Rust core: YAML grid config, navigation state machine, evdev input

Replaces the three shell scripts' logic with one binary. tmux stays the
pane engine; src/session/ is the only module that knows that.

The grid model: coordinates are sparse ordinals, so only their sort order
matters and a socktop group is one cell however many hosts it holds.
Horizontal movement walks a cell's sub-sequence (tiled overview, then each
host zoomed) and leaves only after the last one; entry direction decides
whether you land on the first or last sub-screen. Vertical movement returns
to where you were in that row, and snaps to the nearest column only on the
first visit.

Notable details found while building:

* Unquoted "at: 0x0" is hexadecimal 0 to YAML, and "1x0" is not valid hex,
  so only the row-0 entries would break. Deserialization catches the integer
  case and names the fix.
* Panes are addressed by tmux id, never index, and each command is wrapped
  so the pane outlives it. v1's remain-on-exit cannot do this: it is a
  per-window option that new windows do not inherit, so a monitor that exits
  during construction destroys its window and the next split fails with
  "no current target". Now a dead monitor stays on screen with its status.
* Contact-count averaging, not summing: a panel reporting one finger as
  three contacts must not look like three times the travel.
* Movement subcommands wait for the move to happen and report where they
  landed, so they are scriptable rather than fire-and-forget.

36 tests: the grid model, the gesture classifier and an end-to-end pass
against a real tmux server.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

config.example.yaml

@@ -0,0 +1,128 @@
+# socktop-swipe configuration.
+#
+# Copy to ~/.config/socktop-swipe/config.yaml and edit. After every change run
+#
+#     socktop-swipe validate
+#
+# which resolves the grid, prints the map and checks that every program it would
+# run actually exists.
+
+# ---------------------------------------------------------------------------
+# Session
+# ---------------------------------------------------------------------------
+
+# tmux session name. Change only if it collides with something else.
+session: socktop-swipe
+
+# Terminal that `socktop-swipe run` opens the dashboard in. It is invoked as
+#     <terminal> -e tmux attach -t <session>
+# Remove this line to attach in the current terminal instead.
+terminal: alacritty
+
+# Show a position indicator in the tmux status line: what is above, where you
+# are, what is below. Useful once the grid has more than one row.
+indicator: false
+
+# Full paths to the monitor programs. i3 and non-login shells do not have
+# ~/.cargo/bin on PATH, so setting them here saves repeating a path on every
+# screen. A bare name is looked up on PATH. Leading ~/ is expanded.
+binaries:
+  socktop: ~/.cargo/bin/socktop
+  uptime-kuma-status: ~/.cargo/bin/uptime-kuma-status
+  unifly: ~/Documents/GitHub/unifly/target/release-small/unifly
+
+# ---------------------------------------------------------------------------
+# Touch panel
+# ---------------------------------------------------------------------------
+
+touch:
+  # ALWAYS a /dev/input/by-id/ path -- eventN numbers get reshuffled on reboot
+  # or USB re-enumeration. `socktop-swipe doctor --list` shows the candidates.
+  device: /dev/input/by-id/usb-ILITEK_ILITEK-TOUCH-event-if00
+
+  # The PANEL's resolution, not the X screen. With a second monitor attached X
+  # reports the combined root window (e.g. 2304x720), which is not this.
+  width: 1280
+  height: 720
+
+  # Take the panel exclusively, so X never sees the touches. Without this, one
+  # swipe reaches several consumers at once: the terminal reads 2-contact swipes
+  # as pinch-zoom and socktop turns on its own all-motion mouse reporting. Set
+  # false only if you also want touch to work in other applications, and then
+  # install the X ignore rule instead -- see the README.
+  grab: true
+
+  # Pixels of travel before a drag counts as a swipe. Measured on the ILITEK
+  # panel: real swipes land at 150-260px, accidental contact under 70px.
+  threshold: 80
+
+  # Degrees off-axis tolerated, maximum 45. Real finger swipes came in 1-25
+  # degrees off true horizontal, so 30 leaves comfortable margin.
+  leniency: 30
+
+  # Contact counts accepted for one logical swipe.
+  #
+  # THE SETTING MOST LIKELY TO NEED CHANGING ON NEW HARDWARE. Many multipoint
+  # panels report 2 or even 3 contacts for a physically one-finger swipe. If
+  # swipes are detected but nothing happens, `socktop-swipe doctor` will say so
+  # in as many words.
+  fingers: [1, 2, 3]
+
+# Swipe directions, named by finger motion. RL is right-to-left.
+gestures:
+  forward: RL     # move deeper into the grid
+  back: LR
+  up: DU
+  down: UD
+
+# ---------------------------------------------------------------------------
+# The grid
+# ---------------------------------------------------------------------------
+#
+# Each screen sits at "<row>x<col>". Row increases DOWNWARD, so "-1x0" is above
+# "0x0" and "1x0" is below it. You start at "0x0".
+#
+# QUOTE THE COORDINATE. Unquoted, YAML reads 0x0 as the hexadecimal number 0.
+#
+# Coordinates are ordering, not slots: only their sort order matters, so "0x1"
+# and "0x5" are interchangeable. You never have to count how many screens a
+# socktop group produces in order to place the thing next to it.
+#
+# This example is the rack display:
+#
+#                          unifly            -1x0
+#                            |
+#       4 Pis  <-> orangepi + trixie         0x0, 0x1
+#                            |
+#                       uptime kuma          1x0
+
+screens:
+  # Swipe UP from anywhere in row 0 to reach this.
+  - at: "-1x0"
+    type: unifly
+
+  # One cell, five screens: the four Pis tiled, then each Pi zoomed in turn.
+  - at: "0x0"
+    type: socktop
+    socktop_group: [rpi-master, rpi-worker-1, rpi-worker-2, rpi-worker-3]
+    layout: tiled
+
+  # Swipe forward past the last Pi to arrive here. socktop_group also accepts a
+  # comma-separated string, and layout takes any tmux layout name.
+  - at: "0x1"
+    type: socktop
+    socktop_group: "orangepi, trixie"
+    layout: even-vertical
+
+  # Swipe DOWN from row 0. Swiping back up returns to the exact host you left.
+  - at: "1x0"
+    type: uptime-kuma-status
+    url: https://status.wittyoneoff.com/status/wittyoneoff
+
+  # Anything else you want on a screen. `command` works on any type, as an
+  # override; for `generic` it is the whole definition.
+  #
+  # - at: "1x1"
+  #   type: generic
+  #   title: logs
+  #   command: journalctl -f -u k3s-agent