fix(security): add archive extraction containment validation

Validate tar and zip entries before extraction to prevent path traversal:
- Reject absolute paths in archives
- Reject .. traversal paths
- Reject symlinks pointing outside extraction dir
- New archive-entry-validator module with comprehensive tests

Addresses: security audit finding for unsafe archive extraction.

src/shared/zip-entry-listing.ts

@@ -0,0 +1,122 @@
+import { spawn } from "bun"
+
+import type { ArchiveEntry } from "./archive-entry-validator"
+
+function parseTarListedZipEntry(line: string): ArchiveEntry | null {
+	const match = line.match(/^([^\s])\S*\s+\d+\s+\S+\s+\S+\s+\d+\s+\w+\s+\d+\s+(?:\d{2}:\d{2}|\d{4})\s+(.*)$/)
+	if (!match) {
+		return null
+	}
+
+	const [, rawType, rawEntryPath] = match
+	if (rawType === "l") {
+		const arrowIndex = rawEntryPath.lastIndexOf(" -> ")
+		return {
+			path: arrowIndex === -1 ? rawEntryPath : rawEntryPath.slice(0, arrowIndex),
+			type: "symlink",
+			linkPath: arrowIndex === -1 ? undefined : rawEntryPath.slice(arrowIndex + 4),
+		}
+	}
+
+	return {
+		path: rawEntryPath,
+		type: rawType === "d" ? "directory" : "file",
+	}
+}
+
+export async function listZipEntriesWithTar(archivePath: string): Promise<ArchiveEntry[]> {
+	const proc = spawn(["tar", "-tvf", archivePath], {
+		stdout: "pipe",
+		stderr: "pipe",
+	})
+
+	const [exitCode, stdout, stderr] = await Promise.all([
+		proc.exited,
+		new Response(proc.stdout).text(),
+		new Response(proc.stderr).text(),
+	])
+
+	if (exitCode !== 0) {
+		throw new Error(`zip entry listing failed (exit ${exitCode}): ${stderr}`)
+	}
+
+	return stdout
+		.split(/\r?\n/)
+		.map(line => line.trim())
+		.filter(Boolean)
+		.map(line => parseTarListedZipEntry(line))
+		.filter((entry): entry is ArchiveEntry => entry !== null)
+}
+
+export async function listZipEntriesWithPowerShell(
+	archivePath: string,
+	escapePowerShellPath: (path: string) => string,
+	extractor: "pwsh" | "powershell"
+): Promise<ArchiveEntry[]> {
+	const proc = spawn(
+		[
+			extractor,
+			"-Command",
+			[
+				"Add-Type -AssemblyName System.IO.Compression.FileSystem",
+				`$archive = [System.IO.Compression.ZipFile]::OpenRead('${escapePowerShellPath(archivePath)}')`,
+				"try {",
+				"  foreach ($entry in $archive.Entries) {",
+				"    $mode = ($entry.ExternalAttributes -shr 16) -band 0xFFFF",
+				"    $type = if (($mode -band 0xF000) -eq 0xA000) { 'symlink' } elseif ($entry.FullName.EndsWith('/')) { 'directory' } else { 'file' }",
+				"    $target = ''",
+				"    if ($type -eq 'symlink') {",
+				"      $stream = $entry.Open()",
+				"      try {",
+				"        $reader = New-Object System.IO.StreamReader($stream)",
+				"        try { $target = $reader.ReadToEnd() } finally { $reader.Dispose() }",
+				"      } finally { $stream.Dispose() }",
+				"    }",
+				"    Write-Output ($type + \"`t\" + $entry.FullName + \"`t\" + $target)",
+				"  }",
+				"} finally {",
+				"  $archive.Dispose()",
+				"}",
+			].join("; "),
+		],
+		{
+			stdout: "pipe",
+			stderr: "pipe",
+		}
+	)
+
+	const [exitCode, stdout, stderr] = await Promise.all([
+		proc.exited,
+		new Response(proc.stdout).text(),
+		new Response(proc.stderr).text(),
+	])
+
+	if (exitCode !== 0) {
+		throw new Error(`zip entry listing failed (exit ${exitCode}): ${stderr}`)
+	}
+
+	return stdout
+		.split(/\r?\n/)
+		.map(line => line.trim())
+		.filter(Boolean)
+		.map((line): ArchiveEntry | null => {
+			const [type, entryPath, linkPath = ""] = line.split("\t")
+			if (type !== "file" && type !== "directory" && type !== "symlink") {
+				return null
+			}
+
+			if (type === "symlink") {
+				return {
+					path: entryPath,
+					type,
+					linkPath,
+				}
+			}
+
+			return {
+				path: entryPath,
+				type,
+			}
+		})
+		.filter((entry): entry is ArchiveEntry => entry !== null)
+}