gpg: can't connect to the gpg-agent: IPC connect call failed

[Frank Eskesen]

Hi Cygwin,

I have a problem. I'm running Windows 10 Cygwin and hadn't updated 
Cygwin since July 16. I updated Windows 10 on 8/7 installing KB5064838 
(.NET 8.9.19 Update for x64 Client.) I have two Windows 11 machines, and 
a virtual Windows 10 machine last updated 7/15.

None of the other machines have this problem. All machines copy the 
~/.gnupg file. They also each have a copy of an encrypted password file. 
One of the Windows 11 machines is new. I've been building it and am now 
configuring it.

The new Windows 11 machine had a problem I was able to fix. I caused 
this problem by using gpg before copying the .gnupg directory, so the 
directory was created with a common.conf file containing "use-keyboxd". 
When copying the .gnupg directory I kept existing files, so that 
configuration directive caused gpg  to ignore secret keys. Removing that 
file fixed the problem on that machine.

Then I went back to the Windows 10 machine updated with KB5064838. Now, 
with no significant changes other than KB5064838, gpg fails as follows:
(This runs inside a script)
```
+ gpg -vv --output home --decrypt home.gpg
gpg: enabled compatibility flags:
# off=0 ctb=85 tag=1 hlen=3 plen=268
:pubkey enc packet: version 3, algo 1, keyid 05916FDA5225F00E
         data: [2047 bits]
gpg: public key is 05916FDA5225F00E
# off=271 ctb=d4 tag=20 hlen=2 plen=0 partial new-ctb
:aead encrypted packet: cipher=9 aead=2 cb=16
         length: unknown
gpg: using subkey 05916FDA5225F00E instead of primary key 0D4A2C912C5594AD
gpg: encrypted with rsa2048 key, ID 05916FDA5225F00E, created 2025-04-11
       "***** ******* <*********@gmail.com>"
gpg: using pgp trust model
gpg: key 568B3948A0D16ADB: accepted as trusted key
gpg: key 0D4A2C912C5594AD: accepted as trusted key
gpg: no running gpg-agent - starting '/usr/bin/gpg-agent'
gpg: waiting for the agent to come up ... (8s)
gpg: waiting for the agent to come up ... (7s)
gpg: waiting for the agent to come up ... (6s)
gpg: waiting for the agent to come up ... (5s)
gpg: waiting for the agent to come up ... (4s)
gpg: waiting for the agent to come up ... (3s)
gpg: waiting for the agent to come up ... (2s)
gpg: waiting for the agent to come up ... (1s)
gpg: can't connect to the gpg-agent: IPC connect call failed
gpg: no running gpg-agent - starting '/usr/bin/gpg-agent'
gpg: waiting for the agent to come up ... (8s)
: (Repeated)
gpg: keydb_search failed: No agent running
gpg: public key decryption failed: No secret key
gpg: decryption failed: No secret key
+ rc=2
+ [[ 2 != 0 ]]
+ rm home
+ echo 'ERROR: Decryption failure 2.'
ERROR: Decryption failure 2.
+ echo 'No file changed.'
No file changed.
+ exit 1
```
The agent actually starts and gpg-agent.exe shows up in process list 
(three times.) After the script ends gpg-agent.exe (apparently times out 
and) terminates.

I have since fully updated Cygwin and Windows 10 (applying today's 
update) but the problem still recurs. I'm not going to update the 
virtual Windows 10 machine.

I tried uninstall the update, but the recovery environment didn't think 
I had Administrator privileges (probably because I only log in with a 
local account) and system restore could only get me back as far as 
August 9th.

My working theory is that KB5064838 causes this problem. I don't know 
enough about IPC or Cygwin internals to have confidence in the theory, 
though.

Thanks,
F. Eskesen