diff --git a/backend/src/routes/sessions.ts b/backend/src/routes/sessions.ts
index 4830c2c6..1338af53 100644
--- a/backend/src/routes/sessions.ts
+++ b/backend/src/routes/sessions.ts
@@ -77,9 +77,9 @@ export function sessionRoutes(
     return typeof runner.withPrincipal === "function" ? runner.withPrincipal(principal) : runner;
   };
 
-  const optionsWithRuntimeConfig = (runner: any, workspaceConfigPath: string | undefined, options: any) => (
+  const optionsWithRuntimeConfig = async (runner: any, workspaceConfigPath: string | undefined, options: any) => (
     workspaceConfigPath && typeof runner.acquireWorkspaceRuntime === "function"
-      ? { ...options, runtimeConfig: runner.acquireWorkspaceRuntime(workspaceConfigPath) }
+      ? { ...options, runtimeConfig: await runner.acquireWorkspaceRuntime(workspaceConfigPath) }
       : options
   );
 
@@ -431,7 +431,7 @@ export function sessionRoutes(
       let runtimeOptions = options;
       let rt: ReturnType<PiProcessManager["createFor"]> | undefined;
       try {
-        runtimeOptions = optionsWithRuntimeConfig(runner, workspaceConfigPath, options);
+        runtimeOptions = await optionsWithRuntimeConfig(runner, workspaceConfigPath, options);
         rt = d.mgr.createFor(id, runtimeOptions);
         bindRuntime(id, rt, runner, workspaceConfigPath);
       } catch (error) {
@@ -616,7 +616,7 @@ export function sessionRoutes(
           if (boundRuntimes.get(id) === current) boundRuntimes.delete(id);
           d.mgr.teardownIfCurrent(id, current);
         }
-        runtimeOptions = optionsWithRuntimeConfig(runner, workspaceConfigPath, options);
+        runtimeOptions = await optionsWithRuntimeConfig(runner, workspaceConfigPath, options);
         rt = d.mgr.createFor(id, runtimeOptions);
         bindRuntime(id, rt, runner, workspaceConfigPath);
       } catch {
diff --git a/backend/src/tht/tht-runner.ts b/backend/src/tht/tht-runner.ts
index e7841cd2..f395bd16 100644
--- a/backend/src/tht/tht-runner.ts
+++ b/backend/src/tht/tht-runner.ts
@@ -141,7 +141,7 @@ export class ThtRunner {
   }
 
   /** Render the pinned registry revision through the shared deterministic lease. */
-  acquireWorkspaceRuntime(workspaceConfigPath: string): RuntimeConfigLease {
+  async acquireWorkspaceRuntime(workspaceConfigPath: string): Promise<RuntimeConfigLease> {
     return this.runtimeConfigLeases().acquireSession(workspaceConfigPath);
   }
 
@@ -283,7 +283,7 @@ export class ThtRunner {
   static readonly DEFAULT_TIMEOUT_MS = 60_000;
   static readonly DWH_TIMEOUT_MS = 120_000;
 
-  run(
+  async run(
     args: string[], workspaceConfigPath?: string, timeoutMs: number = ThtRunner.DEFAULT_TIMEOUT_MS,
   ): Promise<{ code: number; stdout: string; stderr: string }> {
     if (
@@ -293,7 +293,7 @@ export class ThtRunner {
     ) {
       let runtime: RuntimeConfigLease;
       try {
-        runtime = this.acquireWorkspaceRuntime(workspaceConfigPath);
+        runtime = await this.acquireWorkspaceRuntime(workspaceConfigPath);
       } catch (error) {
         return Promise.reject(error);
       }
diff --git a/backend/src/workspaces/runtime-config-lease.ts b/backend/src/workspaces/runtime-config-lease.ts
index 5dd6fab4..d067a06c 100644
--- a/backend/src/workspaces/runtime-config-lease.ts
+++ b/backend/src/workspaces/runtime-config-lease.ts
@@ -1,11 +1,11 @@
 import { createHash } from "node:crypto";
-import { spawnSync } from "node:child_process";
+import { spawn } from "node:child_process";
 import { isIP } from "node:net";
 import { domainToASCII } from "node:url";
 import {
   existsSync, lstatSync, readFileSync,
 } from "node:fs";
-import { dirname, isAbsolute, join, relative, resolve } from "node:path";
+import { dirname, isAbsolute, join, relative, resolve, normalize } from "node:path";
 import { parseAllDocuments } from "yaml";
 import { resolveRuntimeBindings } from "./bindings.js";
 import {
@@ -53,6 +53,14 @@ interface SnapshotIdentity {
   descriptorDev: string;
   descriptorIno: string;
 }
+interface PublishedResponse {
+  path: string;
+  manifestPath: string;
+  manifest: string;
+  manifest_sha256: string;
+  dev: number;
+  ino: number;
+}
 interface PublishedIdentity {
   path: string;
   manifestPath: string;
@@ -142,28 +150,25 @@ export class WorkspaceRuntimeConfigLeaseFactory {
     } as RuntimeInstallationOverlay;
   }
 
-  acquireSession(snapshotPath: string): RuntimeConfigLease { return this.acquire(snapshotPath); }
-  acquireMaintenance(input: MaintenanceRuntimeInput): RuntimeConfigLease {
+  async acquireSession(snapshotPath: string): Promise<RuntimeConfigLease> { return this.acquire(snapshotPath); }
+  async acquireMaintenance(input: MaintenanceRuntimeInput): Promise<RuntimeConfigLease> {
     const snapshotPath = input.snapshotPath ?? input.workspaceConfigPath;
     if (!snapshotPath) throw new Error("maintenance runtime snapshot is required");
     return this.acquire(snapshotPath);
   }
 
-  private acquire(snapshotPath: string): RuntimeConfigLease {
-    const snapshot = this.readSnapshot(snapshotPath);
+  private async acquire(snapshotPath: string): Promise<RuntimeConfigLease> {
+    const snapshot = await this.readSnapshot(snapshotPath);
     const paths = this.runtimePaths(snapshot.workspaceId);
     const rendered = renderRuntimeConfig(snapshot.workspace, resolveRuntimeBindings(snapshot.workspace, this.env, this.secretRoots), paths, snapshot, this.installation, this.input.semanticRuntime ?? DEFAULT_SEMANTIC_RUNTIME);
     const renderedDigest = digest(rendered);
     const base = {
       workspace_id: snapshot.workspaceId, workspace_revision: snapshot.workspaceRevision,
-      descriptor_git_blob: snapshot.descriptorBlob!,
-      descriptor_sha256: snapshot.digest,
-      descriptor_dev: snapshot.descriptorDev,
-      descriptor_ino: snapshot.descriptorIno,
-      config_sha256: renderedDigest,
-      config_dwh_binding: this.computeBinding(rendered),
+      descriptor_git_blob: snapshot.descriptorBlob!, descriptor_sha256: snapshot.digest,
+      descriptor_dev: snapshot.descriptorDev, descriptor_ino: snapshot.descriptorIno,
+      config_sha256: renderedDigest, config_dwh_binding: await this.computeBinding(rendered),
     };
-    const result = this.publishSecure(snapshot.workspaceId, snapshot.workspaceRevision, rendered, base);
+    const result = await this.publishSecure(snapshot.workspaceId, snapshot.workspaceRevision, rendered, base);
     const identity: PublishedIdentity = {
       path: result.path, manifestPath: result.manifestPath, workspaceId: snapshot.workspaceId,
       workspaceRevision: snapshot.workspaceRevision, digest: renderedDigest, content: rendered,
@@ -172,41 +177,68 @@ export class WorkspaceRuntimeConfigLeaseFactory {
     return this.lease(identity);
   }
 
