diff --git a/docs/api/mcp.md b/docs/api/mcp.md
index d2b1ff4a..1592a8d5 100644
--- a/docs/api/mcp.md
+++ b/docs/api/mcp.md
@@ -7677,7 +7677,7 @@ Does NOT throw when:
 
 > **parseCodexTokenUsage**(`stdout`): [`CodexTokenUsage`](#codextokenusage)
 
-Defined in: [mcp/local-harness.ts:1341](https://github.com/tangle-network/agent-runtime/blob/main/src/mcp/local-harness.ts#L1341)
+Defined in: [mcp/local-harness.ts:1348](https://github.com/tangle-network/agent-runtime/blob/main/src/mcp/local-harness.ts#L1348)
 
 Parse and validate the one terminal usage event emitted by `codex exec --json`.
 
diff --git a/src/mcp/local-harness.ts b/src/mcp/local-harness.ts
index e9574ea3..fdcf3d26 100644
--- a/src/mcp/local-harness.ts
+++ b/src/mcp/local-harness.ts
@@ -409,7 +409,14 @@ export async function runLocalHarness(
     : buildHarnessArgs(harness, taskPrompt, options)
   if (options.codexReproducible) assertCodexReproducibleInvocation(requestedCommand, args)
 
-  const baseEnv = options.env ?? process.env
+  // We spawn the harness with `cwd`, but a harness that resolves its working
+  // directory from `$PWD` rather than `getcwd()` (opencode does; the others may)
+  // inherits the parent's stale `PWD` and edits the WRONG directory — its
+  // worktree diff then comes back empty and the delegation fails with a phantom
+  // "empty patch". Pin `PWD` to `cwd` so the harness edits where it was placed.
+  // `baseEnv` feeds both the codex-isolated and the plain spawn paths below, so
+  // pinning it here covers every runLocalHarness consumer.
+  const baseEnv: NodeJS.ProcessEnv = { ...(options.env ?? process.env), PWD: cwd }
   const isolated = options.codexReproducible
     ? await isolateCodexHome({
         baseEnv,