fix(cli): upgrades never overwrite a file at the t3 command's path

apps/desktop/src/app/DesktopCliCommand.test.ts

@@ -178,6 +178,21 @@ it.layer(NodeServices.layer)("DesktopCliCommand", (it) => {
       yield* command.uninstall;
       expect(yield* fs.readFileString(theirs)).toBe("npm's t3\n");
       expect(yield* fs.readLink(path.join(home, "bin", "t3"))).toBe(path.join(home, "gone"));
+      // Another tool's link that leads on to this app's launcher is still that tool's.
+      yield* command.install.pipe(Effect.ignore);
+      const managed = path.join(home, "manager", "t3");
+      yield* fs.makeDirectory(path.dirname(managed));
+      yield* fs.symlink(path.join(home, ".t3", "bin", "t3"), managed);
+      yield* fs.remove(path.join(home, "bin", "t3"));
+      yield* fs.symlink(managed, path.join(home, "bin", "t3"));
+      yield* command.uninstall;
+      expect(yield* fs.readLink(path.join(home, "bin", "t3"))).toBe(managed);
+      // A target that names a folder never runs the launcher, so it is not this app's.
+      const asFolder = `${path.join(home, ".t3", "bin", "t3")}/.`;
+      yield* fs.remove(path.join(home, "bin", "t3"));
+      yield* fs.symlink(asFolder, path.join(home, "bin", "t3"));
+      yield* command.uninstall;
+      expect(yield* fs.readLink(path.join(home, "bin", "t3"))).toBe(asFolder);
 
       const launcher = path.join(home, ".t3", "bin", "t3");
       yield* fs.writeFileString(launcher, "npm's t3\n");
@@ -242,6 +257,41 @@ it.layer(NodeServices.layer)("DesktopCliCommand", (it) => {
     }).pipe(Effect.scoped),
   );
 
+  it.effect("keeps a t3 another program writes while it replaces its own link", () =>
+    Effect.gen(function* () {
+      const fs = yield* FileSystem.FileSystem;
+      const path = yield* Path.Path;
+      const home = yield* fs.makeTempDirectoryScoped();
+      const before = yield* commandIn({ home, baseDir: path.join(home, "old-t3") });
+      const link = (yield* before.install).installedPath!;
+      const theirs = path.join(home, "theirs");
+      yield* fs.writeFileString(theirs, "#!/bin/sh\n", { mode: 0o755 });
+      // Right after the app finds its old link, another program puts its own t3 there.
+      let raced = false;
+      const racing = FileSystem.FileSystem.of({
+        ...fs,
+        access: (target, options) =>
+          (raced
+            ? Effect.void
+            : fs
+                .symlink(theirs, `${link}.new`)
+                .pipe(
+                  Effect.andThen(fs.rename(`${link}.new`, link)),
+                  Effect.andThen(Effect.sync(() => (raced = true))),
+                )
+          ).pipe(Effect.andThen(fs.access(target, options))),
+      });
+      const after = yield* commandIn({ home, baseDir: path.join(home, "new-t3") }).pipe(
+        Effect.provideService(FileSystem.FileSystem, racing),
+      );
+      const installed = yield* after.install;
+      expect(raced).toBe(true);
+      expect(yield* fs.readLink(link)).toBe(theirs);
+      expect(installed.installedPath).toBe(path.join(home, "bin", "t3"));
+      expect(yield* fs.readDirectory(path.dirname(link))).toEqual(["t3"]);
+    }).pipe(Effect.scoped),
+  );
+
   it.effect("refuses to install behind another t3 that runs first", () =>
     Effect.gen(function* () {
       const fs = yield* FileSystem.FileSystem;

apps/desktop/src/app/DesktopCliCommand.ts

@@ -7,13 +7,14 @@ import * as Effect from "effect/Effect";
 import * as FileSystem from "effect/FileSystem";
 import * as Layer from "effect/Layer";
 import * as Option from "effect/Option";
-import * as Random from "effect/Random";
+import * as Path from "effect/Path";
 import * as Schema from "effect/Schema";
 import * as Semaphore from "effect/Semaphore";
 import * as Stream from "effect/Stream";
 import * as ChildProcess from "effect/process/ChildProcess";
 import * as ChildProcessSpawner from "effect/process/ChildProcessSpawner";
 