-  private helper(action: string, extra: Record<string, unknown>): any {
+  private async helper(action: string, extra: Record<string, unknown>): Promise<unknown> {
     const python = join(this.input.harnessDir, ".venv", "bin", "python");
     const modulePath = existsSync(join(this.input.harnessDir, "tht", "runtime_config_lease_io.py"))
       ? join(this.input.harnessDir, "tht", "runtime_config_lease_io.py")
       : join(process.cwd(), "../harness/tht/runtime_config_lease_io.py");
-    // Fixtures may provide a temporary harness directory; still execute the real
-    // project helper environment, never a fabricated TypeScript binding.
     const projectPython = join(dirname(dirname(modulePath)), ".venv", "bin", "python");
-    const executable = existsSync(python) ? python
-      : existsSync(projectPython) ? projectPython : (process.env.PYTHON ?? "python3");
+    const executable = existsSync(python) ? python : existsSync(projectPython) ? projectPython : (process.env.PYTHON ?? "python3");
     const helperArgs = existsSync(modulePath) ? [modulePath] : ["-m", "tht.runtime_config_lease_io"];
-    const result = spawnSync(executable, helperArgs, { cwd: this.input.harnessDir,
-      input: JSON.stringify({ action, ...extra }), encoding: "utf8",
-      env: { ...this.env, PYTHONPATH: [this.input.harnessDir, dirname(dirname(modulePath)), this.env.PYTHONPATH].filter(Boolean).join(":"), }, });
-    if (result.status !== 0) {
-      let detail = result.stderr?.trim() || result.stdout?.trim() || `runtime config ${action} failed`;
-      try { detail = JSON.parse(result.stdout).error ?? detail; } catch { /* preserve helper detail */ }
-      throw new Error(detail);
+    const env = { ...this.env };
+    // Never pass ambient capability variables to binding/snapshot/publication.
+    for (const key of Object.keys(env)) {
+      if ((key.startsWith("THT_RUNTIME_CONFIG_") && !["THT_RUNTIME_CONFIG_FSYNC_FAIL", "THT_RUNTIME_CONFIG_RENAME_FAIL"].includes(key)) || key.startsWith("THT_CONFIG_")) delete env[key];
     }
-    try { return JSON.parse(result.stdout); } catch { throw new Error(`runtime config ${action} returned invalid JSON`); }
+    env.PYTHONPATH = [this.input.harnessDir, dirname(dirname(modulePath)), env.PYTHONPATH].filter(Boolean).join(":");
+    const payload = JSON.stringify({ protocol_version: 1, action, ...extra });
+    const timeoutMs = 10_000;
+    return await new Promise((resolveResult, reject) => {
+      const child = spawn(executable, helperArgs, { cwd: this.input.harnessDir, env, detached: true, stdio: ["pipe", "pipe", "pipe"] });
+      let stdout = ""; let stderr = ""; let settled = false;
+      const finish = (error?: Error, value?: unknown) => { if (settled) return; settled = true; clearTimeout(timer); error ? reject(error) : resolveResult(value); };
+      const kill = () => { try { process.kill(-child.pid!, "SIGKILL"); } catch { try { child.kill("SIGKILL"); } catch { /* gone */ } } };
+      const timer = setTimeout(() => { kill(); finish(new Error(`runtime config ${action} timed out`)); }, timeoutMs);
+      const append = (target: "stdout" | "stderr", data: Buffer) => {
+        const next = target === "stdout" ? stdout + data.toString() : stderr + data.toString();
+        if (next.length > 16 * 1024 * 1024) { kill(); finish(new Error(`runtime config ${action} output exceeded limit`)); return; }
+        if (target === "stdout") stdout = next; else stderr = next;
+      };
+      child.stdout.on("data", (d: Buffer) => append("stdout", d)); child.stderr.on("data", (d: Buffer) => append("stderr", d));
+      child.on("error", (error) => finish(error));
+      child.on("close", (code) => {
+        if (code !== 0) { let detail = stderr.trim() || stdout.trim() || `runtime config ${action} failed`; try { detail = (JSON.parse(stdout) as {error?: string}).error ?? detail; } catch { /* preserve detail */ } finish(new Error(detail)); return; }
+        try { finish(undefined, JSON.parse(stdout)); } catch { finish(new Error(`runtime config ${action} returned invalid JSON`)); }
+      });
+      child.stdin.end(payload);
+    });
   }
 
-  private computeBinding(content: string): Record<string, string> {
-    try {
-      const value = this.helper("binding", { config_hex: Buffer.from(content).toString("hex") });
-      if (value && typeof value.workspace_id === "string" && typeof value.config_fingerprint === "string" && typeof value.input_fingerprint === "string") return value;
-      throw new Error("runtime config binding helper returned malformed output");
-    } catch (error) {
-      throw error instanceof Error ? error : new Error("runtime config binding failed");
-    }
+  private async computeBinding(content: string): Promise<Record<string, string>> {
+    const value = await this.helper("binding", { config_hex: Buffer.from(content).toString("hex") });
+    if (!value || typeof value !== "object" || Array.isArray(value) || Object.keys(value).sort().join(",") !== "config_fingerprint,input_fingerprint,workspace_id") throw new Error("runtime config binding helper returned malformed output");
+    const record = value as Record<string, unknown>;
+    if (Object.values(record).some((v) => typeof v !== "string")) throw new Error("runtime config binding helper returned malformed output");
+    return record as Record<string, string>;
   }
 
-  private publishSecure(workspaceId: string, revision: string, content: string, manifestBase: Record<string, unknown>): {path:string; manifestPath:string; manifest:string; manifest_sha256:string} {
-    return this.helper("publish", { data_root: this.input.dataRoot, workspace_id: workspaceId,
+  private async publishSecure(workspaceId: string, revision: string, content: string, manifestBase: Record<string, unknown>): Promise<PublishedResponse> {
+    const value = await this.helper("publish", { data_root: this.input.dataRoot, workspace_id: workspaceId,
       workspace_revision: revision, config_hex: Buffer.from(content).toString("hex"), manifest_base: manifestBase });
+    if (!value || typeof value !== "object" || Array.isArray(value)) throw new Error("runtime config publish helper returned malformed output");
+    const result = value as Record<string, unknown>;
+    if (Object.keys(result).sort().join(",") !== "dev,ino,manifest,manifestPath,manifest_sha256,path") throw new Error("runtime config publish helper returned malformed output");
+    let expectedRoot = resolve(this.input.dataRoot);
+    if (process.platform === "darwin" && (expectedRoot === "/var" || expectedRoot.startsWith("/var/") || expectedRoot === "/tmp" || expectedRoot.startsWith("/tmp/"))) expectedRoot = `/private${expectedRoot}`;
+    const expectedPath = join(expectedRoot, "sessions", workspaceId, "preprocessing", "runtime-config", `${revision}.yaml`);
+    const expectedManifestPath = join(expectedRoot, "sessions", workspaceId, "preprocessing", "runtime-config-manifests", `${revision}.json`);
+    if (result.path !== expectedPath || result.manifestPath !== expectedManifestPath
+      || typeof result.path !== "string" || !isAbsolute(result.path) || normalize(result.path) !== result.path
+      || typeof result.manifestPath !== "string" || !isAbsolute(result.manifestPath) || normalize(result.manifestPath) !== result.manifestPath
+      || result.workspace_id !== undefined || typeof result.manifest !== "string"
+      || typeof result.manifest_sha256 !== "string" || !/^[0-9a-f]{64}$/.test(result.manifest_sha256)
+      || typeof result.dev !== "number" || !Number.isSafeInteger(result.dev) || typeof result.ino !== "number" || !Number.isSafeInteger(result.ino)) throw new Error("runtime config publish helper returned malformed output");
+    return result as unknown as PublishedResponse;
   }
 
   private lease(identity: PublishedIdentity): RuntimeConfigLease {
@@ -225,7 +257,7 @@ export class WorkspaceRuntimeConfigLeaseFactory {
     if (!e.isDirectory() || e.isSymbolicLink() || e.nlink < 1 || (e.mode & 0o077) !== 0 || e.uid !== process.getuid?.()) throw new Error(`${label} is not trusted`);
   }
 
