chore(training): close Stage 5 by human override, re-derive its air-touch gate

productive_air_touch_episode_fraction's 0.02 floor was set as an explicit
PROVISIONAL guess (see the Round 10 comment in generation5.py) with
instructions to re-derive it from attempt 1's measured tail. That never
happened: five more Stage-5 attempts (20260824 through -retry4) ran against
the unchanged number, reading 0.00004/0.00006/0.00002/0.00018/0.00006 -- no
trend, ~500x under the floor -- while every other gate passed comfortably and
each attempt beat the Stage-4 reference head-to-head. Direct TensorBoard
query of retry4's full run confirms the touches are real and stable, just
rare (22/1000 rollout-logging windows registered one touch in the
~100-episode buffer), so further identical retries were not going to close a
500x gap.

Lowered the floor to 0.00002 (the minimum of the five measured attempts),
same as-under-the-observed-band logic the Stage-4 override used for
goal_rate. Flipped retry4's log entry to decision: pass with a
decision_override block (same pattern as the Stage-4 override) and advanced
generation5_state.json to Stage 6 attempt 0. Documented in TRAINING.md and
flagged Stage 6's own 0.015 floor for the same metric as equally unvalidated.

training/generation5.py

@@ -396,13 +396,34 @@ STAGES = [
             # form asks the question the bar actually means: did this episode
             # contain a productive aerial at all?
             #
-            # 0.02 is PROVISIONAL and deliberately low. There is no measured
-            # baseline to derive it from — the metric reads 0.0 on retry2's
-            # checkpoint — and setting an unachievable bar from arithmetic
-            # rather than measurement is precisely what cost this stage nine
-            # attempts. Treat attempt 1 as establishing the real distribution
-            # and re-derive this from its tail before trusting it as a gate.
-            "rollout/productive_air_touch_episode_fraction": 0.02,
+            # Round 11 (2026-08-29): the 0.02 above was never re-derived, and
+            # the comment that set it said explicitly to do that after
+            # attempt 1. Five more attempts (20260824 through -retry4) ran
+            # against it unchanged: 0.00004, 0.00006, 0.00002, 0.00018,
+            # 0.00006 -- no trend, all within one order of magnitude of each
+            # other and roughly 500x under the floor. rollout/air_touch_
+            # fraction over retry4's full run confirms this is real signal
+            # rather than a broken metric (22 of 1000 rollout-logging windows
+            # registered exactly one aerial touch in the ~100-episode SB3
+            # buffer) -- just a rare event at this training-time drill mix,
+            # not a growing one. Every other gate cleared comfortably on all
+            # five attempts (retry4: goal_rate 0.796 vs 0.72, upright 0.778
+            # vs 0.40, forward_motion 0.493 vs 0.20) and every attempt beat
+            # the Stage-4 reference head-to-head (retry4: 53-26-21, sides
+            # 29-11 / 24-15). Lowered to 0.00002 -- the minimum of the five
+            # measured attempts, same "just under the observed band" logic
+            # Stage 4's own override used for goal_rate (see TRAINING.md) --
+            # so this floor now tests for regression against real behaviour
+            # instead of an unvalidated guess. retry4 closed Stage 5 by
+            # human override under the corrected floor rather than a sixth
+            # identical retry; see TRAINING.md and generation5_state.json's
+            # decision_override on that entry.
+            #
+            # Stage 6's 0.015 below carries the exact same provisional-guess
+            # problem and has never run a single attempt. Re-derive it from
+            # measured data the same way once Stage 6 actually produces a
+            # tail -- don't assume it transfers from this number.
+            "rollout/productive_air_touch_episode_fraction": 0.00002,
         },
         "evaluation_goal_rate_floor": 0.75,
         "physical_side_imbalance_ceiling": 0.20,