git-remote-annex: Fix buggy behavior when annex.stalldetection is configured

Make programPath never return "git-remote-annex" or other known multi-call
program names, which are not git-annex and won't behave like it.
If the git-annex binary gets installed under some entirely other name,
it will still return it.

This change exposed that readProgramFile actually could crash,
which happened before only if getExecutablePath was not absolute
and there was no ~/.config/git-annex/program. So fixed that to catch
exception.

Annex/Path.hs

@@ -1,6 +1,6 @@
 {- git-annex program path
  -
- - Copyright 2013-2022 Joey Hess <id@joeyh.name>
+ - Copyright 2013-2024 Joey Hess <id@joeyh.name>
  -
  - Licensed under the GNU AGPL version 3 or higher.
  -}
@@ -18,9 +18,11 @@ import Annex.Common
 import Config.Files
 import Utility.Env
 import Annex.PidLock
+import CmdLine.Multicall
 import qualified Annex
 
 import System.Environment (getExecutablePath, getArgs, getProgName)
+import qualified Data.Map as M
 
 {- A fully qualified path to the currently running git-annex program.
  - 
@@ -33,23 +35,35 @@ import System.Environment (getExecutablePath, getArgs, getProgName)
  - getExecutablePath. It sets GIT_ANNEX_DIR to the location of the
  - standalone build directory, and there are wrapper scripts for git-annex
  - and git-annex-shell in that directory.
+ -
+ - When the currently running program is not git-annex, but is instead eg
+ - git-annex-shell or git-remote-annex, this finds a git-annex program
+ - instead.
  -}
 programPath :: IO FilePath
 programPath = go =<< getEnv "GIT_ANNEX_DIR"
   where
 	go (Just dir) = do
-		name <- getProgName
+		name <- reqgitannex <$> getProgName
 		return (dir </> name)
 	go Nothing = do
-		exe <- getExecutablePath
+		name <- getProgName
+		exe <- if isgitannex name
+			then getExecutablePath
+			else pure "git-annex"
 		p <- if isAbsolute exe
 			then return exe
 			else fromMaybe exe <$> readProgramFile
 		maybe cannotFindProgram return =<< searchPath p
 
+	reqgitannex name
+		| isgitannex name = name
+		| otherwise = "git-annex"
+	isgitannex = flip M.notMember otherMulticallCommands
+
 {- Returns the path for git-annex that is recorded in the programFile. -}
 readProgramFile :: IO (Maybe FilePath)
-readProgramFile = do
+readProgramFile = catchDefaultIO Nothing $ do
 	programfile <- programFile
 	headMaybe . lines <$> readFile programfile