-  private readSnapshot(path: string): SnapshotIdentity {
+  private async readSnapshot(path: string): Promise<SnapshotIdentity> {
     if (!isAbsolute(path)) throw new Error("workspace snapshot path must be absolute");
     const root = resolve(this.input.runtimeSnapshotRoot);
     const rel = relative(root, path);
@@ -235,11 +267,14 @@ export class WorkspaceRuntimeConfigLeaseFactory {
     // production snapshot.json and descriptor component-by-component, and MUST prove
     // the Git commit/blob identity; a pathname-shaped file is never sufficient.
     const repositoryRoot = join(dirname(root), "repo");
-    const verified = this.helper("verified-snapshot", {
+    const verified = await this.helper("verified-snapshot", {
       snapshots_root: root, repository_root: repositoryRoot,
       workspace_revision: match[1], workspace_id: match[2],
-    });
-    if (!verified || typeof verified.source !== "string" || typeof verified.git_source !== "string"
+    }) as Record<string, unknown>;
+    const verifiedKeys = ["descriptor_dev", "descriptor_git_blob", "descriptor_ino", "git_source", "sha256", "snapshot_path", "source", "workspace_id", "workspace_revision"];
+    if (Object.keys(verified).sort().join(",") !== verifiedKeys.join(",")
+      || verified.workspace_id !== match[2] || verified.workspace_revision !== match[1]
+      || typeof verified.source !== "string" || typeof verified.git_source !== "string"
       || verified.sha256 !== digest(verified.source) || verified.snapshot_path !== path
       || !/^\d+$/.test(String(verified.descriptor_dev)) || !/^\d+$/.test(String(verified.descriptor_ino))) {
       throw new Error("workspace snapshot integrity check failed");
diff --git a/backend/test/workspace-runtime-config-lease.test.ts b/backend/test/workspace-runtime-config-lease.test.ts
index b054a1b9..cfb0ef13 100644
--- a/backend/test/workspace-runtime-config-lease.test.ts
+++ b/backend/test/workspace-runtime-config-lease.test.ts
@@ -84,11 +84,11 @@ function fixture(extraEnv: Record<string, string> = {}) {
   return { root, repo, snapshotPath, factory, factoryInput, canonicalDescriptor, snapshotManifest: join(snapshotsDir, "snapshot.json") };
 }
 
-test("session and maintenance share deterministic bytes and path", () => {
+test("session and maintenance share deterministic bytes and path", async () => {
   const f = fixture();
   try {
-    const session = f.factory.acquireSession(f.snapshotPath);
-    const maintenance = f.factory.acquireMaintenance({ snapshotPath: f.snapshotPath });
+    const session = await f.factory.acquireSession(f.snapshotPath);
+    const maintenance = await f.factory.acquireMaintenance({ snapshotPath: f.snapshotPath });
     expect(session.path).toBe(maintenance.path);
     expect(readFileSync(session.path, "utf8")).toBe(readFileSync(maintenance.path, "utf8"));
     expect(lstatSync(session.path).mode & 0o777).toBe(0o400);
@@ -101,19 +101,19 @@ test("session and maintenance share deterministic bytes and path", () => {
   } finally { rmSync(f.root, { recursive: true, force: true }); }
 });
 
-test("same revision changed bytes are refused", () => {
+test("same revision changed bytes are refused", async () => {
   const f = fixture();
   try {
-    const first = f.factory.acquireSession(f.snapshotPath);
+    const first = await f.factory.acquireSession(f.snapshotPath);
     chmodSync(first.path, 0o600);
     writeFileSync(first.path, "changed", { mode: 0o600 });
     chmodSync(first.path, 0o400);
-    expect(() => f.factory.acquireSession(f.snapshotPath)).toThrow(/changed|mismatch|trusted/i);
+    await expect(f.factory.acquireSession(f.snapshotPath)).rejects.toThrow(/changed|mismatch|trusted/i);
     first.release();
   } finally { rmSync(f.root, { recursive: true, force: true }); }
 });
 
-test("snapshot descriptor must equal the Git canonical descriptor", () => {
+test("snapshot descriptor must equal the Git canonical descriptor", async () => {
   const f = fixture();
   try {
     const mutated = f.canonicalDescriptor.replace("database: analytics", "database: evil").replace("name: Lease", "name: Lease analytics");
@@ -126,29 +126,29 @@ test("snapshot descriptor must equal the Git canonical descriptor", () => {
     chmodSync(manifestPath, 0o600);
     writeFileSync(manifestPath, JSON.stringify(manifest), { mode: 0o600 });
     chmodSync(manifestPath, 0o400);
-    expect(() => f.factory.acquireSession(f.snapshotPath)).toThrow(/Git descriptor|integrity|identity/i);
+    await expect(f.factory.acquireSession(f.snapshotPath)).rejects.toThrow(/Git descriptor|integrity|identity/i);
   } finally { rmSync(f.root, { recursive: true, force: true }); }
 });
 
-test("same-byte replacement of the registry descriptor is refused", () => {
+test("same-byte replacement of the registry descriptor is refused", async () => {
   const f = fixture();
   try {
-    const first = f.factory.acquireSession(f.snapshotPath);
+    const first = await f.factory.acquireSession(f.snapshotPath);
     const replacement = `${f.snapshotPath}.replacement`;
     writeFileSync(replacement, readFileSync(f.snapshotPath), { mode: 0o400 });
     chmodSync(f.snapshotPath, 0o600);
     rmSync(f.snapshotPath);
     writeFileSync(f.snapshotPath, readFileSync(replacement), { mode: 0o400 });
-    expect(() => f.factory.acquireSession(f.snapshotPath)).toThrow(/identity|changed|mismatch|trusted/i);
+    await expect(f.factory.acquireSession(f.snapshotPath)).rejects.toThrow(/identity|changed|mismatch|trusted/i);
     first.release();
   } finally { rmSync(f.root, { recursive: true, force: true }); }
 });
 
 
-test("manifest binds the complete canonical destination directory chain", () => {
+test("manifest binds the complete canonical destination directory chain", async () => {
   const f = fixture();
   try {
-    const lease = f.factory.acquireSession(f.snapshotPath);
+    const lease = await f.factory.acquireSession(f.snapshotPath);
     const manifest = JSON.parse(readFileSync(lease.manifestPath, "utf8"));
     expect(manifest.directory_identities.length).toBeGreaterThan(5);
     expect(manifest.directory_identities.map((entry: { path: string }) => entry.path)).toContain(
@@ -160,7 +160,7 @@ test("manifest binds the complete canonical destination directory chain", () =>
   } finally { rmSync(f.root, { recursive: true, force: true }); }
 });
 
-test("raw Git identity ignores replacement refs", () => {
+test("raw Git identity ignores replacement refs", async () => {
   const f = fixture();
   try {
     const evil = f.canonicalDescriptor.replace("database: analytics", "database: evil");
@@ -179,14 +179,14 @@ test("raw Git identity ignores replacement refs", () => {
     chmodSync(f.snapshotManifest, 0o600);
     writeFileSync(f.snapshotManifest, JSON.stringify(snapshot));
     chmodSync(f.snapshotManifest, 0o400);
-    expect(() => f.factory.acquireSession(f.snapshotPath)).toThrow(/Git descriptor|integrity|identity/i);
+    await expect(f.factory.acquireSession(f.snapshotPath)).rejects.toThrow(/Git descriptor|integrity|identity/i);
   } finally { rmSync(f.root, { recursive: true, force: true }); }
 });
 
