feat(annotate): lean GEPA-aligned subtask segmentation prompt

Replace the verbose, label-heavy segmentation prompt with a lean
adaptation of the blog's GEPA-found completed_events_duration_prior
recipe: focus on completed manipulation events, explicit no-split /
no-merge rules, a 2-10s duration prior, and an instruction to prioritize
temporally correct boundaries over label wording. The previous prompt
over-weighted label guidance, which traded away boundary precision.

Co-authored-by: Cursor <cursoragent@cursor.com>

src/lerobot/annotations/steerable_pipeline/prompts/plan_subtasks.txt

@@ -1,61 +1,28 @@
-You are annotating a teleoperated robot demonstration shown as
-timestamped contact sheets (each tile has its time in seconds burned
-into the top-left corner). The operator's goal was: "{episode_task}"
+Reconstruct the sequence of manipulation events in this robot
+demonstration from the timestamped contact sheets (each tile has its time
+in seconds burned into the top-left corner). The operator's goal was:
+"{episode_task}"
 
-{observation_block}Reconstruct the sequence of COMPLETED manipulation events the robot
-performs, in chronological order. Output one segment per event with a
-[start, end] time in seconds and a short action label.
-
-GROUNDING — read first, it overrides everything below:
-- Label ONLY events you can SEE in the frames. The instruction is the
-  goal; the VIDEO is the ground truth for what actually happened.
-- Do NOT invent, anticipate, or pad steps that are not shown.
-
-Granularity — segment by completed events, not by motion:
-- Start a NEW segment whenever the world state changes: an object is
-  grasped, lifted, transported, placed, or released; a held object
-  changes; a drawer/door/lid/container opens or closes; contents move
-  between containers (poured); a tool starts or stops acting on a
-  surface. Watch the gripper open/close transitions — they usually mark
-  boundaries.
-- Do NOT split approach, reach, grasp adjustment, small repositioning,
-  hesitation, or retreat into their own segments. Fold each into the
-  event it belongs to (the approach is part of the pick; the retreat is
-  part of the place).
-- Do NOT merge separate completed events. Each distinct pick, place,
-  open, close, pour, push, wipe, or insert is its own segment, even when
-  they repeat on different objects or locations.
-- Most segments last 2-10 seconds. Shorter segments are okay ONLY for
-  fast pick / place / open / close / release events. Never emit a
-  segment shorter than {min_subtask_seconds} seconds; merge a too-short
-  candidate into its neighbour instead.
-- Skip idle time, pure camera motion, and tiny hand jitter.
-
-Labels — short imperative phrases:
-- One concise command naming the action and the manipulated object, e.g.
-  "pick up the red cup", "put the cup on the shelf", "open the top
-  drawer", "pour water into the glass", "insert the plug into the
-  socket".
-- Include source, destination, side, direction, or the final
-  open/closed state when it is visible and central to the event.
-- Prefer these verbs (extend only when none fits): pick up, put, place,
-  push, pull, turn, press, open, close, pour, insert, wipe, stack.
-  Disambiguate by what you SEE:
-    * STACK vs PUT: object placed ON TOP OF another object -> "stack".
-    * INSERT vs PUT: object pushed INTO a fitted slot/hole/socket -> "insert".
-    * PICK UP vs PUT (direction): gripper CLOSES and object moves WITH
-      the hand -> "pick up"; gripper OPENS and object stays -> "put".
-    * POUR vs PUT: source is tilted and contents flow -> "pour".
-- Use the exact object nouns implied by the task; stay consistent across
-  the episode (don't switch "cube" to "block").
-- Write imperative commands, never third person ("the robot ..."), and
-  drop articles/adverbs.
-
-Timing:
-- Use the burned-in timestamps to set start and end. Boundaries should
-  land on or near a printed time, and every [start, end] must lie within
-  [0.0, {episode_duration}] seconds, be non-overlapping, and cover the
-  episode in order.
+{observation_block}Rules:
+- Segment only completed robot manipulation events, not every visible
+  movement.
+- Good boundaries happen when a held object changes, an object is placed
+  or released, a tool starts or stops changing a surface, a
+  container/door/lid opens or closes, or contents move between containers.
+- Do not split approach, grasp adjustment, small repositioning, or retreat
+  unless the world state changes.
+- Do not merge separate pick / place / open / close / pour / wipe events
+  when they complete different states.
+- Most segments should be 2-10 seconds. Shorter segments are okay only for
+  fast pick, place, open, close, or release events. Never emit a segment
+  shorter than {min_subtask_seconds} seconds.
+- Use the visible burned-in timestamps for start and end. Every [start,
+  end] must lie within [0.0, {episode_duration}] seconds, be
+  non-overlapping, and cover the episode in chronological order.
+- Give each segment a short imperative label naming the action and the
+  manipulated object (add destination, side, direction, or final
+  open/closed state when visible), but prioritize temporally correct
+  boundaries over label wording.
 - Emit at most {max_steps} segments.
 
 Output strictly valid JSON of shape: