diff --git a/apps/dashboard/src/app/(dashboard)/projects/[id]/[[...slug]]/page.tsx b/apps/dashboard/src/app/(dashboard)/projects/[id]/[[...slug]]/page.tsx
index 0d0bf6630..cfafa0c93 100644
--- a/apps/dashboard/src/app/(dashboard)/projects/[id]/[[...slug]]/page.tsx
+++ b/apps/dashboard/src/app/(dashboard)/projects/[id]/[[...slug]]/page.tsx
@@ -32,7 +32,11 @@ import { DraftProjectView } from "../components/DraftProjectView";
 import { environmentErrorMessage, environmentWizardHref } from "../components/environment-next";
 import { getProjectStatus } from "@/utils/project-status";
 import { useProjectSettings } from "@/context/ProjectSettingsContext";
-import { useProjectInfo, PROJECT_INFO_NOT_FOUND } from "@/hooks/useProjectEndpoints";
+import {
+  invalidateProjectCaches,
+  useProjectInfo,
+  PROJECT_INFO_NOT_FOUND,
+} from "@/hooks/useProjectEndpoints";
 import Link from "next/link";
 import { useRouter, useSearchParams } from "next/navigation";
 import { useToast } from "@/context/ToastContext";
@@ -598,6 +602,22 @@ const ProjectSettingsContent = () => {
     // Optimistic - immediately show "Deleting" status
     setProjectData((prev: any) => ({ ...prev, deletedAt: new Date().toISOString() }));
 
+    // #657: teardown removed THIS environment, but every sibling's cached
+    // /info bundle still lists it — their switchers would keep showing the
+    // dead entry until a hard reload. Drop all known ids on the way out.
+    // Only invoked on success; a failed delete keeps every cache as-is.
+    // Accepted cost: invalidateProjectCaches evicts overview/geo/usage too,
+    // per id — pure eviction for unmounted siblings (only mounted hooks
+    // refetch), so no request storm; just a slower first paint next visit.
+    const invalidateAfterTeardown = () => {
+      const ids = new Set<string>([projectData.id]);
+      for (const env of environments ?? []) {
+        const eid = String(env?.id ?? "");
+        if (eid) ids.add(eid);
+      }
+      ids.forEach((eid) => invalidateProjectCaches(eid));
+    };
+
     try {
       const response = await projectsApi.delete(projectData.id, {
         wipeVolumes,
@@ -651,6 +671,7 @@ const ProjectSettingsContent = () => {
           );
         }
         invalidateSidebarNavCounts();
+        invalidateAfterTeardown();
         router.push("/");
         return;
       }
@@ -667,6 +688,7 @@ const ProjectSettingsContent = () => {
           t.projects.delete.partialCleanupTitle,
         );
         invalidateSidebarNavCounts();
+        invalidateAfterTeardown();
         router.push("/");
         return;
       }
@@ -784,10 +806,14 @@ const ProjectSettingsContent = () => {
         return;
       }
 
-      // 404: someone else already deleted the project in another tab.
+      // 404: someone else already deleted the project in another tab. Not a
+      // failure — the row IS gone — so this is a third success exit, and the
+      // one where this tab's cached bundles are GUARANTEED stale rather than
+      // merely possibly (#657).
       if (err instanceof ApiError && err.status === 404) {
         showToast(t.projects.delete.alreadyDeleted, "success");
         invalidateSidebarNavCounts();
+        invalidateAfterTeardown();
         router.push("/");
         return;
       }
diff --git a/apps/dashboard/src/context/ProjectSettingsContext.tsx b/apps/dashboard/src/context/ProjectSettingsContext.tsx
index 293b3fea8..11b9d215c 100644
--- a/apps/dashboard/src/context/ProjectSettingsContext.tsx
+++ b/apps/dashboard/src/context/ProjectSettingsContext.tsx
@@ -15,7 +15,11 @@ import { useRouter } from "next/navigation";
 import { useI18n } from "@/components/i18n-provider";
 import { usePlatform } from "@/context/PlatformContext";
 import { projectsApi, servicesApi, type Service } from "@/lib/api";
-import { PROJECT_INFO_NOT_FOUND, useProjectInfo } from "@/hooks/useProjectEndpoints";
+import {
+  invalidateProjectCaches,
+  PROJECT_INFO_NOT_FOUND,
+  useProjectInfo,
+} from "@/hooks/useProjectEndpoints";
 import type { ActiveMigration } from "@/utils/project-status";
 import { dedupeServerLogs } from "./server-log-dedup";
 import { beginServicesFetch, failServicesFetch } from "./services-fetch-state";
@@ -809,10 +813,21 @@ export const ProjectSettingsProvider: React.FC<ProviderProps> = ({
       if (!response.success || !response.data) {
         throw new Error(response.error || "Failed to create environment");
       }
+      // #657: the mutation changed the environments list — which is bundled
+      // into EVERY environment's /info payload. Drop those caches NOW or the
+      // next projectInfo emit re-runs the effect above and writes the stale
+      // bundle back over refreshEnvironments' fresh patch, and the new
+      // environment vanishes until a hard reload. Self first, then the known
+      // siblings whose cached bundles are missing the new entry.
+      invalidateProjectCaches(id);
+      for (const env of environments) {
+        const eid = String(env?.id ?? "");
+        if (eid && eid !== String(id)) invalidateProjectCaches(eid);
+      }
       await refreshEnvironments();
       return response.data as ProjectEnvironment;
     },
-    [id, refreshEnvironments],
+    [id, refreshEnvironments, environments],
   );
 