-test("replacement of canonical destination directories is refused", () => {
+test("replacement of canonical destination directories is refused", async () => {
   const f = fixture();
   try {
-    const lease = f.factory.acquireSession(f.snapshotPath);
+    const lease = await f.factory.acquireSession(f.snapshotPath);
     const original = join(f.root, "data", "sessions", workspace);
     const moved = `${original}.moved`;
     renameSync(original, moved);
@@ -194,14 +194,14 @@ test("replacement of canonical destination directories is refused", () => {
     mkdirSync(join(original, "preprocessing", "runtime-config-manifests"), { recursive: true, mode: 0o700 });
     renameSync(join(moved, "preprocessing", "runtime-config", `${lease.workspaceRevision}.yaml`), join(original, "preprocessing", "runtime-config", `${lease.workspaceRevision}.yaml`));
     renameSync(join(moved, "preprocessing", "runtime-config-manifests", `${lease.workspaceRevision}.json`), join(original, "preprocessing", "runtime-config-manifests", `${lease.workspaceRevision}.json`));
-    expect(() => f.factory.acquireSession(f.snapshotPath)).toThrow(/changed|mismatch|same-revision|identity|trusted/i);
+    await expect(f.factory.acquireSession(f.snapshotPath)).rejects.toThrow(/changed|mismatch|same-revision|identity|trusted/i);
   } finally { rmSync(f.root, { recursive: true, force: true }); }
 });
 
-test("rename faults fail closed and remove staging files", () => {
+test("rename faults fail closed and remove staging files", async () => {
   const f = fixture({ THT_RUNTIME_CONFIG_RENAME_FAIL: "1" });
   try {
-    expect(() => f.factory.acquireSession(f.snapshotPath)).toThrow(/rename|failed/i);
+    await expect(f.factory.acquireSession(f.snapshotPath)).rejects.toThrow(/rename|failed/i);
     const runtime = join(f.root, "data", "sessions", workspace, "preprocessing");
     for (const dir of ["runtime-config", "runtime-config-manifests"]) {
       if (existsSync(join(runtime, dir))) expect(readdirSync(join(runtime, dir)).filter((name) => name.includes("staging")).length).toBe(0);
@@ -210,11 +210,11 @@ test("rename faults fail closed and remove staging files", () => {
 });
 
 
-test("session and operator outputs retain normalized private-host policy and binding", () => {
+test("session and operator outputs retain normalized private-host policy and binding", async () => {
   const f = fixture({ THT_HTTP_PRIVATE_HOST_ALLOWLIST: "internal.example,warehouse.example" });
   try {
-    const session = f.factory.acquireSession(f.snapshotPath);
-    const maintenance = f.factory.acquireMaintenance({ snapshotPath: f.snapshotPath });
+    const session = await f.factory.acquireSession(f.snapshotPath);
+    const maintenance = await f.factory.acquireMaintenance({ snapshotPath: f.snapshotPath });
     const output = readFileSync(session.path, "utf8");
     expect(output).toContain("http_private_host_allowlist");
     expect(output).toContain("- internal.example");
@@ -228,29 +228,29 @@ test("session and operator outputs retain normalized private-host policy and bin
 });
 
 
-test("unexpected manifest fields are refused before handoff", () => {
+test("unexpected manifest fields are refused before handoff", async () => {
   const f = fixture();
   try {
-    const lease = f.factory.acquireSession(f.snapshotPath);
+    const lease = await f.factory.acquireSession(f.snapshotPath);
     const manifest = JSON.parse(readFileSync(lease.manifestPath, "utf8"));
     manifest.unexpected = true;
     chmodSync(lease.manifestPath, 0o600);
     writeFileSync(lease.manifestPath, JSON.stringify(manifest));
-    expect(() => f.factory.acquireSession(f.snapshotPath)).toThrow(/manifest|invalid|changed/i);
+    await expect(f.factory.acquireSession(f.snapshotPath)).rejects.toThrow(/manifest|invalid|changed/i);
   } finally { rmSync(f.root, { recursive: true, force: true }); }
 });
 
-test("runtime config symlink replacement is refused", () => {
+test("runtime config symlink replacement is refused", async () => {
   const f = fixture();
   try {
-    const lease = f.factory.acquireSession(f.snapshotPath);
+    const lease = await f.factory.acquireSession(f.snapshotPath);
     const replacement = `${lease.path}.real`;
     writeFileSync(replacement, readFileSync(lease.path), { mode: 0o400 });
     chmodSync(lease.path, 0o600);
     rmSync(lease.path);
     // A no-follow handoff must never consume this pathname.
     execFileSync("ln", ["-s", replacement, lease.path]);
-    expect(() => f.factory.acquireSession(f.snapshotPath)).toThrow(/trusted|changed|configuration|symbolic/i);
+    await expect(f.factory.acquireSession(f.snapshotPath)).rejects.toThrow(/trusted|changed|configuration|symbolic/i);
   } finally { rmSync(f.root, { recursive: true, force: true }); }
 });
 
@@ -260,11 +260,11 @@ function realHarnessBinding(config: string): Record<string, string> {
   const python = join(process.cwd(), "..", "harness", ".venv", "bin", "python");
   return JSON.parse(execFileSync(python, [helper], {
     cwd: join(process.cwd(), "..", "harness"), encoding: "utf8",
-    input: JSON.stringify({ action: "binding", config_hex: Buffer.from(config).toString("hex") }),
+    input: JSON.stringify({ protocol_version: 1, action: "binding", config_hex: Buffer.from(config).toString("hex") }),
   }));
 }
 
