hooks: ship three commented examples, install them, document the contract

Add hooks/on_start, hooks/on_done and hooks/on_quit. They are named
after the hooks themselves so copying one into ~/.config/ttym/hooks/ is
the entire installation step, and each carries its argument contract in
a header comment.

  on_start  sets the terminal window title to what is running
  on_done   desktop notification plus a sound, both backgrounded, with
            the first available of paplay/aplay/mpv/ffplay
  on_quit   records abandoned sessions to a TSV under XDG_STATE_HOME and
            restores the terminal title

make install places them in PREFIX/share/doc/ttym/hooks; make uninstall
removes them and both directories; make dist ships hooks/ with the
executable bits intact.

The man page's HOOKS section now documents what the code actually does
rather than what could be assumed from the call sites:

  - $2 differs per hook: requested duration on on_start, full duration
    on on_done, and time actually elapsed -- excluding time spent paused
    -- on on_quit. An abandoned 25m countdown reports what really ran.
  - $3 is always passed, so it is never unset.
  - hooks block: timer forks and waitpid()s, so on_done delays the
    completion bell and the alert loop. Background anything slow.
  - stdin, stdout and stderr all go to /dev/null, which is why printing
    is pointless and cannot corrupt the redrawn progress line.
  - execvp(3) means a script needs a #! line.

README gains a Hooks section. All three examples pass sh -n and
shellcheck, and were tested end to end through the documented flow:
make install to a staging prefix, copy into a config dir, run.

Claude-Session: https://claude.ai/code/session_01APLBs8RB1FcUaC4viVkzbP

1 files changed, 78 insertions, 11 deletions

diff --git a/timer.1 b/timer.1
index e72566f..e3fe0bc 100644
--- a/timer.1
+++ b/timer.1
@@ -254,17 +254,79 @@ or
 .BR Ctrl+C ,
 or when a stopwatch is stopped.
 .PP
-Each hook is executed synchronously with three arguments:
-.IR mode ,
-.IR duration_seconds ,
-.IR comment .
-The first is
-.BR countdown
-or
-.BR stopwatch ;
-the others come from the running session. Hooks must be marked
-executable. Standard streams are redirected to
-.IR /dev/null .
+A hook is any executable file at that name; there is nothing to enable.
+A file that is missing or not marked executable is skipped silently.
+.SS Arguments
+Each hook is run with exactly three positional arguments.
+.TP
+.B $1
+.BR countdown " or " stopwatch .
+.TP
+.B $2
+Seconds. The meaning depends on the hook:
+.RS
+.IP \(bu 2
+.BR on_start :
+the requested duration of a countdown, or
+.B 0
+for a stopwatch.
+.IP \(bu 2
+.BR on_done :
+the full duration that elapsed.
+.IP \(bu 2
+.BR on_quit :
+the time actually elapsed, excluding any time spent paused. A countdown
+abandoned after two seconds reports
+.BR 2 ,
+not the duration that was asked for.
+.RE
+.TP
+.B $3
+The
+.B \-c
+text, or an empty string. Always passed, so
+.B $3
+is never unset.
+.SS Execution
+Hooks run synchronously:
+.B timer
+forks, executes the hook and waits for it. A slow hook delays the timer
+\(em
+.B on_start
+delays the first frame, and
+.B on_done
+delays the completion bell and the alert loop. Background anything slow
+with
+.BR & .
+.PP
+Standard input, output and error are all redirected to
+.IR /dev/null ,
+so a hook cannot print to the terminal and cannot corrupt the redrawn
+progress line. Write to a file, to
+.BR logger (1),
+or to a notification daemon instead. The exit status is discarded: a
+failing hook cannot abort the timer.
+.PP
+Hooks are executed with
+.BR execvp (3),
+so a script needs a
+.B #!
+line like any other.
+.SS Examples
+Three commented, working examples ship with the source and are installed
+to
+.IR PREFIX/share/doc/ttym/hooks/ .
+They set the terminal title, send a desktop notification and play a
+sound on completion, and record abandoned sessions to a TSV file. Copy
+the ones you want and edit:
+.PP
+.RS
+.nf
+mkdir \-p ~/.config/ttym/hooks
+cp /usr/local/share/doc/ttym/hooks/on_done ~/.config/ttym/hooks/
+chmod +x ~/.config/ttym/hooks/on_done
+.fi
+.RE
 .SH EXIT STATUS
 .TP
 .B 0
@@ -340,6 +402,11 @@ Directory containing the
 .B on_quit
 executables described in
 .BR HOOKS .
+.TP
+.I PREFIX/share/doc/ttym/hooks/
+Commented example hooks, installed by
+.BR "make install" .
+Copy them into the directory above to use them.
 .SH EXAMPLES
 A twenty\-five minute work session, tagged for later stats:
 .PP