feat(tools): file_read lists directory entries

When given a directory path, file_read now returns its entries (sorted,
sub-directories suffixed '/') instead of failing. The tool description
and path-param schema advertise this so the model discovers it rather
than giving up after a missing-file probe. Generalises file_read into a
'read this path' primitive; the existing PathJail/Plane-2 containment
already covers directories.

infrastructure/tools/filesystem/src/main/kotlin/com/correx/infrastructure/tools/filesystem/FileReadTool.kt

@@ -26,6 +26,8 @@ import java.nio.file.Files
 import java.nio.file.InvalidPathException
 import java.nio.file.Path
 import java.nio.file.Paths
+import kotlin.io.path.listDirectoryEntries
+import kotlin.io.path.name
 
 class FileReadTool(
     private val allowedPaths: Set<Path> = emptySet(),
@@ -45,13 +47,18 @@ class FileReadTool(
     }
 
     override val name: String = "file_read"
-    override val description: String = "Read content from a file at the specified path"
+    override val description: String =
+        "Read a file's contents, or list a directory's entries, at the specified path"
     override val parametersSchema: JsonObject = buildJsonObject {
         put("type", "object")
         putJsonObject("properties") {
             putJsonObject("path") {
                 put("type", "string")
-                put("description", "Relative path to the file to read")
+                put(
+                    "description",
+                    "Relative path. A file path returns the file's contents; a directory path " +
+                        "returns its entries, one per line, with sub-directories suffixed '/'.",
+                )
             }
             putJsonObject("start_line") {
                 put("type", "integer")
@@ -123,7 +130,14 @@ class FileReadTool(
                 recoverable = true,
             )
 
-        runCatching {
+        if (Files.isDirectory(path)) {
+            listDir(path, request)
+        } else {
+            readFile(path, startLine, endLine, request)
+        }
+    }
+
+    private fun readFile(path: Path, startLine: Int?, endLine: Int?, request: ToolRequest): ToolResult = runCatching {
         val lines = Files.readAllLines(path)
         val start = ((startLine ?: 1) - 1).coerceAtLeast(0)
         val end = (endLine ?: lines.size).coerceAtMost(lines.size)
@@ -139,5 +153,21 @@ class FileReadTool(
             recoverable = false,
         )
     }
+
+    private fun listDir(path: Path, request: ToolRequest): ToolResult = runCatching {
+        val entries = path.listDirectoryEntries().sortedBy { it.name }
+        val output = entries.joinToString("\n") { entry ->
+            if (Files.isDirectory(entry)) "${entry.name}/" else entry.name
+        }
+        ToolResult.Success(
+            invocationId = request.invocationId,
+            output = output,
+        )
+    }.getOrElse {
+        ToolResult.Failure(
+            invocationId = request.invocationId,
+            reason = "Failed to list dir: ${it.message}",
+            recoverable = false,
+        )
     }
 }

infrastructure/tools/filesystem/src/test/kotlin/com/correx/infrastructure/tools/filesystem/FileReadToolTest.kt

@@ -112,6 +112,21 @@ class FileReadToolTest {
         assertTrue(failure.reason.contains("is not in the allowed list"))
     }
 
+    @Test
+    fun `execute lists directory entries sorted with sub-directory marker`(): Unit = runBlocking {
+        val tempDir = Files.createTempDirectory("test_listdir")
+        Files.writeString(tempDir.resolve("README.md"), "x")
+        Files.writeString(tempDir.resolve("build.gradle"), "x")
+        Files.createDirectory(tempDir.resolve("src"))
+
+        val tool = FileReadTool(allowedPaths = setOf(tempDir))
+        val result = tool.execute(createRequest(tempDir.toString()))
+
+        assertTrue(result is ToolResult.Success)
+        // Sorted by name; directories suffixed with '/' so the model can navigate.
+        assertEquals("README.md\nbuild.gradle\nsrc/", (result as ToolResult.Success).output)
+    }
+
     @Test
     fun `outputCompressor strips blank lines and leading whitespace`() {
         val tool = FileReadTool()