fix(installer): execute post-install script as single process

Previously each line of the post-install script ran as a separate
/bin/zsh -c process, breaking multi-line constructs (if/then/fi,
for/do/done, variable sharing, heredocs). Now all commands are joined
and executed as a single script.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: fullstackjam

internal/installer/installer.go

@@ -722,20 +722,18 @@ func stepPostInstall(cfg *config.Config) error {
 	}
 
 	var errs []error
-	for _, command := range commands {
-		if cfg.DryRun {
+	if cfg.DryRun {
+		for _, command := range commands {
 			fmt.Printf("[DRY-RUN] Would run: %s\n", command)
-			continue
 		}
-
-		cmd := exec.Command("/bin/zsh", "-c", command)
+	} else {
+		script := strings.Join(commands, "\n")
+		cmd := exec.Command("/bin/zsh", "-c", script)
 		cmd.Stdout = os.Stdout
 		cmd.Stderr = os.Stderr
 		cmd.Dir = home
-
 		if err := cmd.Run(); err != nil {
-			ui.Error(fmt.Sprintf("Command failed: %s", command))
-			errs = append(errs, fmt.Errorf("post-install %q: %w", command, err))
+			errs = append(errs, fmt.Errorf("post-install script: %w", err))
 		}
 	}
 

internal/installer/installer_test.go

@@ -607,7 +607,7 @@ func TestStepPostInstall_CommandFailureReturnsSoftError(t *testing.T) {
 
 	err := stepPostInstall(cfg)
 	assert.Error(t, err)
-	assert.Contains(t, err.Error(), "post-install")
+	assert.Contains(t, err.Error(), "post-install script")
 }
 
 func TestStepPostInstall_ContinuesAfterCommandFailure(t *testing.T) {
@@ -618,17 +618,44 @@ func TestStepPostInstall_ContinuesAfterCommandFailure(t *testing.T) {
 	cfg := &config.Config{
 		Silent: true,
 		RemoteConfig: &config.RemoteConfig{
-			PostInstall: []string{"exit 1", "touch " + markerFile},
+			// Use "false" (a command that fails with exit 1) instead of "exit 1"
+			// because exit terminates the entire script, while false just sets $?.
+			PostInstall: []string{"false", "touch " + markerFile},
 		},
 	}
 
+	// With single-script execution, zsh runs all lines without set -e,
+	// so the second command runs and the script exits 0 (touch succeeds).
 	err := stepPostInstall(cfg)
-	assert.Error(t, err)
+	assert.NoError(t, err)
 
 	_, statErr := os.Stat(markerFile)
 	assert.NoError(t, statErr, "second command should still run after first fails")
 }
 
+func TestStepPostInstall_SharedContext(t *testing.T) {
+	tmpDir := t.TempDir()
+	t.Setenv("HOME", tmpDir)
+
+	markerFile := tmpDir + "/shared-context"
+	cfg := &config.Config{
+		Silent: true,
+		RemoteConfig: &config.RemoteConfig{
+			PostInstall: []string{
+				"MY_VAR=hello",
+				"echo $MY_VAR > " + markerFile,
+			},
+		},
+	}
+
+	err := stepPostInstall(cfg)
+	assert.NoError(t, err)
+
+	content, readErr := os.ReadFile(markerFile)
+	assert.NoError(t, readErr)
+	assert.Equal(t, "hello\n", string(content), "variable set on one line should be available on the next")
+}
+
 func TestRunCustomInstall_WithPostInstallScript(t *testing.T) {
 	tmpDir := t.TempDir()
 	t.Setenv("HOME", tmpDir)