port: delete exit_ramp_units, invert the format's own rule, and guard a scale-0 leaf

FOUR THINGS, and the first is what MISSION section 3 calls the measure of
progress.

DELETED `exit_ramp_units` AND `exit_ramp_seconds`. They were authored because the
disc had no time slot on a group's final keyframe, so the ramp into it was the
one unknown duration per screen. Under the corrected record layout that keyframe
does not exist -- a group is an 8-byte header then frames x {u32 time; 36-byte
pose} and every pose is timed. VERIFIED DEAD BEFORE DELETING: setting it to 9999
(166 s) moved the boot's transitions by 0.04 s, which is wall-clock jitter, and
both uses in ScreenView are gated on a condition that no longer fires on any of
the export's 866 keyframes.

INVERTED THE FORMAT'S OWN RULE. `check.rs` enforced "the final keyframe has no
`t`; the disc has no time slot there" and FORMAT.md stated it. Both are now
backwards, and the validator fired 150 times on a re-export. I had not run
`check` between pinning the tag and measuring against the oracle -- the pixel
harness was green while the format validator was failing on every screen with a
multi-keyframe group. A correctness harness does not replace a format one; they
fail at different layers.

GUARDED A SCALE-0 LEAF, which the Decoder hit in its own renderer: its leaf
branch marked the element drawn unconditionally while the blit returned early on
zero scale, so a scale-0 leaf suppressed its parent and blanked the element --
live on all four loading screens. This port did not have the bug only because
authored/rendering.json happens not to list pgloading_loop5. That is an accident
of a gate written for another reason, not a defence, so `_draw_leaf` now reports
whether it drew and `_draw` falls back to the parent.

ISOLATED THE PACING QUESTION rather than leaving it as a suspected regression.
Legacy association: publisher 4.70 agrees, developer 3.92 DIFFERS. Corrected:
publisher 4.26 DIFFERS, developer 3.62 agrees. Both misses are ~0.03 s outside a
composite bound. The association traded which screen is marginally out; it did
not regress the pacing.

Bumped the pin c -> d for the parser and audio changes. Its headline renderer
change does not reach this port: sylpheed-cli builds from the workspace crate.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01N7FiFFFwbvG2uxdcEh8HyF

authored/timing.json

@@ -24,28 +24,6 @@
   "Also HANDOFF Q1, and part of the same measurement: the fade lands on the",
   "linear value at every one of the seven sampled frames, so there is no ease."
  ],
- "exit_ramp_seconds": 0.4,
- "exit_ramp_why": [
-  "HANDOFF Q7 + the RE agent's 2026-08-29 answer. MEASURED, not on the disc.",
-  "",
-  "Every element of a screen ends on exactly ONE untimed keyframe, so there is",
-  "exactly one unknown duration per screen -- the ramp INTO that final keyframe.",
-  "This is that duration. ~0.4 s, which is 24 units at 60 units/s.",
-  "",
-  "The alternative readings were tested and refuted. It is not a black quad laid",
-  "over a frozen screen: under that model a black rect scales every region by the",
-  "same 1-alpha, so the button-region / background-region brightness RATIO would",
-  "be constant through the fade. Measured on the RE agent's filmstrip it falls",
-  "6.495 -> 5.574 -> 3.105 -> 2.125 -> 1.935, a 3.4x monotonic drop. The screen",
-  "itself plays out: pteff00.prm ramps to opaque black while the button labels,",
-  "ptmsg, pteff10 and pteff12 all ramp to transparent, and ptframe1/2 hold.",
-  "",
-  "REACH, quoted from the RE agent rather than smoothed over: the filmstrip is",
-  "downsampled and the button region contains some background, so this pins the",
-  "DIRECTION, not 0.4 s to +/-0.05 s, and it is one transition pair. Treat the",
-  "number as approximate and the model as established."
- ],
- "exit_ramp_units": 24,
  "dwell_seconds": null,
  "dwell_why": [
   "NOT SET, and not needed. A screen's dwell is its OWN keyframe group: the",
@@ -112,5 +90,30 @@
     "in the same frame, or a loop flag decoded on the disc."
    ]
   }
- }
+ },
+ "exit_ramp_deleted_why": [
+  "DELETED 2026-08-29, and the deletion is the point.",
+  "",
+  "`exit_ramp_seconds` (~0.4 s) and `exit_ramp_units` (24) were AUTHORED because",
+  "the disc had no time slot on a group's final keyframe, so the ramp into it was",
+  "the one unknown duration per screen. Under the corrected record layout",
+  "(formats-pin-2026-08-29c onward) there IS no untimed keyframe -- a group is an",
+  "8-byte header then frames x {u32 time; 36-byte pose}, so every pose is timed",
+  "including the last. The unknown the constant stood in for does not exist.",
+  "",
+  "MISSION section 3: 'When the RE agent later decodes something you had",
+  "authored, delete the authored entry and let the exporter emit it. That",
+  "deletion is the measure of progress.'",
+  "",
+  "VERIFIED DEAD BEFORE DELETING, not assumed: setting it to 9999 (166 seconds)",
+  "changed the boot's transitions by 0.04 s -- wall-clock jitter, not a 166 s",
+  "ramp. Both of its uses in ScreenView were gated on `not last_frame.has('t')`,",
+  "which no longer fires on any of the export's 866 keyframes.",
+  "",
+  "The measurement it recorded is not lost: HANDOFF Q7's ~0.4 s fade-out and the",
+  "0.17-0.23 s black hold are still measured facts, and the hold is still used --",
+  "`tools/port/verify-dwell` compares a transition INTERVAL against the oracle's",
+  "visible SPAN plus that hold. What is deleted is the port's need to invent a",
+  "duration the disc now states."
+ ]
 }