diff --git a/scripts/test-parallel.mjs b/scripts/test-parallel.mjs
index 89ab426ebd2..5016d34b612 100644
--- a/scripts/test-parallel.mjs
+++ b/scripts/test-parallel.mjs
@@ -267,6 +267,7 @@ const parseEnvNumber = (name, fallback) => {
   return Number.isFinite(parsed) && parsed >= 0 ? parsed : fallback;
 };
 const shardedCi = isCI && shardCount > 1;
+const shardedLinuxCi = shardedCi && !isWindows && !isMacOS;
 const allKnownUnitFiles = allKnownTestFiles.filter((file) => {
   return isUnitConfigTestFile(file);
 });
@@ -312,6 +313,9 @@ const timedHeavyUnitFiles =
 const unitFastExcludedFiles = [
   ...new Set([...unitBehaviorOverrideSet, ...timedHeavyUnitFiles, ...channelSingletonFiles]),
 ];
+// Sharded Linux CI still sees the broadest heap retention in the shared unit-fast lane. Prefer
+// process forks there so the workers release memory more aggressively between files.
+const unitFastPool = useVmForks && !shardedLinuxCi ? "vmForks" : "forks";
 const estimateUnitDurationMs = (file) =>
   unitTimingManifest.files[file]?.durationMs ?? unitTimingManifest.defaultDurationMs;
 const heavyUnitBuckets = packFilesByDuration(
@@ -333,7 +337,7 @@ const baseRuns = [
             "run",
             "--config",
             "vitest.unit.config.ts",
-            `--pool=${useVmForks ? "vmForks" : "forks"}`,
+            `--pool=${unitFastPool}`,
             ...(disableIsolation ? ["--isolate=false"] : []),
             ...unitFastExcludedFiles.flatMap((file) => ["--exclude", file]),
           ],
@@ -700,6 +704,9 @@ const maxWorkersForRun = (name) => {
   if (resolvedOverride) {
     return resolvedOverride;
   }
+  if (shardedLinuxCi && name === "unit-fast") {
+    return 1;
+  }
   if (name.endsWith("-threads") || name.endsWith("-vmforks")) {
     return 1;
   }
@@ -1191,7 +1198,10 @@ if (passthroughRequiresSingleRun && passthroughOptionArgs.length > 0) {
   process.exit(2);
 }
 
-if (isMacMiniProfile && targetedEntries.length === 0) {
+const shouldFrontloadUnitFast =
+  targetedEntries.length === 0 && (isMacMiniProfile || shardedLinuxCi);
+
+if (shouldFrontloadUnitFast) {
   const unitFastEntry = parallelRuns.find((entry) => entry.name === "unit-fast");
   if (unitFastEntry) {
     const unitFastCode = await run(unitFastEntry, passthroughOptionArgs);
@@ -1200,13 +1210,13 @@ if (isMacMiniProfile && targetedEntries.length === 0) {
     }
   }
   const deferredEntries = parallelRuns.filter((entry) => entry.name !== "unit-fast");
-  const failedMacMiniParallel = await runEntriesWithLimit(
+  const failedDeferredParallel = await runEntriesWithLimit(
     deferredEntries,
     passthroughOptionArgs,
-    3,
+    isMacMiniProfile ? 3 : topLevelParallelLimit,
   );
-  if (failedMacMiniParallel !== undefined) {
-    process.exit(failedMacMiniParallel);
+  if (failedDeferredParallel !== undefined) {
+    process.exit(failedDeferredParallel);
   }
 } else {
   const failedParallel = await runEntries(parallelRuns, passthroughOptionArgs);
diff --git a/test/fixtures/test-parallel.behavior.json b/test/fixtures/test-parallel.behavior.json
index 451ee637ef7..7d78be813de 100644
--- a/test/fixtures/test-parallel.behavior.json
+++ b/test/fixtures/test-parallel.behavior.json
@@ -278,6 +278,54 @@
       {
         "file": "src/tui/tui.submit-handler.test.ts",
         "reason": "TUI submit handler coverage retained the largest shared unit-fast heap spike in the March 20, 2026 Linux Node 24 shard 1 OOM lane."
+      },
+      {
+        "file": "src/cron/isolated-agent.uses-last-non-empty-agent-text-as.test.ts",
+        "reason": "Isolated-agent last-non-empty text coverage retained the largest shared unit-fast heap spike in the March 20, 2026 Linux Node 24 shard 1 rerun OOM lane."
+      },
+      {
+        "file": "src/infra/restart.test.ts",
+        "reason": "Restart coverage retained a top shared unit-fast heap spike in the March 20, 2026 Linux Node 24 shard 1 rerun OOM lane."
+      },
+      {
+        "file": "src/infra/update-runner.test.ts",
+        "reason": "Update runner coverage retained a top shared unit-fast heap spike in the March 20, 2026 Linux Node 24 shard 1 rerun OOM lane."
+      },
+      {
+        "file": "src/plugins/commands.test.ts",
+        "reason": "Plugin commands coverage retained a top shared unit-fast heap spike in the March 20, 2026 Linux Node 24 shard 1 rerun OOM lane."
+      },
+      {
+        "file": "src/infra/outbound/message-action-runner.context.test.ts",
+        "reason": "Message action runner context coverage retained a top shared unit-fast heap spike in the March 20, 2026 Linux Node 24 shard 1 rerun OOM lane."
+      },
+      {
+        "file": "src/cron/service.main-job-passes-heartbeat-target-last.test.ts",
+        "reason": "Cron main-job heartbeat target coverage retained a top shared unit-fast heap spike in the March 20, 2026 Linux Node 24 shard 1 rerun OOM lane."
+      },
+      {
+        "file": "src/config/schema.help.quality.test.ts",
+        "reason": "Schema help quality coverage retained the largest shared unit-fast heap spike in the March 20, 2026 Linux Node 24 shard 2 rerun OOM lane."
+      },
+      {
+        "file": "src/infra/run-node.test.ts",
+        "reason": "Run-node coverage retained a top shared unit-fast heap spike in the March 20, 2026 Linux Node 24 shard 2 rerun OOM lane."
+      },
+      {
+        "file": "src/media-understanding/providers/openai/audio.test.ts",
+        "reason": "OpenAI audio provider coverage retained a top shared unit-fast heap spike in the March 20, 2026 Linux Node 24 shard 2 rerun OOM lane."
+      },
+      {
+        "file": "src/media/fetch.telegram-network.test.ts",
+        "reason": "Telegram network fetch coverage retained a top shared unit-fast heap spike in the March 20, 2026 Linux Node 24 shard 2 rerun OOM lane."
+      },
+      {
+        "file": "src/channels/plugins/contracts/group-policy.contract.test.ts",
+        "reason": "Group policy contract coverage retained a top shared unit-fast heap spike in the March 20, 2026 Linux Node 24 shard 2 rerun OOM lane."
+      },
+      {
+        "file": "src/config/sessions/store.pruning.test.ts",
+        "reason": "Session store pruning coverage retained a top shared unit-fast heap spike in the March 20, 2026 Linux Node 24 shard 2 rerun OOM lane."
       }
     ],
     "threadSingleton": [