re: the inverse sweep -- 41 env vars read, 22 undocumented, none in the UI path

sylpheed-port inverted my documented->exists sweep into parsed->documented and
found three live undocumented flags, with the framing that a capability existing
only in an 11 000-line record is, to a reader of the interface, a capability that
does not exist. The mirror on my side is env vars the CODE reads, checked against
the docs. Like theirs it enumerates, so it completes rather than samples.

41 read by crates/, 19 documented, 22 not. The 22 split cleanly: 7 are read only
in examples/ (per-example filters and dump paths, reachable only by editing an
example's command line), and 15 are read in src/ -- live capabilities of the
library and CLI. Ten are mesh/3D toggles and five are XPR_* texture-decode
toggles.

FOR THE PORT: none of the 15 is in the UI path. Every env var ui_layout.rs and
the screen commands read is documented -- SYLPHEED_REST_RULE and
SYLPHEED_KF_TIME_LEGACY. The menu lane is clean in this direction. But the five
XPR_* are texture-decode toggles and the port consumes textures, so if a sprite
comparison ever disagrees those are the knobs and they are invisible from the
interface.

LIMIT, stated rather than glossed: I verified NONE of the 15 end to end.
`texture export` takes a loose file and the disc keeps its textures inside paks,
so the check cost more than the answer was worth here. That matters because the
port found --no-hold parsed, documented AND INERT under an interaction with
--time: "parsed and reachable" is not "works". The honest claim is that 15
undocumented env vars are READ, not that 15 capabilities exist.

METHOD: sweep the surface in both directions, and note that both directions
enumerate and therefore complete rather than sample -- rare enough in that file to
be worth preferring when available -- while neither establishes that the thing
works.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Wuu56cE8vJGTBtn1ppsk8v

docs/re/METHOD.md

@@ -494,6 +494,21 @@ agent's loop prompt, i.e. nowhere durable. See [`README.md`](README.md) for the
   **author** a value that is decoded. **When sweeping for stale text, rank
   instructions above descriptions**: a wrong description misleads a reader, a wrong
   instruction produces a wrong *result* that looks like evidence.
+  📌 **Sweep the surface in BOTH directions.** Documented → does it exist, and
+  **parsed → is it documented**. `sylpheed-port` ran the second and found three
+  live undocumented flags, one of which (`--no-hold`) plays a screen past its rest
+  — *"a capability that exists only in an 11 000-line record is, to anyone reading
+  the interface, a capability that does not exist."* The mirror here: **41 env vars
+  read by `crates/`, 22 undocumented** — 7 example-only scratch, **15 live in
+  `src/`**, all in the mesh and texture lanes, none in the UI path
+  ([`data/env-var-surface.txt`](data/env-var-surface.txt)). Both directions
+  enumerate, so both **complete rather than sample** — which is rare enough in this
+  file to be worth choosing sweeps of that shape when one is available.
+  ⚠️ **And neither direction establishes that the thing WORKS.** They documented
+  `--no-hold` and it was inert under an interaction with `--time` — caught only by
+  running the example. I verified none of my 15 end to end and have said so rather
+  than implying coverage.
+
   📌 **And rank SILENT instructions above LOUD ones** (`sylpheed-port`'s
   refinement, from finding all of theirs were the loud kind): a wrong path errors
   out and announces itself; **an inert environment variable returns a clean, wrong

docs/re/data/env-var-surface.txt

@@ -0,0 +1,37 @@
+# The environment-variable surface, both directions. 2026-08-30.
+#
+# sylpheed-port swept documented -> parsed and found three live-but-undocumented
+# flags, noting that a capability documented only in an 11 000-line record is, to
+# anyone reading the interface, a capability that does not exist. This is the
+# mirror on my side: every env var the CODE reads, checked against the docs.
+# Like theirs it ENUMERATES, so it completes rather than samples.
+#
+#   41 environment variables read by crates/
+#   19 documented
+#   22 NOT documented, splitting cleanly:
+#
+#      7 read only in examples/ -- per-example output filters and dump paths.
+#        KF_SHOW, MAX_PAD, OUT_DIR_X, SUPPRESS_SUBSTR, SYLPH_RAW,
+#        VOICE_CHUNK_DUMP, DUMP_XPR_DIR
+#        Scratch. Reachable only by editing an example's command line.
+#
+#     15 read in src/ -- LIVE capabilities of the library and CLI:
+#        mesh / 3D   XCOLORSUB XDUMPHDR XDUMPVERT XMESHDBG XMIRROR XNODEDUMP
+#                    XNODEXFORM XONLYSUB XSPANHIDE XSPANONLY
+#        texture     XPR_FORCE_ENDIAN XPR_NO_BC_DWORD_SWAP XPR_NO_DETILE
+#                    XPR_NO_ENDIAN XPR_RES_INDEX
+#
+# ✅ FOR THE PORT: none of the 15 is in the UI path. Every env var ui_layout.rs
+# and the screen commands read is documented -- SYLPHEED_REST_RULE and
+# SYLPHEED_KF_TIME_LEGACY. The menu lane is clean in this direction.
+#
+# ⚠️ The five XPR_* are TEXTURE DECODE toggles and the port consumes textures. If
+# a sprite comparison ever disagrees, these are the knobs, and they are invisible
+# from the interface.
+#
+# 🔴 LIMIT, stated rather than glossed: I verified NONE of the 15 end to end.
+# `texture export` takes a loose file and the disc keeps its textures inside paks,
+# so the check cost more than the answer was worth in this iteration. That matters
+# because sylpheed-port found `--no-hold` PARSED, DOCUMENTED and INERT under an
+# interaction with `--time`: "parsed and reachable" is not "works". So the honest
+# claim is that 15 undocumented env vars are READ, not that 15 capabilities exist.