diff --git a/codex-rs/agent-identity/BUILD.bazel b/codex-rs/agent-identity/BUILD.bazel
index 3957a19a92..5f49ffb72e 100644
--- a/codex-rs/agent-identity/BUILD.bazel
+++ b/codex-rs/agent-identity/BUILD.bazel
@@ -3,7 +3,7 @@ load("//:defs.bzl", "codex_rust_crate")
 codex_rust_crate(
     name = "agent-identity",
     crate_name = "codex_agent_identity",
-    test_sizes = {
-        "agent-identity-unit-tests-windows-cross": "medium",
+    test_tags_by_target = {
+        "agent-identity-unit-tests-windows-cross": ["exclusive-if-local"],
     },
 )
diff --git a/codex-rs/apply-patch/BUILD.bazel b/codex-rs/apply-patch/BUILD.bazel
index df0e714b6f..468f606eca 100644
--- a/codex-rs/apply-patch/BUILD.bazel
+++ b/codex-rs/apply-patch/BUILD.bazel
@@ -3,7 +3,7 @@ load("//:defs.bzl", "codex_rust_crate")
 codex_rust_crate(
     name = "apply-patch",
     crate_name = "codex_apply_patch",
-    test_sizes = {
-        "apply-patch-all-test-windows-cross": "medium",
+    test_tags_by_target = {
+        "apply-patch-all-test-windows-cross": ["exclusive-if-local"],
     },
 )
diff --git a/codex-rs/file-system/BUILD.bazel b/codex-rs/file-system/BUILD.bazel
index 0e311a7a22..4fe0ec7a9d 100644
--- a/codex-rs/file-system/BUILD.bazel
+++ b/codex-rs/file-system/BUILD.bazel
@@ -3,7 +3,7 @@ load("//:defs.bzl", "codex_rust_crate")
 codex_rust_crate(
     name = "file-system",
     crate_name = "codex_file_system",
-    test_sizes = {
-        "file-system-unit-tests-windows-cross": "medium",
+    test_tags_by_target = {
+        "file-system-unit-tests-windows-cross": ["exclusive-if-local"],
     },
 )
diff --git a/codex-rs/memories/read/BUILD.bazel b/codex-rs/memories/read/BUILD.bazel
index 2e49f74659..fb101c8513 100644
--- a/codex-rs/memories/read/BUILD.bazel
+++ b/codex-rs/memories/read/BUILD.bazel
@@ -3,7 +3,7 @@ load("//:defs.bzl", "codex_rust_crate")
 codex_rust_crate(
     name = "read",
     crate_name = "codex_memories_read",
-    test_sizes = {
-        "read-unit-tests-windows-cross": "medium",
+    test_tags_by_target = {
+        "read-unit-tests-windows-cross": ["exclusive-if-local"],
     },
 )
diff --git a/codex-rs/secrets/BUILD.bazel b/codex-rs/secrets/BUILD.bazel
index ddd2f3e511..0fefc47377 100644
--- a/codex-rs/secrets/BUILD.bazel
+++ b/codex-rs/secrets/BUILD.bazel
@@ -3,7 +3,7 @@ load("//:defs.bzl", "codex_rust_crate")
 codex_rust_crate(
     name = "secrets",
     crate_name = "codex_secrets",
-    test_sizes = {
-        "secrets-unit-tests-windows-cross": "medium",
+    test_tags_by_target = {
+        "secrets-unit-tests-windows-cross": ["exclusive-if-local"],
     },
 )
diff --git a/codex-rs/state/BUILD.bazel b/codex-rs/state/BUILD.bazel
index 57a7ad22dd..acf31d0f91 100644
--- a/codex-rs/state/BUILD.bazel
+++ b/codex-rs/state/BUILD.bazel
@@ -9,7 +9,7 @@ codex_rust_crate(
         "migrations/**",
     ]),
     crate_name = "codex_state",
-    test_sizes = {
-        "state-unit-tests-windows-cross": "medium",
+    test_tags_by_target = {
+        "state-unit-tests-windows-cross": ["exclusive-if-local"],
     },
 )
diff --git a/codex-rs/utils/approval-presets/BUILD.bazel b/codex-rs/utils/approval-presets/BUILD.bazel
index 54e9aea292..c66b9887b5 100644
--- a/codex-rs/utils/approval-presets/BUILD.bazel
+++ b/codex-rs/utils/approval-presets/BUILD.bazel
@@ -3,7 +3,7 @@ load("//:defs.bzl", "codex_rust_crate")
 codex_rust_crate(
     name = "approval-presets",
     crate_name = "codex_utils_approval_presets",
-    test_sizes = {
-        "approval-presets-unit-tests-windows-cross": "medium",
+    test_tags_by_target = {
+        "approval-presets-unit-tests-windows-cross": ["exclusive-if-local"],
     },
 )
diff --git a/codex-rs/utils/rustls-provider/BUILD.bazel b/codex-rs/utils/rustls-provider/BUILD.bazel
index 4a8a4d9c7f..65c6206104 100644
--- a/codex-rs/utils/rustls-provider/BUILD.bazel
+++ b/codex-rs/utils/rustls-provider/BUILD.bazel
@@ -5,6 +5,8 @@ codex_rust_crate(
     crate_name = "codex_utils_rustls_provider",
     test_sizes = {
         "rustls-provider-preinstalled-test-windows-cross": "medium",
-        "rustls-provider-unit-tests-windows-cross": "medium",
+    },
+    test_tags_by_target = {
+        "rustls-provider-unit-tests-windows-cross": ["exclusive-if-local"],
     },
 )
diff --git a/codex-rs/windows-sandbox-rs/BUILD.bazel b/codex-rs/windows-sandbox-rs/BUILD.bazel
index c0c0f9ee7d..a4a7593bf7 100644
--- a/codex-rs/windows-sandbox-rs/BUILD.bazel
+++ b/codex-rs/windows-sandbox-rs/BUILD.bazel
@@ -6,7 +6,7 @@ codex_rust_crate(
         "codex-windows-sandbox-setup.manifest",
     ],
     crate_name = "codex_windows_sandbox",
-    test_sizes = {
-        "windows-sandbox-rs-unit-tests-windows-cross": "medium",
+    test_tags_by_target = {
+        "windows-sandbox-rs-unit-tests-windows-cross": ["exclusive-if-local"],
     },
 )
diff --git a/defs.bzl b/defs.bzl
index bdc9b09aeb..ff6907dcba 100644
--- a/defs.bzl
+++ b/defs.bzl
@@ -198,6 +198,7 @@ def codex_rust_crate(
         test_shard_counts = {},
         test_sizes = {},
         test_tags = [],
+        test_tags_by_target = {},
         unit_test_timeout = None,
         extra_binaries = [],
         extra_binaries_non_windows = [],
@@ -247,6 +248,8 @@ def codex_rust_crate(
             targets individually, including Windows-cross and Wine tests.
         test_tags: Tags applied to unit + integration test targets.
             Typically used to disable the sandbox, but see https://bazel.build/reference/be/common-definitions#common.tags
+        test_tags_by_target: Mapping from generated test target name to
+            additional Bazel tags for that target.
         unit_test_timeout: Optional Bazel timeout for the unit-test target
             generated from `src/**/*.rs`.
         extra_binaries: Additional binary labels to surface as test data and
@@ -378,7 +381,7 @@ def codex_rust_crate(
                 test_bin = ":" + unit_test_binary,
                 workspace_root_marker = "//codex-rs/utils/cargo-bin:repo_root.marker",
                 target_compatible_with = target_compatible_with,
-                tags = test_tags,
+                tags = _test_tags(test_tags, test_tags_by_target, unit_test_target_name),
                 **unit_test_kwargs
             )
 
