feat(ui): add instructions file path field to adapter config forms

Add agent instructions file field to Claude and Codex adapter
config panels, allowing users to specify an absolute path to an
AGENTS.md-style file injected into the system prompt at runtime.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

ui/src/adapters/codex-local/config-fields.tsx

@@ -1,9 +1,16 @@
 import type { AdapterConfigFieldsProps } from "../types";
 import {
+  Field,
   ToggleField,
+  DraftInput,
   help,
 } from "../../components/agent-config-primitives";
 
+const inputClass =
+  "w-full rounded-md border border-border px-2.5 py-1.5 bg-transparent outline-none text-sm font-mono placeholder:text-muted-foreground/40";
+const instructionsFileHint =
+  "Absolute path to a markdown file (e.g. AGENTS.md) that defines this agent's behavior. Injected into the system prompt at runtime.";
+
 export function CodexLocalConfigFields({
   isCreate,
   values,
@@ -17,6 +24,27 @@ export function CodexLocalConfigFields({
 
   return (
     <>
+      <Field label="Agent instructions file" hint={instructionsFileHint}>
+        <DraftInput
+          value={
+            isCreate
+              ? values!.instructionsFilePath ?? ""
+              : eff(
+                  "adapterConfig",
+                  "instructionsFilePath",
+                  String(config.instructionsFilePath ?? ""),
+                )
+          }
+          onCommit={(v) =>
+            isCreate
+              ? set!({ instructionsFilePath: v })
+              : mark("adapterConfig", "instructionsFilePath", v || undefined)
+          }
+          immediate
+          className={inputClass}
+          placeholder="/absolute/path/to/AGENTS.md"
+        />
+      </Field>
       <ToggleField
         label="Bypass sandbox"
         hint={help.dangerouslyBypassSandbox}