fix: invalidate stale repository SSH probes

web/workspace/src/lib/workspace/repositories/ssh-connection.ts

@@ -1,5 +1,65 @@
 import type { WorkspaceRuntimeResource } from "$lib/generated/workspace-api";
 
+export type RepositorySshProbeSelection<T> = Readonly<{
+  changed: boolean;
+  runtimeId: string;
+  probe: T | null;
+  selectedHostKey: string;
+}>;
+
+export function changeRepositorySshProbeRuntime<T>(
+  currentRuntimeId: string,
+  nextRuntimeId: string,
+  probe: T | null,
+  selectedHostKey: string,
+): RepositorySshProbeSelection<T> {
+  if (currentRuntimeId === nextRuntimeId) {
+    return {
+      changed: false,
+      runtimeId: currentRuntimeId,
+      probe,
+      selectedHostKey,
+    };
+  }
+  return {
+    changed: true,
+    runtimeId: nextRuntimeId,
+    probe: null,
+    selectedHostKey: "",
+  };
+}
+
+export type RepositorySshProbeOperation = Readonly<{
+  runtimeId: string;
+  generation: number;
+}>;
+
+export class RepositorySshProbeFence {
+  #runtimeId: string | null = null;
+  #generation = 0;
+
+  enter(runtimeId: string): number {
+    if (this.#runtimeId !== runtimeId) {
+      this.#runtimeId = runtimeId;
+      this.#generation += 1;
+    }
+    return this.#generation;
+  }
+
+  capture(runtimeId: string): RepositorySshProbeOperation {
+    return { runtimeId, generation: this.enter(runtimeId) };
+  }
+
+  isCurrent(
+    operation: RepositorySshProbeOperation,
+    runtimeId: string,
+  ): boolean {
+    return operation.runtimeId === runtimeId &&
+      operation.generation === this.#generation &&
+      this.#runtimeId === runtimeId;
+  }
+}
+
 export function repositorySshProbeRuntimes(
   runtimes: readonly WorkspaceRuntimeResource[],
 ): WorkspaceRuntimeResource[] {

web/workspace/src/routes/w/[workspaceId]/repositories/[repositoryKey]/+page.svelte

@@ -7,7 +7,11 @@
   import { parseRepositorySshHostTrust } from '$lib/workspace/api/repository-access';
   import { formatDate, workspaceApiPath } from '$lib/workspace/api/http';
   import { parseRepositorySshConnectionProbeResponse } from '$lib/workspace/api/workspace-model';
-  import { repositorySshProbeRuntimes } from '$lib/workspace/repositories/ssh-connection';
+  import {
+    changeRepositorySshProbeRuntime,
+    RepositorySshProbeFence,
+    repositorySshProbeRuntimes
+  } from '$lib/workspace/repositories/ssh-connection';
   import type { PageProps } from './$types';
 
   let { data }: PageProps = $props();
@@ -16,11 +20,28 @@
   let selectedHostKey = $state('');
   let pending = $state(false);
   let connectionMessage = $state<string | null>(null);
+  const probeFence = new RepositorySshProbeFence();
   const probeRuntimes = $derived(data.runtimes ? repositorySshProbeRuntimes(data.runtimes.items) : []);
 
+  function selectRuntime(runtimeId: string) {
+    const selection = changeRepositorySshProbeRuntime(
+      selectedRuntimeId,
+      runtimeId,
+      probe,
+      selectedHostKey
+    );
+    if (!selection.changed) return;
+    selectedRuntimeId = selection.runtimeId;
+    probe = selection.probe;
+    selectedHostKey = selection.selectedHostKey;
+    probeFence.enter(runtimeId);
+    connectionMessage = null;
+    pending = false;
+  }
+
   $effect(() => {
     if (!selectedRuntimeId) {
-      selectedRuntimeId = probeRuntimes[0]?.runtime_id ?? '';
+      selectRuntime(probeRuntimes[0]?.runtime_id ?? '');
     }
   });
 
@@ -45,42 +66,52 @@
   }
 
   async function runConnectionTest() {
+    const operation = probeFence.capture(selectedRuntimeId);
     pending = true;
     connectionMessage = null;
     probe = null;
     selectedHostKey = '';
     try {
-      const body: RepositorySshConnectionProbeRequest = { runtime_id: selectedRuntimeId };
+      const body: RepositorySshConnectionProbeRequest = { runtime_id: operation.runtimeId };
-      probe = parseRepositorySshConnectionProbeResponse(await requestConnectionTest('POST', body));
+      const nextProbe = parseRepositorySshConnectionProbeResponse(await requestConnectionTest('POST', body));
+      if (!probeFence.isCurrent(operation, selectedRuntimeId)) return;
+      if (nextProbe.runtime_id !== operation.runtimeId) {
+        throw new Error('SSH connection test returned a different Runtime');
+      }
+      probe = nextProbe;
       selectedHostKey = probe.candidates[0]?.host_key ?? '';
       connectionMessage = probe.trust_state === 'verified'
         ? 'The observed SSH host key matches the Workspace trust record.'
         : 'Review the observed fingerprint before trusting this SSH host.';
     } catch (error) {
+      if (!probeFence.isCurrent(operation, selectedRuntimeId)) return;
       connectionMessage = error instanceof Error ? error.message : 'SSH connection test failed';
     } finally {
-      pending = false;
+      if (probeFence.isCurrent(operation, selectedRuntimeId)) pending = false;
     }
   }
 
