diff --git a/infrastructure/tools/filesystem/src/main/kotlin/com/correx/infrastructure/tools/filesystem/FileEditTool.kt b/infrastructure/tools/filesystem/src/main/kotlin/com/correx/infrastructure/tools/filesystem/FileEditTool.kt
index ecc7fd1f..1cad3684 100644
--- a/infrastructure/tools/filesystem/src/main/kotlin/com/correx/infrastructure/tools/filesystem/FileEditTool.kt
+++ b/infrastructure/tools/filesystem/src/main/kotlin/com/correx/infrastructure/tools/filesystem/FileEditTool.kt
@@ -134,9 +134,7 @@ class FileEditTool(
     }
 
     private fun isPathAllowed(path: Path): Boolean =
-        normalizedAllowedPaths.any { allowedPath ->
-            path.startsWith(allowedPath)
-        }
+        PathJail.isContained(path, normalizedAllowedPaths)
 
     private fun mapExceptionToValidationResult(e: Throwable): ValidationResult =
         when (e) {
diff --git a/infrastructure/tools/filesystem/src/main/kotlin/com/correx/infrastructure/tools/filesystem/FileReadTool.kt b/infrastructure/tools/filesystem/src/main/kotlin/com/correx/infrastructure/tools/filesystem/FileReadTool.kt
index b0a70c9a..2a956702 100644
--- a/infrastructure/tools/filesystem/src/main/kotlin/com/correx/infrastructure/tools/filesystem/FileReadTool.kt
+++ b/infrastructure/tools/filesystem/src/main/kotlin/com/correx/infrastructure/tools/filesystem/FileReadTool.kt
@@ -62,8 +62,8 @@ class FileReadTool(
             return ValidationResult.Invalid("'end_line' must be >= 'start_line'.")
 
         return runCatching {
-            val path = Paths.get(pathString).normalize().toAbsolutePath()
-            if (allowedPaths.isNotEmpty() && allowedPaths.none { path.startsWith(it.normalize().toAbsolutePath()) })
+            val path = Paths.get(pathString)
+            if (!PathJail.isContained(path, allowedPaths))
                 ValidationResult.Invalid("Path '$pathString' is not in the allowed list")
             else
                 ValidationResult.Valid
diff --git a/infrastructure/tools/filesystem/src/main/kotlin/com/correx/infrastructure/tools/filesystem/FileWriteTool.kt b/infrastructure/tools/filesystem/src/main/kotlin/com/correx/infrastructure/tools/filesystem/FileWriteTool.kt
index a59dd91d..4817cb4d 100644
--- a/infrastructure/tools/filesystem/src/main/kotlin/com/correx/infrastructure/tools/filesystem/FileWriteTool.kt
+++ b/infrastructure/tools/filesystem/src/main/kotlin/com/correx/infrastructure/tools/filesystem/FileWriteTool.kt
@@ -132,9 +132,7 @@ class FileWriteTool(
     }
 
     private fun isPathAllowed(path: Path): Boolean =
-        normalizedAllowedPaths.any { allowedPath ->
-            path.startsWith(allowedPath)
-        }
+        PathJail.isContained(path, normalizedAllowedPaths)
 