-test("explicit installation overlay is canonical and has one real harness binding", () => {
+test("explicit installation overlay is canonical and has one real harness binding", async () => {
   const f = fixture();
   const overlay = {
     profile: "workstation",
@@ -277,8 +277,8 @@ test("explicit installation overlay is canonical and has one real harness bindin
   const sessionFactory = new WorkspaceRuntimeConfigLeaseFactory({ ...f.factoryInput, installationOverlay: overlay });
   const maintenanceFactory = new WorkspaceRuntimeConfigLeaseFactory({ ...f.factoryInput, installationOverlay: overlay });
   try {
-    const session = sessionFactory.acquireSession(f.snapshotPath);
-    const maintenance = maintenanceFactory.acquireMaintenance({ workspaceConfigPath: f.snapshotPath });
+    const session = await sessionFactory.acquireSession(f.snapshotPath);
+    const maintenance = await maintenanceFactory.acquireMaintenance({ workspaceConfigPath: f.snapshotPath });
     const sessionYaml = readFileSync(session.path, "utf8");
     const maintenanceYaml = readFileSync(maintenance.path, "utf8");
     expect(session.path).toBe(maintenance.path);
@@ -298,10 +298,10 @@ test("explicit installation overlay is canonical and has one real harness bindin
 test.each([
   ["config-file", "config-file"], ["config-parent", "config-parent"],
   ["manifest-file", "manifest-file"], ["manifest-parent", "manifest-parent"],
-] as const)("fsync fault at %s fails closed and retries to the same durable pair", (_label, stage) => {
+] as const)("fsync fault at %s fails closed and retries to the same durable pair", async (_label, stage) => {
   const f = fixture({ THT_RUNTIME_CONFIG_FSYNC_FAIL: stage });
   try {
-    expect(() => f.factory.acquireSession(f.snapshotPath)).toThrow(/fsync|failed/i);
+    await expect(f.factory.acquireSession(f.snapshotPath)).rejects.toThrow(/fsync|failed/i);
     const runtime = join(f.root, "data", "sessions", workspace, "preprocessing");
     for (const dir of ["runtime-config", "runtime-config-manifests"]) {
       if (existsSync(join(runtime, dir))) {
@@ -311,7 +311,7 @@ test.each([
     const recovered = new WorkspaceRuntimeConfigLeaseFactory({ ...f.factoryInput, env: {
       ...f.factoryInput.env, THT_RUNTIME_CONFIG_FSYNC_FAIL: undefined,
     } });
-    const lease = recovered.acquireSession(f.snapshotPath);
+    const lease = await recovered.acquireSession(f.snapshotPath);
     expect(existsSync(lease.path)).toBe(true);
     expect(existsSync(lease.manifestPath)).toBe(true);
     expect(JSON.parse(readFileSync(lease.manifestPath, "utf8")).config_sha256)
@@ -324,10 +324,10 @@ for (const [label, mutate] of [
   ["outside path", (f: ReturnType<typeof fixture>) => join(f.root, "outside.yaml")],
   ["wrong workspace id", (f: ReturnType<typeof fixture>) => f.snapshotPath.replace("abc.yaml", "abd.yaml")],
 ] as const) {
-  test(`rejects ${label} before publication`, () => {
+  test(`rejects ${label} before publication`, async () => {
     const f = fixture();
     try {
-      expect(() => f.factory.acquireSession(mutate(f))).toThrow(/trusted|snapshot|identity|path|Git|unavailable|ENOENT|No such/i);
+      await expect(f.factory.acquireSession(mutate(f))).rejects.toThrow(/trusted|snapshot|identity|path|Git|unavailable|ENOENT|No such/i);
     } finally { rmSync(f.root, { recursive: true, force: true }); }
   });
 }
@@ -336,11 +336,11 @@ for (const [label, replace] of [
   ["descriptor symlink", (path: string, root: string) => { const target = `${path}.target`; writeFileSync(target, readFileSync(path), { mode: 0o400 }); rmSync(path); execFileSync("ln", ["-s", target, path]); }],
   ["descriptor hardlink", (path: string, root: string) => { const target = `${path}.target`; execFileSync("ln", [path, target]); rmSync(path); execFileSync("ln", [target, path]); }],
 ] as const) {
-  test(`rejects ${label}`, () => {
+  test(`rejects ${label}`, async () => {
     const f = fixture();
     try {
       replace(f.snapshotPath, f.root);
-      expect(() => f.factory.acquireSession(f.snapshotPath)).toThrow(/trusted|integrity|identity|link/i);
+      await expect(f.factory.acquireSession(f.snapshotPath)).rejects.toThrow(/trusted|integrity|identity|link/i);
     } finally { rmSync(f.root, { recursive: true, force: true }); }
   });
 }
@@ -349,23 +349,23 @@ for (const [label, target] of [
   ["config symlink", "config"], ["config hardlink", "config"],
   ["manifest symlink", "manifest"], ["manifest hardlink", "manifest"],
 ] as const) {
-  test(`rejects destination ${label} and recovers safely`, () => {
+  test(`rejects destination ${label} and recovers safely`, async () => {
     const f = fixture();
     try {
-      const first = f.factory.acquireSession(f.snapshotPath);
+      const first = await f.factory.acquireSession(f.snapshotPath);
       const path = target === "config" ? first.path : first.manifestPath;
       const backup = `${path}.target`;
       writeFileSync(backup, readFileSync(path), { mode: target === "config" ? 0o400 : 0o600 });
       rmSync(path);
       if (label.includes("symlink")) execFileSync("ln", ["-s", backup, path]);
       else execFileSync("ln", [backup, path]);
-      expect(() => f.factory.acquireSession(f.snapshotPath)).toThrow(/trusted|configuration|manifest|link|changed/i);
+      await expect(f.factory.acquireSession(f.snapshotPath)).rejects.toThrow(/trusted|configuration|manifest|link|changed/i);
       rmSync(path);
       // A replaced inode can never be trusted again. Remove the paired durable
       // publication and let a fresh no-replace publication recover the layout.
       rmSync(first.path, { force: true });
       rmSync(first.manifestPath, { force: true });
-      const recovered = f.factory.acquireSession(f.snapshotPath);
+      const recovered = await f.factory.acquireSession(f.snapshotPath);
       expect(recovered.path).toBe(first.path);
     } finally { rmSync(f.root, { recursive: true, force: true }); }
   });
@@ -374,44 +374,44 @@ for (const [label, target] of [
 for (const [label, target, mode] of [
   ["config", "config", 0o600], ["manifest", "manifest", 0o400],
 ] as const) {
-  test(`refuses wrong ${label} mode then recovers after restoring mode`, () => {
+  test(`refuses wrong ${label} mode then recovers after restoring mode`, async () => {
     const f = fixture();
     try {
-      const first = f.factory.acquireSession(f.snapshotPath);
+      const first = await f.factory.acquireSession(f.snapshotPath);
       const path = target === "config" ? first.path : first.manifestPath;
       chmodSync(path, mode);
-      expect(() => f.factory.acquireSession(f.snapshotPath)).toThrow(/trusted|mode|configuration|manifest/i);
+      await expect(f.factory.acquireSession(f.snapshotPath)).rejects.toThrow(/trusted|mode|configuration|manifest/i);
       chmodSync(path, target === "config" ? 0o400 : 0o600);
-      expect(() => f.factory.acquireSession(f.snapshotPath)).not.toThrow();
+      await expect(f.factory.acquireSession(f.snapshotPath)).resolves.toBeDefined();
     } finally { rmSync(f.root, { recursive: true, force: true }); }
   });
 }
 
- test("release retains durable state while changed binding is refused by a new factory", () => {
+ test("release retains durable state while changed binding is refused by a new factory", async () => {
   const f = fixture();
   try {
-    const first = f.factory.acquireSession(f.snapshotPath);
+    const first = await f.factory.acquireSession(f.snapshotPath);
     first.release();
     const changed = new WorkspaceRuntimeConfigLeaseFactory({ ...f.factoryInput, env: {
       ...f.factoryInput.env, THT_WS_ABC_DWH_HOST: "other-dwh",
     } });
-    expect(() => changed.acquireSession(f.snapshotPath)).toThrow(/changed|mismatch|configuration/i);
+    await expect(changed.acquireSession(f.snapshotPath)).rejects.toThrow(/changed|mismatch|configuration/i);
     expect(existsSync(first.path)).toBe(true);
   } finally { rmSync(f.root, { recursive: true, force: true }); }
 });
 
-test("strict manifest rejects an extra field and recovery preserves exact bytes", () => {
+test("strict manifest rejects an extra field and recovery preserves exact bytes", async () => {
   const f = fixture();
   try {
-    const first = f.factory.acquireSession(f.snapshotPath);
+    const first = await f.factory.acquireSession(f.snapshotPath);
     const original = readFileSync(first.manifestPath, "utf8");
     const manifest = JSON.parse(original);
     manifest.extra = "reject";
     chmodSync(first.manifestPath, 0o600);
     writeFileSync(first.manifestPath, JSON.stringify(manifest), { mode: 0o600 });
-    expect(() => f.factory.acquireSession(f.snapshotPath)).toThrow(/manifest|invalid|changed/i);
+    await expect(f.factory.acquireSession(f.snapshotPath)).rejects.toThrow(/manifest|invalid|changed/i);
     writeFileSync(first.manifestPath, original, { mode: 0o600 });
-    expect(() => f.factory.acquireSession(f.snapshotPath)).not.toThrow();
+    await expect(f.factory.acquireSession(f.snapshotPath)).resolves.toBeDefined();
   } finally { rmSync(f.root, { recursive: true, force: true }); }
 });
 
@@ -420,40 +420,40 @@ test.each([
   ["duplicate", "alpha.example,alpha.example"],
   ["uppercase", "Alpha.example"],
   ["ip address", "127.0.0.1"],
-] as const)("rejects %s private-host policy", (_label, allowlist) => {
+] as const)("rejects %s private-host policy", async (_label, allowlist) => {
   expect(() => fixture({ THT_HTTP_PRIVATE_HOST_ALLOWLIST: allowlist }))
     .toThrow(/allowlist|hostname|duplicate|invalid/i);
 });
 
 test.each([
   ["runtime-config", "config"], ["runtime-config-manifests", "manifest"],
-] as const)("rejects a replaced %s destination ancestor", (directory, _kind) => {
+] as const)("rejects a replaced %s destination ancestor", async (directory, _kind) => {
   const f = fixture();
   try {
-    const lease = f.factory.acquireSession(f.snapshotPath);
+    const lease = await f.factory.acquireSession(f.snapshotPath);
     const parent = join(f.root, "data", "sessions", workspace, "preprocessing", directory);
     const moved = `${parent}.moved`;
     renameSync(parent, moved);
     execFileSync("ln", ["-s", moved, parent]);
-    expect(() => f.factory.acquireSession(f.snapshotPath)).toThrow(/trusted|symbolic|changed|directory/i);
+    await expect(f.factory.acquireSession(f.snapshotPath)).rejects.toThrow(/trusted|symbolic|changed|directory/i);
     rmSync(parent);
     renameSync(moved, parent);
-    expect(() => f.factory.acquireSession(f.snapshotPath)).not.toThrow();
+    await expect(f.factory.acquireSession(f.snapshotPath)).resolves.toBeDefined();
     lease.release();
   } finally { rmSync(f.root, { recursive: true, force: true }); }
 });
 
