The TinyGo build, and stop advertising a demo that is not in it

docs/tinygo/desktop.wasm carries the twelve new animations: 8.11 MB to
10.17 MB, two megabytes for the lot, against 20.6 MB for the standard Go
build of the same thing. /tinygo/?demo=parrot works now.

The build overlapped a go mod vendor of its own dependency tree, so it was
verified rather than trusted: every new demo name is in the binary and the
parrot renders in a browser. docs/desktop.wasm is rebuilt too and differs
from the committed copy by 115 bytes, all of them in the build-ID region at
the head of the file; the payload is byte-identical.

And a bug this turned up. cmd/gendemos imported demos/markdown
unconditionally while cmd/desktop imports it only under -tags tuimarkdown, so
the generated table listed a demo the shipped binary does not contain and
?demo=markdown has been answering "no demo called markdown". pterm never had
the problem because its build tag is on the demo package itself, which makes
it unimportable rather than merely unimported.

The fix puts gendemos behind the same tag: the default run now writes 42
demos and -tags tuimarkdown writes 43. A table generated from a different
build than the one that ships is a table that lies, and this one had been
lying since the demo was tagged out.

Author: 0pcom

README.md

@@ -96,7 +96,11 @@ at startup — so a link to one costs nothing to serve and there is no per-demo
 build. The full-page view has no chrome at all: it should look like the terminal
 it would run in, and the browser already has a back button.
 
-`pterm` is not listed: it needs `-tags pterm`, see `shims/`.
+`pterm` is not listed: it needs `-tags pterm`, see `shims/`. Neither is
+`markdown`, which needs `-tags tuimarkdown` — glamour and chroma are a couple
+of megabytes for one demo. Build gendemos with the same tags as the binary and
+both appear; the table describes the build it was generated from, never a
+build nobody ships.
 
 <!-- BEGIN DEMOS -->
 | demo | shape | what it is |
@@ -121,7 +125,6 @@ it would run in, and the browser already has a back button.
 | [`lavalamp`](https://tuiwasm.magnetosphere.net/?demo=lavalamp) | screen | wax that heats, rises, cools and sinks |
 | [`life`](https://tuiwasm.magnetosphere.net/?demo=life) | screen | Conway's life, colored by how long a cell has lived |
 | [`lightning`](https://tuiwasm.magnetosphere.net/?demo=lightning) | screen | a branching discharge: leader, return stroke, afterglow |
-| [`markdown`](https://tuiwasm.magnetosphere.net/?demo=markdown) | text | glamour + chroma — rendered markdown, highlighted code |
 | [`matrix`](https://tuiwasm.magnetosphere.net/?demo=matrix) | screen | falling columns of glyphs |
 | [`maze`](https://tuiwasm.magnetosphere.net/?demo=maze) | screen | a maze carved by backtracking, then solved |
 | [`metaballs`](https://tuiwasm.magnetosphere.net/?demo=metaballs) | screen | blobs that bulge and merge as they approach |

cmd/gendemos/main.go

@@ -34,7 +34,6 @@ import (
 	// eventually draw into is js/wasm.
 	_ "github.com/0magnet/tuiwasm/demos/anim"
 	_ "github.com/0magnet/tuiwasm/demos/charts"
-	_ "github.com/0magnet/tuiwasm/demos/markdown"
 	_ "github.com/0magnet/tuiwasm/demos/proxima"
 	_ "github.com/0magnet/tuiwasm/demos/proxima2"
 	_ "github.com/0magnet/tuiwasm/demos/styles"

cmd/gendemos/markdown.go

@@ -0,0 +1,19 @@
+//go:build tuimarkdown
+
+// Package main cmd/gendemos/markdown.go
+//
+// The markdown demo's registration, behind the same tag cmd/desktop puts it
+// behind.
+//
+// Without this the table listed a demo the shipped binary does not contain:
+// gendemos imported demos/markdown unconditionally and saw it register, while
+// cmd/desktop imports it only under -tags tuimarkdown, so every published
+// ?demo=markdown link answered "no demo called markdown". pterm never had the
+// problem because its build tag is on the demo package itself, which makes it
+// unimportable rather than merely unimported.
+//
+// The rule this restores: gendemos must be built the same way as the thing it
+// documents, so the table cannot describe a build nobody ships.
+package main
+
+import _ "github.com/0magnet/tuiwasm/demos/markdown"