fix(exec): re-run install-tool when switching back to an earlier tool version (#46823)

`install-tool` installs a version and also makes it the active one. The
memo skipped `install-tool` for any tool version already installed in the
run, so after A -> B -> A the last command ran on B. Track the active
version per tool instead and skip only when the requested version is
already active.

Co-authored-by: Claude Opus 5.5 <michael.kriese+claude-code@mend.io>

lib/util/exec/containerbase.spec.ts

@@ -337,6 +337,27 @@ describe('util/exec/containerbase', () => {
           generateInstallCommands(toolConstraints, true),
         ).resolves.toEqual(['install-tool composer 2.2.0']);
       });
+
+      it('re-issues the install command when switching back to an earlier version', async () => {
+        const toolConstraints: ToolConstraint[] = [{ toolName: 'composer' }];
+        await expect(
+          generateInstallCommands(toolConstraints, true),
+        ).resolves.toEqual(['install-tool composer 2.1.0']);
+
+        datasource.getPkgReleases.mockResolvedValueOnce({
+          releases: [{ version: '2.2.0' }],
+        });
+        await expect(
+          generateInstallCommands(toolConstraints, true),
+        ).resolves.toEqual(['install-tool composer 2.2.0']);
+
+        datasource.getPkgReleases.mockResolvedValueOnce({
+          releases: [{ version: '2.1.0' }],
+        });
+        await expect(
+          generateInstallCommands(toolConstraints, true),
+        ).resolves.toEqual(['install-tool composer 2.1.0']);
+      });
     });
   });
 });

lib/util/exec/containerbase.ts

@@ -382,7 +382,9 @@ export async function resolveConstraint(
 
 // Docker execs run in a fresh `--rm` container each time, so `memoize` must
 // stay false there - only the persistent-host (binarySource=install) path
-// can safely skip a tool it has already installed this run.
+// can safely skip a tool whose requested version is already active.
+// `install-tool` also activates the version it installs, so the memo tracks
+// the active version per tool, not every installed version.
 export async function generateInstallCommands(
   toolConstraints: Opt<ToolConstraint[]>,
   memoize = false,
@@ -393,11 +395,11 @@ export async function generateInstallCommands(
       const toolVersion = await resolveConstraint(toolConstraint);
       const { toolName } = toolConstraint;
       if (memoize) {
-        const cacheKey = `containerbase-installed:${toolName}:${toolVersion}`;
-        if (memCache.get<boolean | undefined>(cacheKey)) {
+        const cacheKey = `containerbase-active:${toolName}`;
+        if (memCache.get<string | undefined>(cacheKey) === toolVersion) {
           continue;
         }
-        memCache.set(cacheKey, true);
+        memCache.set(cacheKey, toolVersion);
       }
       const installCommand = `install-tool ${toolName} ${quote(toolVersion)}`;
       installCommands.push(installCommand);