@@ -528,7 +531,7 @@ def codex_rust_crate(
                 test_bin = ":" + integration_test_binary,
                 workspace_root_marker = "//codex-rs/utils/cargo-bin:repo_root.marker",
                 target_compatible_with = WINDOWS_GNULLVM_INCOMPATIBLE,
-                tags = test_tags,
+                tags = _test_tags(test_tags, test_tags_by_target, test_name),
                 **test_kwargs
             )
         else:
@@ -554,7 +557,7 @@ def codex_rust_crate(
                 rustc_env = rustc_env,
                 env = integration_test_cargo_env,
                 target_compatible_with = WINDOWS_GNULLVM_INCOMPATIBLE,
-                tags = test_tags,
+                tags = _test_tags(test_tags, test_tags_by_target, test_name),
                 **test_kwargs
             )
 
@@ -604,7 +607,7 @@ def codex_rust_crate(
                 test_bin = "//codex-rs/exec-server/testing:wine-exec-test-runner",
                 workspace_root_marker = "//codex-rs/utils/cargo-bin:repo_root.marker",
                 target_compatible_with = WINE_TEST_TARGET_COMPATIBLE_WITH,
-                tags = test_tags + ["manual"],
+                tags = _test_tags(test_tags, test_tags_by_target, wine_test_name) + ["manual"],
                 **wine_test_kwargs
             )
 
@@ -642,7 +645,7 @@ def codex_rust_crate(
             test_bin = ":" + windows_cross_test_binary,
             workspace_root_marker = "//codex-rs/utils/cargo-bin:repo_root.marker",
             target_compatible_with = WINDOWS_GNULLVM_ONLY,
-            tags = test_tags,
+            tags = _test_tags(test_tags, test_tags_by_target, windows_cross_test_name),
             **windows_cross_test_kwargs
         )
 
@@ -662,6 +665,14 @@ def codex_rust_crate(
     if unknown_test_shard_counts:
         fail("test_shard_counts contains unknown generated test targets: {}".format(", ".join(unknown_test_shard_counts)))
 
+    unknown_test_tags = sorted([
+        test_name
+        for test_name in test_tags_by_target
+        if test_name not in generated_test_names
+    ])
+    if unknown_test_tags:
+        fail("test_tags_by_target contains unknown generated test targets: {}".format(", ".join(unknown_test_tags)))
+
 def _test_shard_count(test_shard_counts, test_name):
     shard_count = test_shard_counts.get(test_name)
     if shard_count == None:
@@ -672,6 +683,9 @@ def _test_shard_count(test_shard_counts, test_name):
 
     return shard_count
 
+def _test_tags(test_tags, test_tags_by_target, test_name):
+    return test_tags + test_tags_by_target.get(test_name, [])
+
 def _test_size(test_sizes, test_name):
     size = test_sizes.get(test_name, "small")
     if size not in ["small", "medium", "large", "enormous"]: