@@ -496,7 +496,26 @@ SEARCH_PREV="$(cat "$SEARCH_MARK" 2>/dev/null || true)"
 SEARCH_PREV="$(printf '%s' "$SEARCH_PREV" | tr -d '[:space:]')"
 if [ -z "$SEARCH_PREV" ] && [ -f "$DATA/.tron-search-kagi" ]; then SEARCH_PREV="kagi"; fi
 
-if command -v python3 >/dev/null 2>&1 && [ "$SEARCH_PREV" != "$SEARCH_WANT" ]; then
+# 3.17.0 marked the move to pit.world done even where it left the engine alone,
+# so profiles on one of Chromium's stock engines (Ecosia, Google, Bing ...) never
+# moved. One more pass replaces a stock engine nobody edited; .tron-search-stock
+# records that it ran.
+SEARCH_STOCK_MARK="$DATA/.tron-search-stock"
+SEARCH_STOCK=0
+if [ "$SEARCH_WANT" = pit ] && [ "$SEARCH_EXPLICIT" = 0 ] && [ ! -f "$SEARCH_STOCK_MARK" ]; then SEARCH_STOCK=1; fi
+
+# Chromium rewrites Preferences from memory when it exits, so an edit made while
+# this profile is open is silently lost. Leave it, and the marks, for a launch
+# that finds the browser closed.
+profile_in_use() {
+  local lock pid
+  lock="$(readlink "$DATA/SingletonLock" 2>/dev/null)" || return 1
+  pid="${lock##*-}"
+  case "$pid" in ''|*[!0-9]*) return 1 ;; esac
+  kill -0 "$pid" 2>/dev/null
+}
+
+if command -v python3 >/dev/null 2>&1 && { [ "$SEARCH_PREV" != "$SEARCH_WANT" ] || [ "$SEARCH_STOCK" = 1 ]; } && ! profile_in_use; then
   SEARCH_PREV_URL=""
   if [ -n "$SEARCH_PREV" ]; then
     SEARCH_PREV_URL="$(search_engine_spec "$SEARCH_PREV" 2>/dev/null | cut -d'|' -f3 || true)"
@@ -505,12 +524,14 @@ if command -v python3 >/dev/null 2>&1 && [ "$SEARCH_PREV" != "$SEARCH_WANT" ]; t
   TB_ENGINE="$(search_engine_spec "$SEARCH_WANT")" \
   TB_PREV_URL="$SEARCH_PREV_URL" \
   TB_FORCE="$SEARCH_EXPLICIT" \
-  python3 - <<'PY' || true
+  TB_STOCK="$SEARCH_STOCK" \
+  python3 - <<'PY' && SEARCH_APPLIED=1 || SEARCH_APPLIED=0
 import json, os, sys, tempfile
 p = os.environ["TB_PREFS"]
 name, keyword, url = os.environ["TB_ENGINE"].split("|")
 prev_url = os.environ.get("TB_PREV_URL", "")
 force = os.environ.get("TB_FORCE") == "1"
+stock = os.environ.get("TB_STOCK") == "1"
 os.makedirs(os.path.dirname(p), exist_ok=True)
 # An existing file that does not parse is LEFT ALONE. Replacing it with a fresh
 # dict is how a profile gets wiped: this file holds every setting in the profile,
@@ -522,7 +543,7 @@ if os.path.exists(p):
             d = json.load(f)
     except Exception:
         sys.stderr.write("TronBrowser: %s did not parse — leaving it untouched.\n" % p)
-        raise SystemExit(0)
+        raise SystemExit(1)
 else:
     d = {}
 
@@ -532,24 +553,38 @@ else:
 # `tron search` is the one case that outranks whatever is currently set.
 cur = d.get("default_search_provider_data", {}).get("template_url_data") or {}
 cur_url = cur.get("url", "")
-if force or not cur_url or (prev_url and cur_url == prev_url):
-    d.setdefault("default_search_provider_data", {})["template_url_data"] = {
+# Chromium's own stock engines (prepopulate_id > 0 and never edited, so still
+# safe_for_autoreplace) are not a choice anyone made in this browser, so the
+# move to pit.world replaces those too.
+is_stock = int(cur.get("prepopulate_id") or 0) > 0 and cur.get("safe_for_autoreplace") is True
+if force or not cur_url or (prev_url and cur_url == prev_url) or (stock and is_stock):
+    engine = {
         "short_name": name,
         "keyword": keyword,
         "url": url,
         "favicon_url": "https://" + keyword.split("/")[0] + "/favicon.ico",
         "safe_for_autoreplace": False,
     }
+    dsp = d.setdefault("default_search_provider_data", {})
+    dsp["template_url_data"] = engine
+    # The mirror and the guid still point at the old engine, and Chromium would
+    # pick it back out of Web Data by that guid.
+    if "mirrored_template_url_data" in dsp:
+        dsp["mirrored_template_url_data"] = dict(engine)
+    (d.get("default_search_provider") or {}).pop("guid", None)
     # Preferences is the profile. A truncated write loses every setting in it,
     # so land it as a rename rather than in place.
     fd, tmp = tempfile.mkstemp(dir=os.path.dirname(p))
     with os.fdopen(fd, "w") as f:
         json.dump(d, f)
     os.replace(tmp, p)
 PY
-  mkdir -p "$DATA"
-  printf '%s\n' "$SEARCH_WANT" > "$SEARCH_MARK" 2>/dev/null || true
-  rm -f "$DATA/.tron-search-kagi" 2>/dev/null || true
+  if [ "$SEARCH_APPLIED" = 1 ]; then
+    mkdir -p "$DATA"
+    printf '%s\n' "$SEARCH_WANT" > "$SEARCH_MARK" 2>/dev/null || true
+    rm -f "$DATA/.tron-search-kagi" 2>/dev/null || true
+    if [ "$SEARCH_WANT" = pit ]; then : > "$SEARCH_STOCK_MARK" 2>/dev/null || true; fi
+  fi
 fi
 
