filer: drop dead INVALID_PARAMETER_VALUE branch (real conflicts use existing sentinels)

Verified against a real workspace by uploading varied content into pre-existing
paths of mismatched node types: every cross-type collision the server can
produce surfaces as either:

  - 400 RESOURCE_ALREADY_EXISTS, or
  - 409 ALREADY_EXISTS

both already caught by errors.Is(err, ErrResourceAlreadyExists) /
errors.Is(err, ErrAlreadyExists). The "400 INVALID_PARAMETER_VALUE with
'Requested node type [X] is different from the existing node type [Y]'"
shape was hypothesized in the original PR but does not occur in practice
on /workspace/import — the branch was dead code.

Replace the corresponding unit test with one that pins the actual cross-type
collision shape (409 ALREADY_EXISTS with "Node with name X already exists").

Co-authored-by: Isaac

Author: shreyas-goenka

libs/filer/workspace_files_client.go

@@ -11,7 +11,6 @@ import (
 	"net/http"
 	"path"
 	"slices"
-	"strings"
 	"time"
 
 	"github.com/databricks/databricks-sdk-go"
@@ -209,24 +208,15 @@ func (w *WorkspaceFilesClient) Write(ctx context.Context, name string, reader io
 		return w.Write(ctx, name, bytes.NewReader(body), sliceWithout(mode, CreateParentDirectories)...)
 	}
 
-	// File already exists at the path. The /workspace/import endpoint reports this
-	// with two different error_codes depending on whether the conflict was detected
-	// sequentially (400 RESOURCE_ALREADY_EXISTS) or under concurrent contention
-	// (409 ALREADY_EXISTS, observed in TestLock). Both are already-exists from the
-	// caller's perspective.
-	//
-	// Existing-object-with-mismatched-node-type (e.g. uploading a regular .py when a
-	// NOTEBOOK is at the path) surfaces as 400 INVALID_PARAMETER_VALUE with a
-	// "Requested node type" message — also already-exists from the caller's perspective.
+	// Path already taken. /workspace/import returns 400 RESOURCE_ALREADY_EXISTS
+	// for sequential conflicts and 409 ALREADY_EXISTS under concurrent contention
+	// (observed in TestLock). Same-path collisions where the existing object is a
+	// different node type (e.g. NOTEBOOK at /a/foo, upload regular content to
+	// /a/foo) also surface here — verified against a real workspace, the server
+	// returns one of the two already-exists codes regardless of the type mismatch.
 	if errors.Is(err, apierr.ErrResourceAlreadyExists) || errors.Is(err, apierr.ErrAlreadyExists) {
 		return fileAlreadyExistsError{absPath}
 	}
-	if errors.Is(err, apierr.ErrInvalidParameterValue) {
-		var aerr *apierr.APIError
-		if errors.As(err, &aerr) && strings.Contains(aerr.Message, "Requested node type") {
-			return fileAlreadyExistsError{absPath}
-		}
-	}
 
 	// Caller has read access but no write access.
 	if errors.Is(err, apierr.ErrPermissionDenied) {

libs/filer/workspace_files_client_test.go

@@ -187,16 +187,20 @@ func TestWorkspaceFilesClientWriteErrorMapping(t *testing.T) {
 			expectErrTarget: fileAlreadyExistsError{},
 		},
 		{
-			name: "400 INVALID_PARAMETER_VALUE node type mismatch maps to fileAlreadyExistsError",
+			// Verified against a real workspace: when an existing NOTEBOOK at /a/foo
+			// (uploaded earlier as /a/foo.py with the source header) blocks a
+			// regular-content upload to /a/foo, the server returns 409 ALREADY_EXISTS
+			// rather than a node-type-specific code.
+			name: "409 ALREADY_EXISTS for cross-type collision maps to fileAlreadyExistsError",
 			apiErr: &apierr.APIError{
-				StatusCode: http.StatusBadRequest,
-				ErrorCode:  "INVALID_PARAMETER_VALUE",
-				Message:    "Requested node type [FILE] is different from the existing node type [NOTEBOOK]",
+				StatusCode: http.StatusConflict,
+				ErrorCode:  "ALREADY_EXISTS",
+				Message:    "Node with name /dir/foo.py already exists. Please pass overwrite=true to update it.",
 			},
 			expectErrTarget: fileAlreadyExistsError{},
 		},
 		{
-			name: "400 INVALID_PARAMETER_VALUE other message passes through",
+			name: "400 INVALID_PARAMETER_VALUE passes through",
 			apiErr: &apierr.APIError{
 				StatusCode: http.StatusBadRequest,
 				ErrorCode:  "INVALID_PARAMETER_VALUE",