+import { readLinkText, replaceOwnedLink } from "@t3tools/shared/ownedLink";
 import { pathSetup, readUserLoginShell } from "@t3tools/shared/shell";
 
 import * as DesktopCliShim from "./DesktopCliShim.ts";
@@ -98,16 +99,29 @@ export const make = Effect.gen(function* () {
 
   const isOurLink = Effect.fn("DesktopCliCommand.isOurLink")(
     function* (link: string) {
-      yield* fs.readLink(link);
+      // Only a direct link: a chain through another tool's link is that tool's. Unnormalized,
+      // so a target the OS would refuse (`t3/.`) fails here too.
+      const text = Option.getOrUndefined(yield* readLinkText(link));
+      // Text that is not UTF-8 names another file than the one the OS follows.
+      if (text === undefined) return false;
+      const target = path.isAbsolute(text) ? text : `${path.dirname(link)}${path.sep}${text}`;
+      if (Option.isSome(yield* fs.readLink(target).pipe(Effect.option))) return false;
       // The launcher is a few KB; never read a large binary another `t3` links to.
-      const info = yield* fs.stat(link);
+      const info = yield* fs.stat(target);
       if (info.type !== "File" || Number(info.size) > 16_384) return false;
-      const content = yield* fs.readFileString(link);
+      const content = yield* fs.readFileString(target);
       return content.includes(DesktopCliShim.MARKER);
     },
     Effect.orElseSucceed(() => false),
   );
 
+  /** Other programs write these folders too, so the link is checked again once moved aside. */
+  const replaceOurLink = (input: { readonly link: string; readonly target?: string }) =>
+    replaceOwnedLink({ ...input, owns: isOurLink }).pipe(
+      Effect.provideService(FileSystem.FileSystem, fs),
+      Effect.provideService(Path.Path, path),
+    );
+
   // PATH can reach the regular launcher directly; removal still requires isOurLink.
   const runsOurLauncher = Effect.fn("DesktopCliCommand.runsOurLauncher")(
     // Another T3 home's link is marked too, so compare where it leads, not the marker alone.
@@ -326,26 +340,23 @@ export const make = Effect.gen(function* () {
           );
       if (!created) continue;
       // Our own link is swapped in place; anything else there makes symlink fail and stays.
-      const staging = `${link}.${yield* Random.nextIntBetween(0, 0xffffff)}.tmp`;
       const linked = yield* (
         link === replaced
-          ? fs
-              .symlink(launcher, staging)
-              .pipe(
-                Effect.andThen(
-                  fs
-                    .rename(staging, link)
-                    .pipe(Effect.tapError(() => fs.remove(staging).pipe(Effect.ignore))),
-                ),
-              )
-          : fs.symlink(launcher, link)
+          ? replaceOurLink({ link, target: launcher })
+          : fs.symlink(launcher, link).pipe(Effect.as(true))
       ).pipe(
-        Effect.as(true),
-        Effect.orElseSucceed(() => false),
+        // A moved-aside entry that could not go back is reported, not left for another folder.
+        Effect.catchTags({ OwnedLinkError: (error) => Effect.fail(fail(error.message)) }),
+        Effect.catchTags({ PlatformError: () => Effect.succeed(false) }),
       );
       if (!linked) continue;
       if (replaced !== undefined && replaced !== link) {
-        yield* fs.remove(replaced).pipe(Effect.ignore);
+        yield* replaceOurLink({ link: replaced }).pipe(
+          Effect.catchTags({
+            OwnedLinkError: (error) => Effect.fail(fail(error.message)),
+            PlatformError: () => Effect.void,
+          }),
+        );
       }
       return yield* state;
     }
@@ -367,7 +378,9 @@ export const make = Effect.gen(function* () {
     for (const directory of knownLocations(environment.homeDirectory, environment.platform)) {
       const link = path.join(directory, "t3");
       if (yield* isOurLink(link)) {
-        yield* fs.remove(link).pipe(Effect.mapError(() => fail(`Could not remove ${link}.`)));
+        yield* replaceOurLink({ link }).pipe(
+          Effect.mapError((error) => fail(`Could not remove ${link}: ${error.message}`)),
+        );
       }
     }
     return yield* state;

apps/desktop/src/app/DesktopCliShim.ts

@@ -1,3 +1,4 @@
+import { DESKTOP_CLI_LAUNCHER_MARKER } from "@t3tools/shared/desktopCliLauncher";
 import * as Cause from "effect/Cause";
 import * as Effect from "effect/Effect";
 import * as FileSystem from "effect/FileSystem";
@@ -10,7 +11,7 @@ import { makeComponentLogger } from "./DesktopObservability.ts";
 // AppImage mounts change each run; the launcher must mount the image itself.
 const { logInfo, logWarning } = makeComponentLogger("desktop-cli-shim");
 
-export const MARKER = "Written by T3 Code: runs the desktop app's bundled t3 CLI.";
+export const MARKER = DESKTOP_CLI_LAUNCHER_MARKER;
 
 const SERVER_ENTRY = "apps/server/dist/bin.mjs";