diff --git a/apps/gittensory-miner-extension/options.js b/apps/gittensory-miner-extension/options.js
index 6e2c5062ed..694b006953 100644
--- a/apps/gittensory-miner-extension/options.js
+++ b/apps/gittensory-miner-extension/options.js
@@ -15,10 +15,20 @@ function parseRankedCandidatesJson(text) {
   return parsed;
 }
 
+// #5343 dropped the discoveryIndexUrl UI field and stopped reading/writing it, but chrome.storage.sync.set
+// only merges keys -- it never deletes ones an earlier extension version already synced. Without an active
+// purge, a value synced before #5343 stays in the user's account indefinitely. Called from refreshSettings,
+// which runs on every options-page load and again at the end of every save, so it's cleared promptly
+// regardless of which path a given user hits first.
+async function removeLegacyDiscoveryIndexUrl() {
+  await chrome.storage.sync.remove("discoveryIndexUrl");
+}
+
 if (globalThis.__GITTENSORY_MINER_EXTENSION_TEST__) {
   globalThis.__gittensoryMinerOptionsInternals = {
     parseWatchedRepos,
     parseRankedCandidatesJson,
+    removeLegacyDiscoveryIndexUrl,
   };
 }
 
@@ -53,6 +63,7 @@ form.addEventListener("submit", async (event) => {
 
 async function refreshSettings() {
   const stored = await chrome.storage.sync.get({ watchedRepos: [] });
+  await removeLegacyDiscoveryIndexUrl();
   const local = await chrome.storage.local.get({ rankedCandidates: [] });
   const repos = Array.isArray(stored.watchedRepos) ? stored.watchedRepos : [];
   watchedRepos.value = repos.join("\n");
diff --git a/packages/gittensory-miner/docs/env-reference.md b/packages/gittensory-miner/docs/env-reference.md
index e5e9d47277..f34d768564 100644
--- a/packages/gittensory-miner/docs/env-reference.md
+++ b/packages/gittensory-miner/docs/env-reference.md
@@ -12,6 +12,7 @@ Generated by `npm run miner:env-reference`. Do not edit manually.
 | `GITTENSORY_MINER_EVENT_LEDGER_DB` | `lib/event-ledger.js` | (none) |
 | `GITTENSORY_MINER_GOVERNOR_LEDGER_DB` | `lib/governor-ledger.js` | `""` |
 | `GITTENSORY_MINER_GOVERNOR_STATE_DB` | `lib/governor-state.js` | (none) |
+| `GITTENSORY_MINER_KILL_SWITCH` | `lib/config-precedence.js` | `""` |
 | `GITTENSORY_MINER_NO_UPDATE_CHECK` | `lib/update-check.js` | `""` |
 | `GITTENSORY_MINER_ORB_EXPORT_DB` | `lib/orb-export.js` | `""` |
 | `GITTENSORY_MINER_PLAN_STORE_DB` | `lib/plan-store.js` | `""` |
diff --git a/test/unit/miner-extension-content.test.ts b/test/unit/miner-extension-content.test.ts
index a192aada23..cef291fc30 100644
--- a/test/unit/miner-extension-content.test.ts
+++ b/test/unit/miner-extension-content.test.ts
@@ -148,15 +148,18 @@ describe("miner extension opportunity badge", () => {
     expect(() => internals.parseRankedCandidatesJson('{"not":"array"}')).toThrow();
   });
 
-  it("REGRESSION (dead-field removal): no discoveryIndexUrl config field remains anywhere in the extension", () => {
+  it("REGRESSION (dead-field removal): no discoveryIndexUrl config field remains in the UI or background reads", () => {
     expect(optionsHtml).not.toMatch(/discoveryIndexUrl/);
-    expect(optionsScript).not.toMatch(/discoveryIndexUrl/);
     expect(backgroundScript).not.toMatch(/discoveryIndexUrl/);
   });
 
-  it("saves and restores settings without ever writing or reading discoveryIndexUrl", async () => {
-    const synced: Record<string, unknown> = { watchedRepos: [] };
+  it("purges a discoveryIndexUrl value already synced by an older extension version, on load and on save", async () => {
+    const synced: Record<string, unknown> = {
+      watchedRepos: [],
+      discoveryIndexUrl: "https://legacy.example.test/index.json",
+    };
     const setCalls: Array<Record<string, unknown>> = [];
+    const removeCalls: string[] = [];
     const elements = {
       "#settings": createFormMock(),
       "#status": { textContent: "" },
@@ -174,6 +177,10 @@ describe("miner extension opportunity badge", () => {
               setCalls.push(value);
               Object.assign(synced, value);
             },
+            remove: async (key: string) => {
+              removeCalls.push(key);
+              delete synced[key];
+            },
           },
           local: { get: async () => ({ rankedCandidates: [] }), set: async () => {} },
         },
@@ -184,15 +191,32 @@ describe("miner extension opportunity badge", () => {
     const vmContext = createContext(context);
     new Script(optionsScript).runInContext(vmContext);
 
+    // The load-time refreshSettings() the script triggers on evaluation already removed it.
+    await flushPromises();
+    expect(removeCalls).toEqual(["discoveryIndexUrl"]);
+    expect("discoveryIndexUrl" in synced).toBe(false);
+
+    // Re-seed as if another synced device still has the legacy key, then confirm save also purges it.
+    synced.discoveryIndexUrl = "https://legacy.example.test/index.json";
     elements["#watchedRepos"].value = "JSONbored/gittensory";
     await elements["#settings"].dispatchSubmit();
 
     expect(setCalls).toHaveLength(1);
     expect(setCalls[0]).toEqual({ watchedRepos: ["JSONbored/gittensory"] });
+    expect(removeCalls).toEqual(["discoveryIndexUrl", "discoveryIndexUrl"]);
     expect("discoveryIndexUrl" in synced).toBe(false);
   });
+
+  it("directly exposes removeLegacyDiscoveryIndexUrl for the internal purge, not a UI-facing setting", () => {
+    const internals = loadOptionsInternals();
+    expect(typeof internals.removeLegacyDiscoveryIndexUrl).toBe("function");
+  });
 });
 
+function flushPromises() {
+  return new Promise((resolve) => setTimeout(resolve, 0));
+}
+
 function createFormMock() {
   let submitHandler: ((event: { preventDefault: () => void }) => unknown) | null = null;
   return {
@@ -308,5 +332,6 @@ function loadOptionsInternals() {
   return vmContext.__gittensoryMinerOptionsInternals as {
     parseWatchedRepos: (text: string) => string[];
     parseRankedCandidatesJson: (text: string) => unknown[];
+    removeLegacyDiscoveryIndexUrl: () => Promise<void>;
   };
 }