   async function confirmHostTrust() {
-    if (!probe || !selectedHostKey) return;
+    if (!probe || !selectedHostKey || probe.runtime_id !== selectedRuntimeId) return;
+    const operation = probeFence.capture(selectedRuntimeId);
     pending = true;
     connectionMessage = null;
     try {
       const body: ConfirmRepositorySshHostTrustRequest = {
         operation_id: `repository-ssh-confirm-${crypto.randomUUID()}`,
-        runtime_id: probe.runtime_id,
+        runtime_id: operation.runtimeId,
         host_key: selectedHostKey,
         expected_host_trust_revision: probe.expected_host_trust_revision
       };
       parseRepositorySshHostTrust(await requestConnectionTest('PUT', body));
+      if (!probeFence.isCurrent(operation, selectedRuntimeId)) return;
       probe = { ...probe, trust_state: 'verified' };
       connectionMessage = 'SSH host trust saved. Future connections must present this key.';
     } catch (error) {
+      if (!probeFence.isCurrent(operation, selectedRuntimeId)) return;
       connectionMessage = error instanceof Error ? error.message : 'Failed to save SSH host trust';
     } finally {
-      pending = false;
+      if (probeFence.isCurrent(operation, selectedRuntimeId)) pending = false;
     }
   }
 </script>
@@ -167,7 +198,7 @@
     {:else if data.runtimes}
       <label>
         <span>Runtime</span>
-        <select bind:value={selectedRuntimeId} disabled={pending}>
+        <select value={selectedRuntimeId} onchange={(event) => selectRuntime(event.currentTarget.value)}>
           {#each probeRuntimes as runtime}
             <option value={runtime.runtime_id}>{runtime.label} · {runtime.runtime_id}</option>
           {/each}

web/workspace/test/repository-ssh-connection-ui.test.ts

@@ -1,7 +1,11 @@
 import { assert, assertEquals } from "jsr:@std/assert";
 import type { WorkspaceRuntimeResource } from "../src/lib/generated/workspace-api.ts";
 import { parseRepositorySshConnectionProbeResponse } from "../src/lib/workspace/api/workspace-model.ts";
-import { repositorySshProbeRuntimes } from "../src/lib/workspace/repositories/ssh-connection.ts";
+import {
+  changeRepositorySshProbeRuntime,
+  RepositorySshProbeFence,
+  repositorySshProbeRuntimes,
+} from "../src/lib/workspace/repositories/ssh-connection.ts";
 
 const root = new URL("../", import.meta.url);
 const pageSource = await Deno.readTextFile(
@@ -84,6 +88,47 @@ Deno.test("Repository SSH probe offers configured remote Runtimes regardless of
   );
 });
 
+Deno.test("changing the SSH probe Runtime clears the prior result and confirmation key", () => {
+  const runtimeAProbe = {
+    runtime_id: "runtime-a",
+    candidates: [{ host_key: "ssh-ed25519 runtime-a" }],
+  };
+
+  assertEquals(
+    changeRepositorySshProbeRuntime(
+      "runtime-a",
+      "runtime-b",
+      runtimeAProbe,
+      "ssh-ed25519 runtime-a",
+    ),
+    {
+      changed: true,
+      runtimeId: "runtime-b",
+      probe: null,
+      selectedHostKey: "",
+    },
+  );
+});
+
+Deno.test("a delayed SSH probe response cannot apply after the Runtime changes", async () => {
+  const fence = new RepositorySshProbeFence();
+  const operation = fence.capture("runtime-a");
+  let renderedRuntimeId: string | null = null;
+  let resolveProbe!: (runtimeId: string) => void;
+  const delayedProbe = new Promise<string>((resolve) => {
+    resolveProbe = resolve;
+  }).then((runtimeId) => {
+    if (fence.isCurrent(operation, "runtime-b")) {
+      renderedRuntimeId = runtimeId;
+    }
+  });
+
+  fence.enter("runtime-b");
+  resolveProbe("runtime-a");
+  await delayedProbe;
+  assertEquals(renderedRuntimeId, null);
+});
+
 Deno.test("Repository SSH connection test requires an explicit host-key confirmation", () => {
   for (
     const token of [