 # Show the feed (ai-sidebar New Tab page) on startup. We can't pass a startup URL —
 
@@ -4,8 +4,8 @@
 // change to flag handling has to survive something before it ships.
 
 import { spawnSync } from 'node:child_process';
-import { mkdtempSync, mkdirSync, copyFileSync, writeFileSync, readFileSync, chmodSync, existsSync, symlinkSync } from 'node:fs';
-import { tmpdir } from 'node:os';
+import { mkdtempSync, mkdirSync, copyFileSync, writeFileSync, readFileSync, chmodSync, existsSync, symlinkSync, unlinkSync } from 'node:fs';
+import { hostname, tmpdir } from 'node:os';
 import { dirname, join } from 'node:path';
 import { fileURLToPath } from 'node:url';
 import { afterEach, describe, expect, it } from 'vitest';
@@ -231,6 +231,72 @@ describe('omnibox search engine', () => {
     expect(dse(first.home).url).toBe(chosen);
   });
 
+  /** A profile whose default is one of Chromium's stock engines, as the choice screen leaves it. */
+  function seedStock(opts: { marker?: string; edited?: boolean } = {}): string {
+    const home = seed({ marker: opts.marker });
+    const ecosia = {
+      short_name: 'Ecosia',
+      keyword: 'ecosia.org',
+      url: 'https://www.ecosia.org/search?q={searchTerms}',
+      prepopulate_id: 101,
+      safe_for_autoreplace: !opts.edited,
+      synced_guid: '485bf7d3-0215-45af-87dc-538868000101',
+    };
+    writeFileSync(
+      prefsPath(home),
+      JSON.stringify({
+        default_search_provider: { guid: ecosia.synced_guid, reset_occurred: false },
+        default_search_provider_data: { template_url_data: ecosia, mirrored_template_url_data: ecosia },
+        bookmark_bar: { show_on_all_tabs: true },
+      }),
+    );
+    return home;
+  }
+
+  it('moves a profile 3.17.0 marked as done but left on a stock engine (Ecosia)', () => {
+    // 3.17.0 wrote .tron-search=pit without touching a stock engine, so the
+    // switch never happened and never retried.
+    const home = seedStock({ marker: 'pit' });
+    run([], { home });
+    const json = JSON.parse(readFileSync(prefsPath(home), 'utf8'));
+    expect(dse(home).url).toBe('https://pit.world/search?q={searchTerms}');
+    expect(json.default_search_provider_data.mirrored_template_url_data.url).toBe('https://pit.world/search?q={searchTerms}');
+    // Chromium would otherwise pull Ecosia back out of Web Data by this guid.
+    expect(json.default_search_provider.guid).toBeUndefined();
+    expect(json.bookmark_bar?.show_on_all_tabs).toBe(true);
+    expect(existsSync(join(home, 'profile', '.tron-search-stock'))).toBe(true);
+  });
+
+  it('keeps a stock engine the user edited', () => {
+    const home = seedStock({ marker: 'pit', edited: true });
+    run([], { home });
+    expect(dse(home).url).toBe('https://www.ecosia.org/search?q={searchTerms}');
+  });
+
+  it('does the stock pass once, so a later choice of a stock engine sticks', () => {
+    const home = seedStock({ marker: 'pit' });
+    run([], { home });
+    const p = prefsPath(home);
+    const json = JSON.parse(readFileSync(p, 'utf8'));
+    json.default_search_provider_data.template_url_data = { url: 'https://www.bing.com/search?q={searchTerms}', prepopulate_id: 3, safe_for_autoreplace: true };
+    writeFileSync(p, JSON.stringify(json));
+    run([], { home });
+    expect(dse(home).url).toBe('https://www.bing.com/search?q={searchTerms}');
+  });
+
+  it('leaves an open profile alone and applies on the next launch', () => {
+    // Chromium rewrites Preferences when it exits, so an edit made under it is lost.
+    const home = seedStock({ marker: 'pit' });
+    const lock = join(home, 'profile', 'SingletonLock');
+    symlinkSync(`${hostname()}-${process.pid}`, lock);
+    run([], { home });
+    expect(dse(home).url).toBe('https://www.ecosia.org/search?q={searchTerms}');
+    expect(existsSync(join(home, 'profile', '.tron-search-stock'))).toBe(false);
+    unlinkSync(lock);
+    run([], { home });
+    expect(dse(home).url).toBe('https://pit.world/search?q={searchTerms}');
+  });
+
   it('keeps the rest of Preferences when it rewrites the engine', () => {
     const home = seed({ url: KAGI_URL, legacyKagi: true });
     run([], { home });