     private fun mapExceptionToValidationResult(e: Throwable): ValidationResult =
         when (e) {
diff --git a/infrastructure/tools/filesystem/src/main/kotlin/com/correx/infrastructure/tools/filesystem/PathJail.kt b/infrastructure/tools/filesystem/src/main/kotlin/com/correx/infrastructure/tools/filesystem/PathJail.kt
new file mode 100644
index 00000000..1ee19977
--- /dev/null
+++ b/infrastructure/tools/filesystem/src/main/kotlin/com/correx/infrastructure/tools/filesystem/PathJail.kt
@@ -0,0 +1,45 @@
+package com.correx.infrastructure.tools.filesystem
+
+import java.nio.file.Files
+import java.nio.file.Path
+
+/**
+ * Symlink-safe path containment for the filesystem tools' jail. Mirrors the
+ * materializer's discipline (resolve, then enforce containment) but adds
+ * [Path.toRealPath] resolution so a symlink living inside an allowed directory
+ * cannot smuggle access to a target outside it. Fails CLOSED: an empty
+ * allow-list contains nothing.
+ */
+internal object PathJail {
+
+    /**
+     * Resolve [path] to a symlink-resolved absolute path. If the target does not
+     * exist yet (new-file writes), resolve the nearest existing ancestor via
+     * [Path.toRealPath] and re-append the not-yet-created segments — so a
+     * symlinked ancestor is still followed to its real location before the
+     * containment check.
+     */
+    fun realize(path: Path): Path {
+        val absolute = path.toAbsolutePath().normalize()
+        var existing: Path? = absolute
+        val missing = ArrayDeque<Path>()
+        while (existing != null && !Files.exists(existing)) {
+            existing.fileName?.let { missing.addFirst(it) }
+            existing = existing.parent
+        }
+        val anchor = existing ?: return absolute
+        val real = runCatching { anchor.toRealPath() }.getOrDefault(anchor)
+        return missing.fold(real) { acc, segment -> acc.resolve(segment) }.normalize()
+    }
+
+    /**
+     * True iff [path] resolves inside one of [allowedRoots]. Empty roots ⇒ false
+     * (fail closed). Both the candidate and each root are symlink-resolved before
+     * comparison.
+     */
+    fun isContained(path: Path, allowedRoots: Set<Path>): Boolean {
+        if (allowedRoots.isEmpty()) return false
+        val real = realize(path)
+        return allowedRoots.any { real.startsWith(realize(it)) }
+    }
+}
diff --git a/infrastructure/tools/filesystem/src/test/kotlin/com/correx/infrastructure/tools/filesystem/PathJailTest.kt b/infrastructure/tools/filesystem/src/test/kotlin/com/correx/infrastructure/tools/filesystem/PathJailTest.kt
new file mode 100644
index 00000000..a6e2606b
--- /dev/null
+++ b/infrastructure/tools/filesystem/src/test/kotlin/com/correx/infrastructure/tools/filesystem/PathJailTest.kt
@@ -0,0 +1,47 @@
+package com.correx.infrastructure.tools.filesystem
+
+import org.junit.jupiter.api.Assertions.assertFalse
+import org.junit.jupiter.api.Assertions.assertTrue
+import org.junit.jupiter.api.Test
+import java.nio.file.Files
+
+class PathJailTest {
+
+    @Test
+    fun `empty allow-list fails closed`() {
+        val dir = Files.createTempDirectory("jail").toRealPath()
+        assertFalse(PathJail.isContained(dir.resolve("f.txt"), emptySet()))
+    }
+
+    @Test
+    fun `path inside an allowed root is contained`() {
+        val root = Files.createTempDirectory("jail-in").toRealPath()
+        assertTrue(PathJail.isContained(root.resolve("sub/f.txt"), setOf(root)))
+    }
+
+    @Test
+    fun `path outside all allowed roots is rejected`() {
+        val root = Files.createTempDirectory("jail-root").toRealPath()
+        val other = Files.createTempDirectory("jail-other").toRealPath()
+        assertFalse(PathJail.isContained(other.resolve("f.txt"), setOf(root)))
+    }
+
+    @Test
+    fun `non-existent target under an allowed root is contained`() {
+        val root = Files.createTempDirectory("jail-new").toRealPath()
+        assertTrue(PathJail.isContained(root.resolve("does/not/exist/yet.txt"), setOf(root)))
+    }
+
+    @Test
+    fun `symlink inside an allowed root that points outside is rejected`() {
+        val root = Files.createTempDirectory("jail-link-root").toRealPath()
+        val outside = Files.createTempDirectory("jail-link-escape").toRealPath()
+        Files.writeString(outside.resolve("secret.txt"), "secret")
+        val link = root.resolve("escape")
+        Files.createSymbolicLink(link, outside)
+
+        // Without toRealPath() this string-prefixes inside root and would be allowed;
+        // symlink-resolved it lands in `outside`, so it must be rejected.
+        assertFalse(PathJail.isContained(link.resolve("secret.txt"), setOf(root)))
+    }
+}