diff --git a/docs/development/testing.md b/docs/development/testing.md
index ecebe4a920..9a2a23844b 100644
--- a/docs/development/testing.md
+++ b/docs/development/testing.md
@@ -239,7 +239,9 @@ changes additionally need package verification; provider changes need actual
 provider evidence.
 
 Vitest projects use up to two workers, bounded by host parallelism. GitHub
-Actions jobs own their runner and use up to four.
+Actions jobs own their runner and use up to four. Test deadlines are 30 seconds,
+or 60 with coverage; hosted CI doubles both because CPU-bound cases there share
+every core with other workers and their subprocesses.
 `process-boundary` runs later with serial files because process-tree sampling
 shares host resources. Acceptance and process-global cases use isolated forks
 without serial scheduling. Pure domain/service, composition, conformance,
diff --git a/tests/boundary/filesystem/ciTestProjects.test.ts b/tests/boundary/filesystem/ciTestProjects.test.ts
index 0e6c0baec2..ee76728f6f 100644
--- a/tests/boundary/filesystem/ciTestProjects.test.ts
+++ b/tests/boundary/filesystem/ciTestProjects.test.ts
@@ -1,5 +1,6 @@
 import { execFileSync } from "node:child_process";
 import { mkdir, writeFile } from "node:fs/promises";
+import { availableParallelism } from "node:os";
 import { join } from "node:path";
 import { pathToFileURL } from "node:url";
 
@@ -161,34 +162,42 @@ describe("Vitest project configuration", () => {
     );
   });
 
-  it.each([
-    { flags: [], timeout: 30_000, lines: 68 },
-    { flags: ["--coverage"], timeout: 60_000, lines: 68 },
-    { flags: ["--coverage.enabled"], timeout: 60_000, lines: 68 },
-    { flags: ["--coverage=false"], timeout: 30_000, lines: 68 },
-    {
-      flags: ["--coverage.enabled=false"],
-      timeout: 30_000,
-      lines: 68,
-    },
-    {
-      flags: ["--coverage.provider=v8"],
-      timeout: 30_000,
-      lines: 68,
-    },
-    {
-      flags: ["--coverage.enabled", "--shard", "1/6"],
-      timeout: 60_000,
-      lines: 0,
-    },
-    {
-      flags: ["--coverage.enabled=false", "--shard=1/6"],
-      timeout: 30_000,
-      lines: 0,
-    },
-  ])(
-    "resolves worker resources from actual CLI options: $flags",
-    async ({ flags, timeout, lines }) => {
+  it.each(
+    [
+      { flags: [], timeout: 30_000, lines: 68 },
+      { flags: ["--coverage"], timeout: 60_000, lines: 68 },
+      { flags: ["--coverage.enabled"], timeout: 60_000, lines: 68 },
+      { flags: ["--coverage=false"], timeout: 30_000, lines: 68 },
+      {
+        flags: ["--coverage.enabled=false"],
+        timeout: 30_000,
+        lines: 68,
+      },
+      {
+        flags: ["--coverage.provider=v8"],
+        timeout: 30_000,
+        lines: 68,
+      },
+      {
+        flags: ["--coverage.enabled", "--shard", "1/6"],
+        timeout: 60_000,
+        lines: 0,
+      },
+      {
+        flags: ["--coverage.enabled=false", "--shard=1/6"],
+        timeout: 30_000,
+        lines: 0,
+      },
+    ].flatMap((policy) =>
+      // Hosted CI owns a four-core runner: up to four workers, doubled deadlines.
+      [
+        { ...policy, hosted: false, workers: 2, scale: 1 },
+        { ...policy, hosted: true, workers: 4, scale: 2 },
+      ],
+    ),
+  )(
+    "resolves worker resources from actual CLI options: $flags (hosted: $hosted)",
+    async ({ flags, timeout, lines, hosted, workers, scale }) => {
       const root = await createTestTempDirectory("rea-vitest-worker-policy-");
       const script = join(root, "worker-policy.mjs");
       await writeFile(
@@ -200,6 +209,7 @@ describe("Vitest project configuration", () => {
         execArgv: project.test.execArgv,
         timeout: config.test.testTimeout,
         lines: config.test.coverage.thresholds.lines,
+        workers: config.test.maxWorkers,
       }));
     `,
       );
@@ -208,6 +218,8 @@ describe("Vitest project configuration", () => {
         ["--import", "tsx", script, ...flags],
         {
           cwd: repository,
+          // Select the runner explicitly; CI itself sets GITHUB_ACTIONS.
+          env: { ...process.env, GITHUB_ACTIONS: hosted ? "true" : "" },
           timeout: 10_000,
           maxBuffer: 64 * 1024,
           stopSignal: "SIGTERM",
@@ -215,8 +227,9 @@ describe("Vitest project configuration", () => {
       );
       expect(JSON.parse(result.stdout)).toEqual({
         execArgv: ["--max-old-space-size=512"],
-        timeout,
+        timeout: timeout * scale,
         lines,
+        workers: Math.min(workers, availableParallelism()),
       });
     },
   );
diff --git a/tests/boundary/javascript/semanticFingerprintAccumulation.test.ts b/tests/boundary/javascript/semanticFingerprintAccumulation.test.ts
index 7c642f10ef..c8603ca5d0 100644
--- a/tests/boundary/javascript/semanticFingerprintAccumulation.test.ts
+++ b/tests/boundary/javascript/semanticFingerprintAccumulation.test.ts
@@ -94,5 +94,8 @@ it.each(["direct", "transferred"] as const)(
       });
     }
   },
-  30_000,
+  // About 22 s of CPU-bound projection on a typical hosted runner. A suite
+  // deadline of 30 s fails it on slower runners, and an explicit 30 s also
+  // removed the suite's longer coverage-mode allowance.
+  60_000,
 );
diff --git a/vitest.config.ts b/vitest.config.ts
index da60fe65ed..64a5ce846a 100644
--- a/vitest.config.ts
+++ b/vitest.config.ts
@@ -150,8 +150,11 @@ export default defineConfig({
     runner: "./tests/processOwnershipRunner.ts",
     // Boundary projects may compete with TypeScript, docs, and package checks
     // under Turbo. Keep the deadline bounded while avoiding false failures from
-    // host-level CPU and filesystem contention.
-    testTimeout: COVERAGE_ENABLED ? 60_000 : 30_000,
+    // host-level CPU and filesystem contention. Hosted CI runs a worker per
+    // core, so CPU-bound cases share the runner with each other's subprocesses;
+    // the deadline still bounds a hang there, at twice the local allowance.
+    testTimeout:
+      (COVERAGE_ENABLED ? 60_000 : 30_000) * (DEDICATED_CI_RUNNER ? 2 : 1),
     coverage: {
       enabled: false,
       provider: "v8",