   // Terminal Logs Management
diff --git a/apps/dashboard/src/context/project-settings-environments.test.ts b/apps/dashboard/src/context/project-settings-environments.test.ts
new file mode 100644
index 000000000..f008030b2
--- /dev/null
+++ b/apps/dashboard/src/context/project-settings-environments.test.ts
@@ -0,0 +1,92 @@
+import { describe, expect, it } from "vitest";
+import { readFileSync } from "node:fs";
+import { dirname, join } from "node:path";
+import { fileURLToPath } from "node:url";
+
+/**
+ * Where the environments list is written, and why every environment mutation
+ * must also drop the project caches (#657).
+ *
+ * The `environments` state in ProjectSettingsContext has TWO writers: the
+ * effect that re-seeds it from the bundled /info payload whenever
+ * `projectInfo` changes, and `refreshEnvironments()` which patches it from the
+ * dedicated list endpoint. A create/delete that only patches the second one
+ * loses: the module-level infoCache still holds the OLD bundle, so the next
+ * `projectInfo` emit re-runs the effect and writes the stale list back over
+ * the fresh one — the new environment vanishes (or the deleted one lingers)
+ * until a hard reload.
+ *
+ * The list ships inside EVERY environment's /info payload, so siblings'
+ * cached bundles go stale too — hence invalidating known sibling ids, not
+ * just the current one.
+ *
+ * The fix is wiring, not logic — invisible to a typecheck and to a static
+ * render, and there is no jsdom harness for this provider — so like
+ * advanced-migration-session.test.ts it is pinned here in source.
+ */
+const here = dirname(fileURLToPath(import.meta.url));
+const context = readFileSync(join(here, "./ProjectSettingsContext.tsx"), "utf8");
+const page = readFileSync(
+  join(here, "../app/(dashboard)/projects/[id]/[[...slug]]/page.tsx"),
+  "utf8",
+);
+
+describe("creating an environment survives the next projectInfo emit", () => {
+  // Anchored on the return, not a byte count: everything up to it is the
+  // mutation's success path, and a comment added above cannot slide it.
+  const createEnvironment = context.slice(context.indexOf("const createEnvironment = useCallback"));
+  const body = createEnvironment.slice(0, createEnvironment.indexOf("return response.data"));
+
+  it("drops the stale info cache instead of only patching the derived copy", () => {
+    expect(body).toContain("invalidateProjectCaches(id)");
+    // Sibling bundles carry the shared list too; dropping only the current id
+    // leaves every OTHER cached page missing the new entry until a reload.
+    expect(body).toContain("eid !== String(id)");
+  });
+
+  it("invalidates BEFORE refreshing, so no emit can race the stale bundle back in", () => {
+    // Order is the bug: refreshEnvironments' correct patch only holds until
+    // the cached bundle is re-emitted. Invalidation has to land first.
+    expect(body.indexOf("invalidateProjectCaches(id)")).toBeLessThan(
+      body.indexOf("await refreshEnvironments()"),
+    );
+  });
+});
+
+describe("deleting an environment leaves no dead entry behind", () => {
+  const handler = page.slice(
+    page.indexOf("const handleDeleteProject"),
+    page.indexOf("const renderTabContent"),
+  );
+
+  // Pinned on the helper's DEFINITION: proves the teardown actually drops
+  // caches rather than that a function by that name exists.
+  const helper = handler.slice(
+    handler.indexOf("const invalidateAfterTeardown = "),
+    handler.indexOf("\n    try {"),
+  );
+
+  it("invalidates every known id — the deleted one and its stale siblings", () => {
+    expect(helper).toContain("invalidateProjectCaches(eid)");
+    expect(helper).toContain("for (const env of environments ?? [])");
+  });
+
+  it("runs on ALL THREE success exits", () => {
+    // Two inside try (full ok + unrecoverable-partial) and the 404 in catch:
+    // another tab already deleted the row, so this tab's caches are
+    // guaranteed stale there. Real failures (409 active-work,
+    // deletion-in-progress, teardown-failed) must NOT invalidate.
+    expect(handler.split("invalidateAfterTeardown();").length - 1).toBeGreaterThanOrEqual(3);
+  });
+
+  it("the cross-tab 404 exit invalidates before navigating home", () => {
+    const notFoundExit = handler.slice(
+      handler.indexOf("// 404: someone else already deleted"),
+      handler.indexOf("showToast(getApiErrorMessage(err"),
+    );
+    expect(notFoundExit).toContain("invalidateAfterTeardown();");
+    expect(notFoundExit.indexOf("invalidateAfterTeardown();")).toBeLessThan(
+      notFoundExit.indexOf('router.push("/")'),
+    );
+  });
+});