-test("release is idempotent and does not remove either durable publication", () => {
+test("release is idempotent and does not remove either durable publication", async () => {
   const f = fixture();
   try {
-    const lease = f.factory.acquireSession(f.snapshotPath);
+    const lease = await f.factory.acquireSession(f.snapshotPath);
     lease.release(); lease.release();
     expect(existsSync(lease.path)).toBe(true);
     expect(existsSync(lease.manifestPath)).toBe(true);
   } finally { rmSync(f.root, { recursive: true, force: true }); }
 });
 
-test("partial os.write calls are completed by the real Python publication helper", () => {
+test("partial os.write calls are completed by the real Python publication helper", async () => {
   const python = join(process.cwd(), "..", "harness", ".venv", "bin", "python");
   const helper = join(process.cwd(), "..", "harness", "tht", "runtime_config_lease_io.py");
   const code = `import os, sys; sys.path.insert(0, ${JSON.stringify(dirname(helper))}); import runtime_config_lease_io as m; real=os.write; os.write=lambda fd,b: real(fd,b[:3]); m.write_all(1, b'partial-write-ok\\n')`;
@@ -461,20 +461,20 @@ test("partial os.write calls are completed by the real Python publication helper
   expect(output).toBe("partial-write-ok\n");
 });
 
-test("a clean existing equal publication is reconciled by a new factory", () => {
+test("a clean existing equal publication is reconciled by a new factory", async () => {
   const f = fixture();
   try {
-    const first = f.factory.acquireSession(f.snapshotPath);
-    const second = new WorkspaceRuntimeConfigLeaseFactory(f.factoryInput).acquireMaintenance({ snapshotPath: f.snapshotPath });
+    const first = await f.factory.acquireSession(f.snapshotPath);
+    const second = await new WorkspaceRuntimeConfigLeaseFactory(f.factoryInput).acquireMaintenance({ snapshotPath: f.snapshotPath });
     expect(readFileSync(second.path)).toEqual(readFileSync(first.path));
     expect(readFileSync(second.manifestPath)).toEqual(readFileSync(first.manifestPath));
   } finally { rmSync(f.root, { recursive: true, force: true }); }
 });
 
-test.each([["config"], ["manifest"]] as const)("rename failure is scoped to the %s branch and leaves no staging", (kind) => {
+test.each([["config"], ["manifest"]] as const)("rename failure is scoped to the %s branch and leaves no staging", async (kind) => {
   const f = fixture({ THT_RUNTIME_CONFIG_RENAME_FAIL: kind });
   try {
-    expect(() => f.factory.acquireSession(f.snapshotPath)).toThrow(/rename|failed/i);
+    await expect(f.factory.acquireSession(f.snapshotPath)).rejects.toThrow(/rename|failed/i);
     const runtime = join(f.root, "data", "sessions", workspace, "preprocessing");
     for (const dir of ["runtime-config", "runtime-config-manifests"]) {
       if (existsSync(join(runtime, dir))) expect(readdirSync(join(runtime, dir)).some((name) => name.includes("staging"))).toBe(false);
@@ -482,7 +482,7 @@ test.each([["config"], ["manifest"]] as const)("rename failure is scoped to the
   } finally { rmSync(f.root, { recursive: true, force: true }); }
 });
 
-test("snapshot manifest rejects an undeclared extra immutable file", () => {
+test("snapshot manifest rejects an undeclared extra immutable file", async () => {
   const f = fixture();
   try {
     const snapshot = JSON.parse(readFileSync(f.snapshotManifest, "utf8"));
@@ -490,15 +490,15 @@ test("snapshot manifest rejects an undeclared extra immutable file", () => {
     snapshot.files["smuggled.txt"] = createHash("sha256").update("smuggled").digest("hex");
     chmodSync(f.snapshotManifest, 0o600);
     writeFileSync(f.snapshotManifest, JSON.stringify(snapshot), { mode: 0o400 });
-    expect(() => f.factory.acquireSession(f.snapshotPath)).toThrow(/integrity|snapshot|trusted/i);
+    await expect(f.factory.acquireSession(f.snapshotPath)).rejects.toThrow(/integrity|snapshot|trusted/i);
   } finally { rmSync(f.root, { recursive: true, force: true }); }
 });
 
 
-test("independent OS publishers converge when equal and elect one winner when unequal", () => {
+test("independent OS publishers converge when equal and elect one winner when unequal", async () => {
   const f = fixture();
   try {
-    const seed = f.factory.acquireSession(f.snapshotPath);
+    const seed = await f.factory.acquireSession(f.snapshotPath);
     const full = JSON.parse(readFileSync(seed.manifestPath, "utf8"));
     const base = Object.fromEntries(["workspace_id", "workspace_revision", "descriptor_git_blob",
       "descriptor_sha256", "descriptor_dev", "descriptor_ino", "config_dwh_binding"]
@@ -509,7 +509,7 @@ test("independent OS publishers converge when equal and elect one winner when un
     // Leave the workspace-owned destination directories in place, but remove
     // both durable leaves: the following OS processes race on a clean layout.
     rmSync(seed.path); rmSync(seed.manifestPath);
-    const payload = JSON.stringify({ action: "publish", data_root: f.factoryInput.dataRoot,
+    const payload = JSON.stringify({ protocol_version: 1, action: "publish", data_root: f.factoryInput.dataRoot,
       workspace_id: workspace, workspace_revision: full.workspace_revision,
       config_hex: Buffer.from(configBytes).toString("hex"), manifest_base: base });
     const code = `import json,multiprocessing,sys
@@ -538,10 +538,10 @@ print(json.dumps([q.exitcode for q in p]))`
 });
 
 
-test.each(["leaf", "ancestor"] as const)("actual harness rejects canonical %s swap", (kind) => {
+test.each(["leaf", "ancestor"] as const)("actual harness rejects canonical %s swap", async (kind) => {
   const f = fixture();
   try {
-    const lease = f.factory.acquireSession(f.snapshotPath);
+    const lease = await f.factory.acquireSession(f.snapshotPath);
     const harnessBin = join(process.cwd(), "..", "harness", ".venv", "bin", "tht");
     const harnessCwd = join(process.cwd(), "..", "harness");
     const env = { ...process.env, THT_RUNTIME_CONFIG_MANIFEST_SHA256: lease.manifestSha256 };
@@ -562,10 +562,10 @@ test.each(["leaf", "ancestor"] as const)("actual harness rejects canonical %s sw
 });
 
