Magic-folder erroneously creates ".conflict" files after joining a folder and restarting

[cypher]

Note: I'm splitting this specific issue off of #2911 since there are two separate bugs described there (which might be resolved/addressed separately):

I have a magic-folder full of Cat Pics on my dev VM which contains the following:

drwxr-xr-x  2 user user 4.0K Jan 15 14:30 .
drwxr-xr-x 77 user user  12K Jan 29 08:57 ..
-rw-------  1 user user 144K Sep 19 22:21 Cheshire Cat.jpeg
-rw-------  1 user user 264K Jan 10 20:24 Colonel Meow.jpg
-rw-------  1 user user 197K Jan 10 20:24 Garfield.jpg
-rw-------  1 user user 271K Jan 10 20:27 Grumpy Cat.jpg
-rw-------  1 user user 1.2M Jan 20 15:42 Kitler.png
-rw-------  1 user user 333K Jan 10 15:14 lolcat.jpg
-rw-------  1 user user 241K Jan 10 15:14 Nala.jpg
-rw-------  1 user user 368K Jan 20 17:13 Venus.jpg
-rw-------  1 user user 1.2M Jan 10 20:24 Waffles.jpg

When I create a magic-folder invite for this folder and join the folder on another testing VM, I see the following on the test VM (after restarting tahoe and allowing the first download/sync):

drwxr-xr-x  2 user user    4096 Jan 29 08:54 .
drwxr-xr-x 14 user user    4096 Jan 29 08:54 ..
-rw-------  1 user user  147098 Sep 19 22:21 Cheshire Cat.jpeg
-rw-------  1 user user  147098 Sep 19 22:21 Cheshire Cat.jpeg.conflict
-rw-------  1 user user  270297 Jan 10 20:24 Colonel Meow.jpg
-rw-------  1 user user  270297 Jan 10 20:24 Colonel Meow.jpg.conflict
-rw-------  1 user user  201576 Jan 10 20:24 Garfield.jpg
-rw-------  1 user user  201576 Jan 10 20:24 Garfield.jpg.conflict
-rw-------  1 user user  277284 Jan 10 20:27 Grumpy Cat.jpg
-rw-------  1 user user  277284 Jan 10 20:27 Grumpy Cat.jpg.conflict
-rw-------  1 user user 1249635 Jan 20 15:42 Kitler.png
-rw-------  1 user user 1249635 Jan 20 15:42 Kitler.png.conflict
-rw-------  1 user user  340635 Jan 10 15:14 lolcat.jpg
-rw-------  1 user user  340635 Jan 10 15:14 lolcat.jpg.conflict
-rw-------  1 user user  245995 Jan 10 15:14 Nala.jpg
-rw-------  1 user user  245995 Jan 10 15:14 Nala.jpg.conflict
-rw-------  1 user user  376601 Jan 20 17:13 Venus.jpg
-rw-------  1 user user  376601 Jan 20 17:13 Venus.jpg.conflict
-rw-------  1 user user 1178092 Jan 10 20:24 Waffles.jpg
-rw-------  1 user user 1178092 Jan 10 20:24 Waffles.jpg.conflict

The conflict files are identical:

user@test:~$ sha256sum Cat\ Pics/*
37586d9e7054e1187fa66debade178aab11c22dd06740807f5a1f86bb64c8b61  Cat Pics/Cheshire Cat.jpeg
37586d9e7054e1187fa66debade178aab11c22dd06740807f5a1f86bb64c8b61  Cat Pics/Cheshire Cat.jpeg.conflict
f01d7e67416905d99327ff3e770a97660aeee1e0819b4857b37c53eb8ffbc1f2  Cat Pics/Colonel Meow.jpg
f01d7e67416905d99327ff3e770a97660aeee1e0819b4857b37c53eb8ffbc1f2  Cat Pics/Colonel Meow.jpg.conflict
7db0c3cfb8feaae5e87f9fb4fc63de09e2d4fefa5d3b4b59a5633c6759c445c6  Cat Pics/Garfield.jpg
7db0c3cfb8feaae5e87f9fb4fc63de09e2d4fefa5d3b4b59a5633c6759c445c6  Cat Pics/Garfield.jpg.conflict
fe9200fb3c2916c13efb05ead60ca71c314c63b396fcb06d37170fe67e5d2a71  Cat Pics/Grumpy Cat.jpg
fe9200fb3c2916c13efb05ead60ca71c314c63b396fcb06d37170fe67e5d2a71  Cat Pics/Grumpy Cat.jpg.conflict
710c8ad0a2dd0a5dcc2cc72b4c804d924a276d54f4ca07d1a9f30f76e8ddbcb6  Cat Pics/Kitler.png
710c8ad0a2dd0a5dcc2cc72b4c804d924a276d54f4ca07d1a9f30f76e8ddbcb6  Cat Pics/Kitler.png.conflict
cb62f377b7c0c6d05daa7663bf508bbf2306042433f299a6e693f572dd22d206  Cat Pics/lolcat.jpg
cb62f377b7c0c6d05daa7663bf508bbf2306042433f299a6e693f572dd22d206  Cat Pics/lolcat.jpg.conflict
bc574478acf95571dd578c278a1567e6fdda546c732d723b38795831795c9d5a  Cat Pics/Nala.jpg
bc574478acf95571dd578c278a1567e6fdda546c732d723b38795831795c9d5a  Cat Pics/Nala.jpg.conflict
86a8eb5643ec3e37385b9993f9012a155425508617238f54c4217d66298e7f15  Cat Pics/Venus.jpg
86a8eb5643ec3e37385b9993f9012a155425508617238f54c4217d66298e7f15  Cat Pics/Venus.jpg.conflict
0f8eec20639c55c47fafc778e88649d801ce91982e5da8a63ee58b2fa81c2f37  Cat Pics/Waffles.jpg
0f8eec20639c55c47fafc778e88649d801ce91982e5da8a63ee58b2fa81c2f37  Cat Pics/Waffles.jpg.conflict

As a user, I would expect there to be no conflict files after I've joined a folder (unless, of course, I did something -- like modified said files before the download(s) completed).

[exarkun]

​https://github.com/tahoe-lafs/tahoe-lafs/pull/575

[GitHub <noreply@…>]

In 528e451/trunk:

Merge pull request #575 from tahoe-lafs/2965.erroneous-conflicts-at-startup

Avoid some start-up time erroneous Magic-Folder conflict files

Fixes: ticket:2965