diff --git a/ui/src/adapters/claude-local/config-fields.tsx b/ui/src/adapters/claude-local/config-fields.tsx
index b57024b6..5dd4f5ab 100644
--- a/ui/src/adapters/claude-local/config-fields.tsx
+++ b/ui/src/adapters/claude-local/config-fields.tsx
@@ -6,6 +6,7 @@ import {
   DraftNumberInput,
   help,
 } from "../../components/agent-config-primitives";
+import { ChoosePathButton } from "../../components/PathInstructionsModal";
 
 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";
@@ -23,25 +24,28 @@ export function ClaudeLocalConfigFields({
 }: AdapterConfigFieldsProps) {
   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"
-      />
+      <div className="flex items-center gap-2">
+        <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"
+        />
+        <ChoosePathButton />
+      </div>
     </Field>
   );
 }
diff --git a/ui/src/adapters/codex-local/config-fields.tsx b/ui/src/adapters/codex-local/config-fields.tsx
index e487a7bc..86baff6c 100644
--- a/ui/src/adapters/codex-local/config-fields.tsx
+++ b/ui/src/adapters/codex-local/config-fields.tsx
@@ -5,6 +5,7 @@ import {
   DraftInput,
   help,
 } from "../../components/agent-config-primitives";
+import { ChoosePathButton } from "../../components/PathInstructionsModal";
 
 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";
@@ -25,25 +26,28 @@ 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"
-        />
+        <div className="flex items-center gap-2">
+          <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"
+          />
+          <ChoosePathButton />
+        </div>
       </Field>
       <ToggleField
         label="Bypass sandbox"
diff --git a/ui/src/components/AgentConfigForm.tsx b/ui/src/components/AgentConfigForm.tsx
index 5467ac97..5073f4af 100644
--- a/ui/src/components/AgentConfigForm.tsx
+++ b/ui/src/components/AgentConfigForm.tsx
@@ -35,6 +35,7 @@ import { defaultCreateValues } from "./agent-config-defaults";
 import { getUIAdapter } from "../adapters";
 import { ClaudeLocalAdvancedFields } from "../adapters/claude-local/config-fields";
 import { MarkdownEditor } from "./MarkdownEditor";
+import { ChoosePathButton } from "./PathInstructionsModal";
 
 /* ---- Create mode values ---- */
 
@@ -130,12 +131,6 @@ const claudeThinkingEffortOptions = [
 ] as const;
 
 
-function extractPickedDirectoryPath(handle: unknown): string | null {
-  if (typeof handle !== "object" || handle === null) return null;
-  const maybePath = (handle as { path?: unknown }).path;
-  return typeof maybePath === "string" && maybePath.length > 0 ? maybePath : null;
-}
-
 /* ---- Form ---- */
 
 export function AgentConfigForm(props: AgentConfigFormProps) {
@@ -277,8 +272,6 @@ export function AgentConfigForm(props: AgentConfigFormProps) {
 
   // Section toggle state — advanced always starts collapsed
   const [runPolicyAdvancedOpen, setRunPolicyAdvancedOpen] = useState(false);
-  const [cwdPickerNotice, setCwdPickerNotice] = useState<string | null>(null);
-
   // Popover states
   const [modelOpen, setModelOpen] = useState(false);
   const [thinkingEffortOpen, setThinkingEffortOpen] = useState(false);
@@ -487,40 +480,8 @@ export function AgentConfigForm(props: AgentConfigFormProps) {
                   className="w-full bg-transparent outline-none text-sm font-mono placeholder:text-muted-foreground/40"
                   placeholder="/path/to/project"
                 />
-                <button
-                  type="button"
-                  className="inline-flex items-center rounded-md border border-border px-2 py-0.5 text-xs text-muted-foreground hover:bg-accent/50 transition-colors shrink-0"
-                  onClick={async () => {
-                    try {
-                      setCwdPickerNotice(null);
-                      // @ts-expect-error -- showDirectoryPicker is not in all TS lib defs yet
-                      const handle = await window.showDirectoryPicker({ mode: "read" });
-                      const absolutePath = extractPickedDirectoryPath(handle);
-                      if (absolutePath) {
-                        if (isCreate) set!({ cwd: absolutePath });
-                        else mark("adapterConfig", "cwd", absolutePath);
-                        return;
-                      }
-                      const selectedName =
-                        typeof handle === "object" &&
-                        handle !== null &&
-                        typeof (handle as { name?: unknown }).name === "string"
-                          ? String((handle as { name: string }).name)
-                          : "selected folder";
-                      setCwdPickerNotice(
-                        `Directory picker only exposed "${selectedName}". Paste the absolute path manually.`,
-                      );
-                    } catch {
-                      // user cancelled or API unsupported
-                    }
-                  }}
-                >
-                  Choose
-                </button>
+                <ChoosePathButton />
               </div>
-              {cwdPickerNotice && (
-                <p className="mt-1 text-xs text-amber-400">{cwdPickerNotice}</p>
-              )}
             </Field>
           )}
 