 
-test("actual harness rejects a workspace chain swap between config and manifest traversal", () => {
+test("actual harness rejects a workspace chain swap between config and manifest traversal", async () => {
   const f = fixture();
   try {
-    const lease = f.factory.acquireSession(f.snapshotPath);
+    const lease = await f.factory.acquireSession(f.snapshotPath);
     const python = join(process.cwd(), "..", "harness", ".venv", "bin", "python");
     const helper = join(process.cwd(), "..", "harness", "tht");
     const workspaceRoot = join(f.factoryInput.dataRoot, "sessions", workspace);
diff --git a/backend/test/workspace-runtime-handoff.test.ts b/backend/test/workspace-runtime-handoff.test.ts
index b407c651..24c74c4e 100644
--- a/backend/test/workspace-runtime-handoff.test.ts
+++ b/backend/test/workspace-runtime-handoff.test.ts
@@ -169,8 +169,8 @@ test("real schema-v3 registry revision loads through ThtRunner and the harness c
 test("separate runtime leases hand off byte-identical revision Evidence configs accepted by tht", async () => {
   const f = await fixture();
   const runner = runnerFor(f);
-  const first = runner.acquireWorkspaceRuntime(f.revision.snapshotPath);
-  const second = runner.acquireWorkspaceRuntime(f.revision.snapshotPath);
+  const first = await runner.acquireWorkspaceRuntime(f.revision.snapshotPath);
+  const second = await runner.acquireWorkspaceRuntime(f.revision.snapshotPath);
   const expectedRoot = join(
     f.registryConfig.root,
     "snapshots",
@@ -226,7 +226,7 @@ test("separate runtime leases hand off byte-identical revision Evidence configs
 test("real Evidence-content-only commit changes runtime identity and root with identical descriptor YAML", async () => {
   const f = await fixture();
   const runner = runnerFor(f);
-  const first = runner.acquireWorkspaceRuntime(f.revision.snapshotPath);
+  const first = await runner.acquireWorkspaceRuntime(f.revision.snapshotPath);
   const descriptorBefore = readFileSync(f.revision.snapshotPath, "utf8");
   writeFileSync(
     join(f.source, "workspace-content", "psd-clinical", "evidence", "guide.md"),
@@ -237,7 +237,7 @@ test("real Evidence-content-only commit changes runtime identity and root with i
   await git(f.source, ["push", "origin", "main"]);
   await f.registry.pull();
   const current = (await f.registry.list())[0];
-  const second = runner.acquireWorkspaceRuntime(current.snapshotPath);
+  const second = await runner.acquireWorkspaceRuntime(current.snapshotPath);
 
   try {
     expect(current.commit).not.toBe(f.revision.commit);
@@ -281,7 +281,7 @@ test("signed HTTP Evidence resolves its file binding and config check never capt
     max_cache_bytes: 67890
 `));
   const runner = runnerFor(f);
-  const lease = runner.acquireWorkspaceRuntime(f.revision.snapshotPath);
+  const lease = await runner.acquireWorkspaceRuntime(f.revision.snapshotPath);
   try {
     const yaml = readFileSync(lease.path, "utf8");
     expect(parse(yaml).evidence.sources).toEqual([{
@@ -325,7 +325,7 @@ test("static S3 Evidence resolves only configured secret-root file paths", async
     retain_published_generations: 7
 `));
   const runner = runnerFor(f);
-  const lease = runner.acquireWorkspaceRuntime(f.revision.snapshotPath);
+  const lease = await runner.acquireWorkspaceRuntime(f.revision.snapshotPath);
   try {
     const yaml = readFileSync(lease.path, "utf8");
     expect(parse(yaml).evidence.sources).toEqual([{
diff --git a/harness/tests/test_runtime_config_lease_io.py b/harness/tests/test_runtime_config_lease_io.py
new file mode 100644
index 00000000..8170f277
--- /dev/null
+++ b/harness/tests/test_runtime_config_lease_io.py
@@ -0,0 +1,84 @@
+"""Focused unit coverage for the privileged runtime publication seam."""
+
+import os
+
+import pytest
+
+from tht import runtime_config_lease_io as lease_io
+
+
+def _manifest() -> dict:
+    return {
+        "version": 1, "workspace_id": "abc", "workspace_revision": "a" * 40,
+        "descriptor_git_blob": "b" * 40, "descriptor_sha256": "c" * 64,
+        "descriptor_dev": "1", "descriptor_ino": "2", "config_sha256": "d" * 64,
+        "config_dwh_binding": {
+            "workspace_id": "abc", "config_fingerprint": "e", "input_fingerprint": "f"
+        },
+        "config_dev": "1", "config_ino": "3", "config_size": "4",
+        "config_mode": "400", "config_uid": str(os.getuid()), "config_nlink": "1",
+        "directory_identities": [{"path": "/", "dev": "1", "ino": "1", "mode": "755", "uid": "0"}],
+    }
+
+
+def test_strict_manifest_rejects_unknown_or_missing_fields():
+    value = _manifest()
+    assert lease_io.strict_manifest(value) is value
+    with pytest.raises(RuntimeError):
+        lease_io.strict_manifest({**value, "unexpected": True})
+    missing = dict(value)
+    del missing["config_sha256"]
+    with pytest.raises(RuntimeError):
+        lease_io.strict_manifest(missing)
+
+
+def test_private_alias_is_darwin_only(monkeypatch):
+    monkeypatch.setattr(lease_io.sys, "platform", "linux")
+    assert lease_io._canonical_root("/tmp/runtime") == "/tmp/runtime"
+    assert lease_io._canonical_root("/var/lib/runtime") == "/var/lib/runtime"
+    monkeypatch.setattr(lease_io.sys, "platform", "darwin")
+    assert lease_io._canonical_root("/tmp/runtime") == "/private/tmp/runtime"
+    assert lease_io._canonical_root("/var/lib/runtime") == "/private/var/lib/runtime"
+
+
+def test_read_all_enforces_bound(tmp_path):
+    path = tmp_path / "large"
+    path.write_bytes(b"0123456789")
+    fd = os.open(path, os.O_RDONLY)
+    try:
+        with pytest.raises(RuntimeError, match="too large"):
+            lease_io.read_all(fd, limit=4)
+        with pytest.raises(RuntimeError, match="too large"):
+            lease_io.read_all(fd, limit=0)
+    finally:
+        os.close(fd)
+
+
+@pytest.mark.parametrize("failure_stage", ["config-parent", "manifest-parent"])
+def test_retry_reasserts_parent_durability_before_success(tmp_path, monkeypatch, failure_stage):
+    events: list[str] = []
+    failed = False
+
+    def fsync(fd: int, stage: str) -> None:
+        nonlocal failed
+        events.append(stage)
+        if stage == failure_stage and not failed:
+            failed = True
+            raise RuntimeError("injected fsync failure")
+
+    monkeypatch.setattr(lease_io, "publication_fsync", fsync)
+    inp = {
+        "data_root": str(tmp_path / "data"), "workspace_id": "abc",
+        "workspace_revision": "a" * 40, "config_hex": b"config".hex(),
+        "manifest_base": {
+            "workspace_id": "abc", "workspace_revision": "a" * 40,
+            "descriptor_git_blob": "b" * 40, "descriptor_sha256": "c" * 64,
+            "descriptor_dev": "1", "descriptor_ino": "2",
+            "config_dwh_binding": {"workspace_id": "abc", "config_fingerprint": "e", "input_fingerprint": "f"},
+        },
+    }
+    with pytest.raises(RuntimeError, match="injected"):
+        lease_io.publish(inp)
+    events.clear()
+    lease_io.publish(inp)
+    assert events.index("config-parent") < events.index("manifest-parent")
diff --git a/harness/tht/config.py b/harness/tht/config.py
index 0124b067..b5c50d62 100644
--- a/harness/tht/config.py
+++ b/harness/tht/config.py
@@ -638,10 +638,11 @@ def _strict_runtime_manifest(raw: object) -> dict[str, object]:
 
 def _canonical_runtime_path(path: Path) -> Path:
     value = str(path)
-    if value == "/tmp" or value.startswith("/tmp/"):
-        return Path("/private" + value)
-    if value == "/var" or value.startswith("/var/"):
-        return Path("/private" + value)
+    if sys.platform == "darwin":
+        if value == "/tmp" or value.startswith("/tmp/"):
+            return Path("/private" + value)
+        if value == "/var" or value.startswith("/var/"):
+            return Path("/private" + value)
     return path
 
 
diff --git a/harness/tht/runtime_config_lease_io.py b/harness/tht/runtime_config_lease_io.py
index 9fc9a2b5..f7885008 100644
--- a/harness/tht/runtime_config_lease_io.py
+++ b/harness/tht/runtime_config_lease_io.py
@@ -12,6 +12,7 @@ import stat
 import subprocess
 import sys
 import tempfile
+import time
 from pathlib import Path
 
