switch conversion_id to use KSUIDs

proto/officeconvertapi/v1/conversion.proto

@@ -62,6 +62,7 @@ message Slide {
 
 // SlideDeck is the final structured conversion artifact.
 message SlideDeck {
+  // Session identifier: KSUID in standard base62 text form. Well-formed values are at most 27 characters (see https://github.com/segmentio/ksuid).
   string conversion_id = 1;
   string source_filename = 2;
   repeated Slide slides = 3;
@@ -78,6 +79,7 @@ message CreateConversionRequest {
 
 // CreateConversionResponse returns upload details for the session.
 message CreateConversionResponse {
+  // Session identifier: KSUID in standard base62 text form. Well-formed values are at most 27 characters (see https://github.com/segmentio/ksuid).
   string conversion_id = 1;
   string upload_bucket = 2;
   string upload_object_key = 3;
@@ -87,22 +89,26 @@ message CreateConversionResponse {
 
 // StartConversionRequest requests conversion of an already uploaded PPTX.
 message StartConversionRequest {
+  // Session identifier: KSUID in standard base62 text form. Well-formed values are at most 27 characters (see https://github.com/segmentio/ksuid).
   string conversion_id = 1;
 }
 
 // StartConversionResponse returns the first known status after enqueue.
 message StartConversionResponse {
+  // Session identifier: KSUID in standard base62 text form. Well-formed values are at most 27 characters (see https://github.com/segmentio/ksuid).
   string conversion_id = 1;
   ConversionStatus status = 2;
 }
 
 // GetConversionStatusRequest asks for a specific conversion status.
 message GetConversionStatusRequest {
+  // Session identifier: KSUID in standard base62 text form. Well-formed values are at most 27 characters (see https://github.com/segmentio/ksuid).
   string conversion_id = 1;
 }
 
 // GetConversionStatusResponse returns current status and optional error info.
 message GetConversionStatusResponse {
+  // Session identifier: KSUID in standard base62 text form. Well-formed values are at most 27 characters (see https://github.com/segmentio/ksuid).
   string conversion_id = 1;
   ConversionStatus status = 2;
   string error_message = 3;
@@ -114,6 +120,7 @@ message GetConversionStatusResponse {
 
 // GetSlideDeckRequest fetches a completed deck.
 message GetSlideDeckRequest {
+  // Session identifier: KSUID in standard base62 text form. Well-formed values are at most 27 characters (see https://github.com/segmentio/ksuid).
   string conversion_id = 1;
 }
 
@@ -124,11 +131,13 @@ message GetSlideDeckResponse {
 
 // DeleteConversionRequest requests immediate cleanup.
 message DeleteConversionRequest {
+  // Session identifier: KSUID in standard base62 text form. Well-formed values are at most 27 characters (see https://github.com/segmentio/ksuid).
   string conversion_id = 1;
 }
 
 // DeleteConversionResponse confirms cleanup details.
 message DeleteConversionResponse {
+  // Session identifier: KSUID in standard base62 text form. Well-formed values are at most 27 characters (see https://github.com/segmentio/ksuid).
   string conversion_id = 1;
   bool deleted = 2;
 }