## Background
Per developer of `tus-js-client`, it is normal to occasionally encounter upload errors. The auto-retry mechanism is meant to address this.
While implementing tab-lock to prevent multiple uploads of the same file, 423_locked was used to detect this scenario. But 423_locked could also mean "the server is busy writing the chunk" (per discussion with Randy), so we kind of disabled the auto-retry mechanism accidentally.
Meanwhile, from a prior discussion with Randy, one of the chunk-writing duration took 3 minutes. Our current maximum of "retry after 15s" wouldn't help.
## Change
1. Given that tab-locking was improved recently and no longer reliant on the server error messages (we use secure storage to mark a file as locked), reverted the change to "skip retry on 409/423". This is now back to normal recommended behavior.
2. `tus-js-client` currently does not support variable retry delay, otherwise we could prolong the delay if the error was 423. Since we know it could take up to 3 minutes, and that we don't know if it's file-size dependant, just add another 30s retry and put a friendlier message asking the user to retry themselves after waiting a bit.
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