diff --git a/ui/src/components/PathInstructionsModal.tsx b/ui/src/components/PathInstructionsModal.tsx
new file mode 100644
index 00000000..b910dead
--- /dev/null
+++ b/ui/src/components/PathInstructionsModal.tsx
@@ -0,0 +1,143 @@
+import { useState } from "react";
+import { Apple, Monitor, Terminal } from "lucide-react";
+import {
+  Dialog,
+  DialogContent,
+  DialogHeader,
+  DialogTitle,
+  DialogDescription,
+} from "@/components/ui/dialog";
+import { cn } from "@/lib/utils";
+
+type Platform = "mac" | "windows" | "linux";
+
+const platforms: { id: Platform; label: string; icon: typeof Apple }[] = [
+  { id: "mac", label: "macOS", icon: Apple },
+  { id: "windows", label: "Windows", icon: Monitor },
+  { id: "linux", label: "Linux", icon: Terminal },
+];
+
+const instructions: Record<Platform, { steps: string[]; tip?: string }> = {
+  mac: {
+    steps: [
+      "Open Finder and navigate to the folder.",
+      "Right-click (or Control-click) the folder.",
+      "Hold the Option (⌥) key — \"Copy\" changes to \"Copy as Pathname\".",
+      "Click \"Copy as Pathname\", then paste here.",
+    ],
+    tip: "You can also open Terminal, type cd, drag the folder into the terminal window, and press Enter. Then type pwd to see the full path.",
+  },
+  windows: {
+    steps: [
+      "Open File Explorer and navigate to the folder.",
+      "Click in the address bar at the top — the full path will appear.",
+      "Copy the path, then paste here.",
+    ],
+    tip: "Alternatively, hold Shift and right-click the folder, then select \"Copy as path\".",
+  },
+  linux: {
+    steps: [
+      "Open a terminal and navigate to the directory with cd.",
+      "Run pwd to print the full path.",
+      "Copy the output and paste here.",
+    ],
+    tip: "In most file managers, Ctrl+L reveals the full path in the address bar.",
+  },
+};
+
+function detectPlatform(): Platform {
+  const ua = navigator.userAgent.toLowerCase();
+  if (ua.includes("mac")) return "mac";
+  if (ua.includes("win")) return "windows";
+  return "linux";
+}
+
+interface PathInstructionsModalProps {
+  open: boolean;
+  onOpenChange: (open: boolean) => void;
+}
+
+export function PathInstructionsModal({
+  open,
+  onOpenChange,
+}: PathInstructionsModalProps) {
+  const [platform, setPlatform] = useState<Platform>(detectPlatform);
+
+  const current = instructions[platform];
+
+  return (
+    <Dialog open={open} onOpenChange={onOpenChange}>
+      <DialogContent className="sm:max-w-md">
+        <DialogHeader>
+          <DialogTitle className="text-base">How to get a full path</DialogTitle>
+          <DialogDescription>
+            Paste the absolute path (e.g.{" "}
+            <code className="text-xs bg-muted px-1 py-0.5 rounded">/Users/you/project</code>
+            ) into the input field.
+          </DialogDescription>
+        </DialogHeader>
+
+        {/* Platform tabs */}
+        <div className="flex gap-1 rounded-md border border-border p-0.5">
+          {platforms.map((p) => (
+            <button
+              key={p.id}
+              type="button"
+              className={cn(
+                "flex flex-1 items-center justify-center gap-1.5 rounded px-2 py-1 text-xs transition-colors",
+                platform === p.id
+                  ? "bg-accent text-foreground"
+                  : "text-muted-foreground hover:text-foreground hover:bg-accent/50",
+              )}
+              onClick={() => setPlatform(p.id)}
+            >
+              <p.icon className="h-3.5 w-3.5" />
+              {p.label}
+            </button>
+          ))}
+        </div>
+
+        {/* Steps */}
+        <ol className="space-y-2 text-sm">
+          {current.steps.map((step, i) => (
+            <li key={i} className="flex gap-2">
+              <span className="text-muted-foreground font-mono text-xs mt-0.5 shrink-0">
+                {i + 1}.
+              </span>
+              <span>{step}</span>
+            </li>
+          ))}
+        </ol>
+
+        {current.tip && (
+          <p className="text-xs text-muted-foreground border-l-2 border-border pl-3">
+            {current.tip}
+          </p>
+        )}
+      </DialogContent>
+    </Dialog>
+  );
+}
+
+/**
+ * Small "Choose" button that opens the PathInstructionsModal.
+ * Drop-in replacement for the old showDirectoryPicker buttons.
+ */
+export function ChoosePathButton({ className }: { className?: string }) {
+  const [open, setOpen] = useState(false);
+  return (
+    <>
+      <button
+        type="button"
+        className={cn(
+          "inline-flex items-center rounded-md border border-border px-2 py-0.5 text-xs text-muted-foreground hover:bg-accent/50 transition-colors shrink-0",
+          className,
+        )}
+        onClick={() => setOpen(true)}
+      >
+        Choose
+      </button>
+      <PathInstructionsModal open={open} onOpenChange={setOpen} />
+    </>
+  );
+}