diff --git a/packages/runtime/src/scr_map.test.ts b/packages/runtime/src/scr_map.test.ts
index b567884fc..035b3a0eb 100644
--- a/packages/runtime/src/scr_map.test.ts
+++ b/packages/runtime/src/scr_map.test.ts
@@ -14,7 +14,14 @@ test("number-key maps keep Map semantics across linear, direct and hashed indexe
   try {
     await exec("clang", [
       "-std=c11",
-      "-O1",
+      // The runtime link set includes scr_json.c, scr_lib.c and scr_hash.c.
+      // With ASan/UBSan their optimized builds dominate the test's cost: -O1
+      // takes about 90s (scr_hash.c alone 29s, its unrolled digest rounds
+      // instrumented) and regularly starved past this test's timeout when the
+      // lane shared the box. The test checks Map semantics under sanitizers,
+      // not codegen, so -O0 keeps every assertion and sanitizer check and
+      // builds in about 15s.
+      "-O0",
       "-Wall",
       "-Wextra",
       "-fsanitize=address,undefined",
diff --git a/tests/harness/three-library.test.ts b/tests/harness/three-library.test.ts
index 23aa4c5e6..b14c9b779 100644
--- a/tests/harness/three-library.test.ts
+++ b/tests/harness/three-library.test.ts
@@ -7,59 +7,68 @@ import { skipUnownedTest } from "./shard.js";
 
 const fixture = join(import.meta.dirname, "../library-mode/wasm");
 const hasClang = spawnSync("clang", ["--version"]).status === 0;
+// Release compiles the whole three.js library into one LLVM module that a
+// single process optimizes and codegens on one core, which takes 5-10
+// minutes; sanitized dev builds are slower still. Lanes measured 331-581s for
+// release against the old 600s budget, so both get 1_200_000ms. The plain dev
+// case runs at about a fifth of release and keeps 600_000ms.
+function timeoutFor(optimization: "dev" | "release"): number {
+  return optimization === "release" || process.env["SCRIPTC_SAN"] === "1" ? 1_200_000 : 600_000;
+}
 // The two optimizations take similar time (about 10 minutes each under ASan):
 // SCRIPTC_TEST_SHARD runs them on different shards (tests/harness/shard.ts).
 // skipUnownedTest partitions a describe block's tests.
 describe("three.js native library", () => {
   beforeEach((context) => skipUnownedTest(context, {}));
-  test.skipIf(!hasClang).each(["dev", "release"] as const)(
-    "three.js sends animated geometry, materials and resource lifecycle to a native host in %s",
-    async (optimization) => {
-      const directory = await mkdtemp("/tmp/scriptc-three-library-");
-      const sanitize = process.env["SCRIPTC_SAN"] === "1";
-      try {
-        const profile = JSON.parse(await readFile(join(fixture, "three.json"), "utf8"));
-        const profilePath = join(directory, "profile.json");
-        await writeFile(
-          profilePath,
-          JSON.stringify({
-            ...profile,
-            name: "three-native-embedding",
-            entry: join(fixture, "three.mjs"),
-            optimization,
-          }),
-        );
-        const built = await compileLibrary({ profilePath, outDir: directory, sanitize });
-        if (!built.ok)
-          throw new Error(
-            built.diagnostics
-              .map((diagnostic) => `${diagnostic.code}: ${diagnostic.message}`)
-              .join("\n"),
+  for (const optimization of ["dev", "release"] as const) {
+    test.skipIf(!hasClang)(
+      `three.js sends animated geometry, materials and resource lifecycle to a native host in ${optimization}`,
+      async () => {
+        const directory = await mkdtemp("/tmp/scriptc-three-library-");
+        const sanitize = process.env["SCRIPTC_SAN"] === "1";
+        try {
+          const profile = JSON.parse(await readFile(join(fixture, "three.json"), "utf8"));
+          const profilePath = join(directory, "profile.json");
+          await writeFile(
+            profilePath,
+            JSON.stringify({
+              ...profile,
+              name: "three-native-embedding",
+              entry: join(fixture, "three.mjs"),
+              optimization,
+            }),
           );
-        const binary = join(directory, "host");
-        const linked = spawnSync(
-          "clang",
-          [
-            "-std=c11",
-            ...(sanitize ? ["-fsanitize=address,undefined"] : []),
-            join(fixture, "three-native.c"),
-            built.archivePath,
-            "-lm",
-            "-o",
-            binary,
-          ],
-          { encoding: "utf8" },
-        );
-        expect(linked.status, linked.stderr).toBe(0);
-        const actual = spawnSync(binary, [], { encoding: "utf8", timeout: 30_000 });
-        expect(actual.status, actual.stderr).toBe(0);
-        const reference = spawnSync(
-          process.execPath,
-          [
-            "--no-warnings",
-            "--input-type=module",
-            "-e",
-            `
+          const built = await compileLibrary({ profilePath, outDir: directory, sanitize });
+          if (!built.ok)
+            throw new Error(
+              built.diagnostics
+                .map((diagnostic) => `${diagnostic.code}: ${diagnostic.message}`)
+                .join("\n"),
+            );
+          const binary = join(directory, "host");
+          const linked = spawnSync(
+            "clang",
+            [
+              "-std=c11",
+              ...(sanitize ? ["-fsanitize=address,undefined"] : []),
+              join(fixture, "three-native.c"),
+              built.archivePath,
+              "-lm",
+              "-o",
+              binary,
+            ],
+            { encoding: "utf8" },
+          );
+          expect(linked.status, linked.stderr).toBe(0);
+          const actual = spawnSync(binary, [], { encoding: "utf8", timeout: 30_000 });
+          expect(actual.status, actual.stderr).toBe(0);
+          const reference = spawnSync(
+            process.execPath,
+            [
+              "--no-warnings",
+              "--input-type=module",
+              "-e",
+              `
       const events=[];
       for (const name of ["vertex","surface","resource"]) globalThis[name]=(...values)=>events.push([name,...values.map(value=>Number(value.toFixed(9)))]);
       const {frame,dispose}=await import(${JSON.stringify(join(fixture, "three.mjs"))});
@@ -67,21 +76,22 @@ describe("three.js native library", () => {
       dispose();
       console.log(JSON.stringify(events));
     `,
-          ],
-          { encoding: "utf8" },
-        );
-        expect(reference.status, reference.stderr).toBe(0);
-        const events = JSON.parse(reference.stdout);
-        expect(
-          actual.stdout
-            .trim()
-            .split("\n")
-            .map((line) => JSON.parse(line)),
-        ).toEqual([...events, ...events]);
-      } finally {
-        await rm(directory, { recursive: true, force: true });
-      }
-    },
-    600_000,
-  );
+            ],
+            { encoding: "utf8" },
+          );
+          expect(reference.status, reference.stderr).toBe(0);
+          const events = JSON.parse(reference.stdout);
+          expect(
+            actual.stdout
+              .trim()
+              .split("\n")
+              .map((line) => JSON.parse(line)),
+          ).toEqual([...events, ...events]);
+        } finally {
+          await rm(directory, { recursive: true, force: true });
+        }
+      },
+      timeoutFor(optimization),
+    );
+  }
 });