diff --git a/console/src/fleetToml.ts b/console/src/fleetToml.ts
index 824da9c..dc4a348 100644
--- a/console/src/fleetToml.ts
+++ b/console/src/fleetToml.ts
@@ -7,7 +7,10 @@
 // regex-based (not a full TOML parser) so it's unit-testable and only ever
 // touches the one array/block it means to.
 
-function quote(s: string): string {
+// Exported so fleetsK8sToml.ts (fleets-k8s.toml's client-side edits, same
+// `[fleet.<name>]` shape) can reuse it instead of duplicating a one-line
+// helper.
+export function quote(s: string): string {
   return JSON.stringify(s);
 }
 
diff --git a/console/src/fleetsK8sToml.test.ts b/console/src/fleetsK8sToml.test.ts
new file mode 100644
index 0000000..8b42b82
--- /dev/null
+++ b/console/src/fleetsK8sToml.test.ts
@@ -0,0 +1,57 @@
+import { describe, it, expect } from "vitest";
+import { appendMember, appendK8sFleetBlock } from "./fleetsK8sToml";
+
+describe("appendMember (reused from fleetToml.ts)", () => {
+  it("works against fleets-k8s.toml's [fleet.<name>] shape too", () => {
+    const text = `[fleet.orbstack-dev]
+context = "orbstack"
+namespace = "dev"
+members = ["scratch-agent"]
+`;
+    const out = appendMember(text, "orbstack-dev", "scratch-agent-2");
+    expect(out).toContain('members = ["scratch-agent", "scratch-agent-2"]');
+    expect(out).toContain('context = "orbstack"');
+    expect(out).toContain('namespace = "dev"');
+  });
+});
+
+describe("appendK8sFleetBlock", () => {
+  it("appends a new [fleet.<name>] block with context, namespace, members, expected_principal", () => {
+    const out = appendK8sFleetBlock('default_cluster = "oab"\n', {
+      name: "orbstack-dev",
+      member: "oab-dev-scratch-agent",
+      context: "orbstack",
+      namespace: "dev",
+      expectedPrincipal: "system:serviceaccount:dev:oab-agent",
+    });
+    expect(out).toContain("[fleet.orbstack-dev]");
+    expect(out).toContain('context = "orbstack"');
+    expect(out).toContain('namespace = "dev"');
+    expect(out).toContain('members = ["oab-dev-scratch-agent"]');
+    expect(out).toContain('expected_principal = "system:serviceaccount:dev:oab-agent"');
+  });
+
+  it("omits context and expected_principal when not provided, but always writes namespace", () => {
+    const out = appendK8sFleetBlock("", {
+      name: "orca-k8s",
+      member: "oab-prod-orca",
+      context: null,
+      namespace: "prod",
+      expectedPrincipal: null,
+    });
+    expect(out).not.toContain("context =");
+    expect(out).not.toContain("expected_principal =");
+    expect(out).toContain('namespace = "prod"');
+  });
+
+  it("separates the new block from existing content with exactly one blank line", () => {
+    const out = appendK8sFleetBlock('default_cluster = "oab"\n', {
+      name: "x",
+      member: "m",
+      context: null,
+      namespace: "ns",
+      expectedPrincipal: null,
+    });
+    expect(out).toBe('default_cluster = "oab"\n\n[fleet.x]\nnamespace = "ns"\nmembers = ["m"]\n');
+  });
+});
diff --git a/console/src/fleetsK8sToml.ts b/console/src/fleetsK8sToml.ts
new file mode 100644
index 0000000..37552b2
--- /dev/null
+++ b/console/src/fleetsK8sToml.ts
@@ -0,0 +1,39 @@
+// Pure text-level edits to fleets-k8s.toml's `[fleet.<name>]` blocks — the
+// k8s counterpart to fleetToml.ts, same rationale (studio#104: k8s_fleet_
+// config_write has no partial/append primitive, so the client computes the
+// new/edited TOML and calls it with the full updated text).
+//
+// `[fleet.<name>]` block lookup/append-member is identical between fleets.
+// toml and fleets-k8s.toml (same table shape, same `members = [...]` array —
+// neither `findFleetBlock` nor `appendMember` reference any AWS-specific
+// field), so this module reuses fleetToml.ts's `appendMember` rather than
+// duplicating it. Only "create a brand-new fleet block" differs, since the
+// two files' required/optional fields differ (context+namespace vs
+// region+profile).
+
+import { quote, appendMember } from "./fleetToml";
+
+export { appendMember };
+
+export interface NewK8sFleetEntry {
+  name: string;
+  member: string;
+  context: string | null;
+  namespace: string;
+  expectedPrincipal: string | null;
+}
+
+// Append a brand-new `[fleet.<name>]` block to the end of the file, with the
+// one member — the first instance just deployed. `context` and
+// `expected_principal` are optional fields, omitted rather than written as
+// empty strings (mirrors fleetToml.ts's appendFleetBlock).
+export function appendK8sFleetBlock(text: string, entry: NewK8sFleetEntry): string {
+  const lines = [`[fleet.${entry.name}]`];
+  if (entry.context) lines.push(`context = ${quote(entry.context)}`);
+  lines.push(`namespace = ${quote(entry.namespace)}`);
+  lines.push(`members = [${quote(entry.member)}]`);
+  if (entry.expectedPrincipal) lines.push(`expected_principal = ${quote(entry.expectedPrincipal)}`);
+  const block = `${lines.join("\n")}\n`;
+  const trimmed = text.replace(/\s*$/, "");
+  return trimmed.length ? `${trimmed}\n\n${block}` : block;
+}