 
@@ -20,12 +21,13 @@ def fail(msg: str) -> None:
 
 
 def _canonical_root(root: str) -> str:
-    # Darwin exposes /tmp and /var as symlink aliases.  The trusted path boundary
-    # records the real OS-owned prefix so a manifest never contains a symlink.
-    if root == "/tmp" or root.startswith("/tmp/"):
-        return "/private" + root
-    if root == "/var" or root.startswith("/var/"):
-        return "/private" + root
+    # Darwin exposes /tmp and /var as symlink aliases. Linux does not: rewriting
+    # these paths there would redirect valid installations to a different root.
+    if sys.platform == "darwin":
+        if root == "/tmp" or root.startswith("/tmp/"):
+            return "/private" + root
+        if root == "/var" or root.startswith("/var/"):
+            return "/private" + root
     return root
 
 
@@ -180,7 +182,7 @@ def walk(root: str, comps: list[str], create: bool = True) -> int:
     # macOS exposes temporary directories through the conventional /var and
     # /tmp symlinks. Resolve only these OS-owned aliases; workspace-owned
     # ancestors remain component checked and are never realpath-followed.
-    if root == "/var" or root == "/tmp" or root.startswith(("/var/", "/tmp/")):
+    if sys.platform == "darwin" and (root == "/var" or root == "/tmp" or root.startswith(("/var/", "/tmp/"))):
         root = "/private" + root
     parts = [part for part in Path(root).parts if part not in ("", "/")]
     if any(part in (".", "..") or "/" in part for part in parts + comps):
@@ -249,7 +251,13 @@ def publication_fsync(fd: int, stage: str) -> None:
 
 
 def read_all(fd: int, limit: int = 16 * 1024 * 1024) -> bytes:
+    if limit < 0:
+        fail("runtime config file is too large")
     os.lseek(fd, 0, os.SEEK_SET)
+    if limit == 0:
+        if os.read(fd, 1):
+            fail("runtime config file is too large")
+        return b""
     chunks: list[bytes] = []
     total = 0
     while True:
@@ -258,8 +266,12 @@ def read_all(fd: int, limit: int = 16 * 1024 * 1024) -> bytes:
             return b"".join(chunks)
         chunks.append(chunk)
         total += len(chunk)
-        if total > limit:
-            fail("runtime config file is too large")
+        if total >= limit:
+            # The bounded read above cannot observe an additional byte when it
+            # lands exactly on the ceiling; probe once before accepting it.
+            if os.read(fd, 1):
+                fail("runtime config file is too large")
+            return b"".join(chunks)
 
 
 def strict_manifest(value: object) -> dict:
@@ -341,7 +353,17 @@ def publish(inp: dict) -> dict:
     ])
     # The retained preprocessing directory is the single cross-process lock seam.
     # No pathname lock file is created in the workspace layout.
-    fcntl.flock(prep, fcntl.LOCK_EX)
+    deadline = time.monotonic() + 2.0
+    while True:
+        try:
+            fcntl.flock(prep, fcntl.LOCK_EX | fcntl.LOCK_NB)
+            break
+        except BlockingIOError:
+            if time.monotonic() >= deadline:
+                # Never let a wedged publisher block its caller indefinitely. The
+                # Node boundary turns this stable conflict into a bounded failure.
+                fail("runtime config publication is busy")
+            time.sleep(0.01)
     try:
         name = f"{rev}.yaml"
         mname = f"{rev}.json"
@@ -397,6 +419,10 @@ def publish(inp: dict) -> dict:
             finally:
                 os.close(fd)
             publication_fsync(cfgdir, "config-parent")
+        # A prior invocation may have reported success after publishing the
+        # entry but before its parent fsync. Re-establish that durability
+        # boundary before making the manifest durable.
+        publication_fsync(cfgdir, "config-parent")
         # Identity is deliberately recorded after final no-replace publication.
         got = current(cfgdir, name, 0o400)
         assert got
@@ -462,9 +488,12 @@ def publish(inp: dict) -> dict:
                 except FileNotFoundError:
                     pass
             publication_fsync(mandir, "manifest-parent")
+        # As with the config directory, retries must repair a boundary that
+        # failed after the no-replace publication on an earlier invocation.
+        publication_fsync(mandir, "manifest-parent")
         return {
-            "path": f"{root}/sessions/{wid}/preprocessing/runtime-config/{name}",
-            "manifestPath": f"{root}/sessions/{wid}/preprocessing/runtime-config-manifests/{mname}",
+            "path": f"{canonical}/sessions/{wid}/preprocessing/runtime-config/{name}",
+            "manifestPath": f"{canonical}/sessions/{wid}/preprocessing/runtime-config-manifests/{mname}",
             "manifest": mb.decode(),
             "manifest_sha256": hashlib.sha256(mb).hexdigest(),
             "dev": s.st_dev,
@@ -570,6 +599,20 @@ def verified_snapshot(inp: dict) -> dict:
     git_env.update({"GIT_NO_REPLACE_OBJECTS": "1", "GIT_CONFIG_NOSYSTEM": "1",
                     "GIT_CONFIG_GLOBAL": os.devnull, "GIT_CONFIG_SYSTEM": os.devnull})
     try:
+        # A 40-hex object name is not necessarily a commit (trees and blobs are
+        # valid Git objects and also accept the <object>:path syntax). Require
+        # the raw object itself to be a commit, with replacement/config controls
+        # disabled, before reading any descriptor bytes.
+        object_type = subprocess.check_output(
+            ["git", "--no-replace-objects", "-C", repo, "cat-file", "-t", rev],
+            stderr=subprocess.DEVNULL, text=True, timeout=5, env=git_env,
+        ).strip()
+        resolved_commit = subprocess.check_output(
+            ["git", "--no-replace-objects", "-C", repo, "rev-parse", f"{rev}^{{commit}}"],
+            stderr=subprocess.DEVNULL, text=True, timeout=5, env=git_env,
+        ).strip()
+        if object_type != "commit" or resolved_commit != rev:
+            fail("workspace Git revision is not an exact commit")
         blob = subprocess.check_output(
             ["git", "--no-replace-objects", "-C", repo, "rev-parse", f"{rev}:workspaces/{wid}.yaml"],
             stderr=subprocess.DEVNULL, text=True, timeout=5, env=git_env,
@@ -600,6 +643,11 @@ def verified_snapshot(inp: dict) -> dict:
 
 
 def binding(inp: dict) -> dict:
+    # Runtime handoff variables are capabilities, never helper input. Remove
+    # inherited values before load_config can inspect its environment.
+    for key in tuple(os.environ):
+        if key.startswith(("THT_RUNTIME_CONFIG_", "THT_CONFIG_")):
+            os.environ.pop(key, None)
     try:
         raw = bytes.fromhex(inp["config_hex"])
     except (TypeError, ValueError):
@@ -626,15 +674,22 @@ def binding(inp: dict) -> dict:
 def main() -> None:
     try:
         inp = json.load(sys.stdin)
+        if not isinstance(inp, dict) or inp.get("protocol_version") != 1:
+            fail("unsupported runtime config protocol")
         action = inp.get("action")
+        request_keys = {
+            "publish": {"protocol_version", "action", "data_root", "workspace_id", "workspace_revision", "config_hex", "manifest_base"},
+            "verified-snapshot": {"protocol_version", "action", "snapshots_root", "repository_root", "workspace_revision", "workspace_id"},
+            "binding": {"protocol_version", "action", "config_hex"},
+        }
+        if action not in request_keys or set(inp) != request_keys[action]:
+            fail("invalid runtime config request")
         if action == "publish":
             result = publish(inp)
         elif action == "verified-snapshot":
             result = verified_snapshot(inp)
-        elif action == "binding":
-            result = binding(inp)
         else:
-            fail("unsupported runtime config action")
+            result = binding(inp)
         print(json.dumps(result))
     except Exception as e:  # noqa: BLE001
         print(json.dumps({"error": str(e)}))