diff --git a/src/process/RegexMatcher.ts b/src/process/RegexMatcher.ts
index ff46be6f9d..9e98e4baeb 100644
--- a/src/process/RegexMatcher.ts
+++ b/src/process/RegexMatcher.ts
@@ -555,9 +555,19 @@ export const matchRegexValues = async (input: {
           return finish(
             err(
               input.invalidPattern?.(reply.data.reason) ??
-                new AnalysisInputError(input.operation, {
-                  userMessage: `Invalid regex pattern: ${reply.data.reason}`,
-                }),
+                new AnalysisInputError(
+                  input.operation,
+                  {
+                    userMessage: `Invalid regex pattern: ${reply.data.reason}`,
+                  },
+                  [
+                    {
+                      path: ["pattern"],
+                      reason: "invalid_format",
+                      message: "Supply a valid regular expression.",
+                    },
+                  ],
+                ),
             ),
           );
         if (
diff --git a/tests/boundary/process/regexMatcher.test.ts b/tests/boundary/process/regexMatcher.test.ts
index b5e735e19c..7ffe8dcdf7 100644
--- a/tests/boundary/process/regexMatcher.test.ts
+++ b/tests/boundary/process/regexMatcher.test.ts
@@ -502,6 +502,35 @@ it("preserves Unicode matching order and refuses a pre-cancelled match", async (
   ).toMatchObject({ ok: false, error: { _tag: "AnalysisCancelledError" } });
 });
 
+it("names the rejected pattern field for a default invalid-pattern refusal", async () => {
+  const matched = await matchRegexValues({
+    operation: "search_procedures",
+    pattern: "[",
+    caseSensitive: false,
+    values: ["value"],
+  });
+  expect(matched.ok).toBe(false);
+  if (matched.ok) return;
+  expect(projectAnalysisError(matched.error)).toMatchObject({
+    code: "invalid_request",
+    category: "invalid_input",
+    recovery: {
+      kind: "inspect_input_contract",
+      operation: "search_procedures",
+    },
+    details: {
+      operation: "search_procedures",
+      issues: [
+        {
+          path: ["pattern"],
+          reason: "invalid_format",
+          message: "Supply a valid regular expression.",
+        },
+      ],
+    },
+  });
+});
+
 it("keeps Hopper's result projection and invalid-pattern contract with the shared worker", async () => {
   const search = new HopperRegexSearch({
     callTool: async () =>
diff --git a/tests/boundary/providers/kuna/kunaStrings.test.ts b/tests/boundary/providers/kuna/kunaStrings.test.ts
index 4d1348e954..6454fc27df 100644
--- a/tests/boundary/providers/kuna/kunaStrings.test.ts
+++ b/tests/boundary/providers/kuna/kunaStrings.test.ts
@@ -94,7 +94,13 @@ it("shares a typed string scan across concurrent searches and exact address read
       });
     expect(
       await client.execute("search_strings", { pattern: "[", mode: "regex" }),
-    ).toMatchObject({ ok: false, error: { _tag: "AnalysisInputError" } });
+    ).toMatchObject({
+      ok: false,
+      error: {
+        _tag: "AnalysisInputError",
+        issues: [{ path: ["pattern"], reason: "invalid_format" }],
+      },
+    });
     expect((await run(client, "list_strings")).result).toHaveLength(2);
   } finally {
     expect(await client.close()).toEqual({ ok: true, value: null });