Expose job working dir via environment variable

* Expose the job's working dir via `DSTACK_WORKING_DIR` environment variable
* Automatically `cd` to `DSTACK_WORKING_DIR` on login

Closes: #3045

Author: un-def

runner/internal/executor/executor.go

@@ -394,6 +394,7 @@ func (ex *RunExecutor) execJob(ctx context.Context, jobLogFile io.Writer) error
 		"DSTACK_RUN_NAME":       ex.run.RunSpec.RunName,
 		"DSTACK_REPO_ID":        ex.run.RunSpec.RepoId,
 		"DSTACK_REPO_DIR":       ex.repoDir,
+		"DSTACK_WORKING_DIR":    ex.jobWorkingDir,
 		"DSTACK_NODES_IPS":      strings.Join(ex.clusterInfo.JobIPs, "\n"),
 		"DSTACK_MASTER_NODE_IP": ex.clusterInfo.MasterJobIP,
 		"DSTACK_NODE_RANK":      strconv.Itoa(node_rank),
@@ -864,6 +865,9 @@ func writeDstackProfile(env map[string]string, pth string) error {
 			return err
 		}
 	}
+	if _, err = file.WriteString("cd \"$DSTACK_WORKING_DIR\"\n"); err != nil {
+		return err
+	}
 	if err = os.Chmod(pth, 0o644); err != nil {
 		return err
 	}

src/dstack/_internal/server/services/jobs/configurators/base.py

@@ -218,7 +218,15 @@ def _dstack_image_commands(self) -> List[str]:
         ):
             return []
         return [
-            f"uv venv -q --prompt $DSTACK_RUN_NAME --seed -p {self._python()} {DSTACK_DIR}/venv",
+            # `uv` may emit:
+            # > warning: `VIRTUAL_ENV=/dstack/venv` does not match the project environment path
+            # > `.venv` and will be ignored; use `--active` to target the active environment
+            # > instead
+            # Safe to ignore, reusing dstack's venv for `uv` is discouraged (it should only be
+            # used for legacy `pip`-based configurations). `--no-active` suppresses the warning.
+            # Alternatively, the user can call `deactivate` once before using `uv`.
+            # If the user really wants to reuse dstack's venv, they must spefify `--active`.
+            f"uv venv -q --prompt dstack -p {self._python()} --seed {DSTACK_DIR}/venv",
             f"echo '. {DSTACK_DIR}/venv/bin/activate' >> {DSTACK_PROFILE_PATH}",
             f". {DSTACK_DIR}/venv/bin/activate",
         ]