metadata += #", "forked_from_id":"\#(parentID)""#
+        }
+        metadata += "}}\n"
+        metadata += #"{"type":"event_msg","timestamp":"2026-07-09T12:00:00Z","payload":{"#
+        metadata += #""type":"token_count","info":{"last_token_usage":{"input_tokens":10,"#
+        metadata += #""cached_input_tokens":0,"output_tokens":1},"total_token_usage":{"input_tokens":10,"#
+        metadata += #""cached_input_tokens":0,"output_tokens":1}}}}"#
+        try metadata.write(to: fileURL, atomically: true, encoding: .utf8)
+        return fileURL
+    }
+}