Merge branch 'ds/maintenance-part-3'

Parts of "git maintenance" to ease writing crontab entries (and
other scheduling system configuration) for it.

* ds/maintenance-part-3:
  maintenance: add troubleshooting guide to docs
  maintenance: use 'incremental' strategy by default
  maintenance: create maintenance.strategy config
  maintenance: add start/stop subcommands
  maintenance: add [un]register subcommands
  for-each-repo: run subcommands on configured repos
  maintenance: add --schedule option and config
  maintenance: optionally skip --auto process

diff --cc .gitignore
Simple merge

diff --cc Makefile
Simple merge

diff --cc builtin.h
Simple merge

diff --cc builtin/gc.c
Simple merge

diff --cc git.c
Simple merge

diff --cc t/helper/test-tool.c
Simple merge

diff --cc t/helper/test-tool.h
Simple merge

diff --cc t/t7900-maintenance.sh
Simple merge

diff --cc t/test-lib.sh
index fa347ed3e1d476291abcb4186705543f52914d70,4a60d1ed76632ecc1d24c5f6b52c3c5962449499..a863ccee7e9a6a24183cdaa8e5bdc07b20fa24ee
--- 1/t/test-lib.sh
--- 2/t/test-lib.sh
+++ b/t/test-lib.sh
@@@ -1711,10 -1702,9 +1711,17 @@@ test_lazy_prereq SHA1 
  test_lazy_prereq REBASE_P '
        test -z "$GIT_TEST_SKIP_REBASE_P"
  '
+ 
 +# Special-purpose prereq for transitioning to a new default branch name:
 +# Some tests need more than just a mindless (case-preserving) s/master/main/g
 +# replacement. The non-trivial adjustments are guarded behind this
 +# prerequisite, acting kind of as a feature flag
 +test_lazy_prereq PREPARE_FOR_MAIN_BRANCH '
 +      test "$GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME" = main
 +'
++
+ # Ensure that no test accidentally triggers a Git command
+ # that runs 'crontab', affecting a user's cron schedule.
+ # Tests that verify the cron integration must set this locally
+ # to avoid errors.
+ GIT_TEST_CRONTAB="exit 1"