keys: one table drives dispatch, help, footers, the rail and the wiki

keymap.ts lists every key with its context, action and help line.
actions.ts holds what each one does, typed against the table so a key
without an action, or an action without a key, does not compile.
modes.ts stacks the contexts (always > sheet > drawer > workspace >
writing > focused tile > special > global) and writes the two-key
pending logic once. App.svelte's 480-line onkeydown is now one call.

Help, the panel footers (a shared Keys component), the rail's keycaps
and Commands.md all read the table; the wiki gains the card and
scratchpad key tables.

One fix on the way: Ctrl-S in the editor no longer saves twice, which
could make the second save fail as "changed somewhere else".

scripts/wiki.ts

@@ -4,8 +4,8 @@
  * docs/wiki holds the pages. Three of them are not written by hand but read
  * out of the code, so they cannot drift from it:
  *
- * - Commands.md, from the keys in Help.svelte and the commands in commands.ts,
- *   the same lists `:help` draws;
+ * - Commands.md, from the keymap in keymap.ts and the commands in
+ *   commands.ts, the same lists `:help` draws;
  * - Configuration.md, from the comments and values in .env.example;
  * - API.md, from the API section of README.md.
  *
@@ -17,6 +17,7 @@
  */
 import { cpSync, existsSync, mkdirSync, readdirSync, readFileSync, rmSync, writeFileSync } from 'node:fs'
 import { join, resolve } from 'node:path'
+import { rows, sections, type Section } from '../web/src/lib/keymap'
 
 const root = resolve(import.meta.dir, '..')
 const pages = join(root, 'docs/wiki')
@@ -45,17 +46,11 @@ const code = (text: string) => (text.includes('`') ? `<code>${cell(text).replace
 
 // --- Commands.md ---------------------------------------------------------------
 
-function keyTable(source: string, name: string): string {
-  const start = source.indexOf(`const ${name}: [string, string][] = [`)
-  if (start < 0) throw new Error(`Help.svelte has no ${name}`)
-  const body = source.slice(start, source.indexOf('\n  ]', start))
-  const pairs = [...body.matchAll(new RegExp(`\\[${STRING}, ${STRING}\\]`, 'g'))].map(([, key, description]) => [unquote(key), unquote(description)])
-  if (pairs.length === 0) throw new Error(`Help.svelte: ${name} is empty`)
-  // `rule` is not a key but the sentence the help column starts with.
-  const rule = pairs.find(([key]) => key === 'rule')
-  const rows = pairs.filter(([key]) => key !== 'rule').map(([key, description]) => `| ${code(key)} | ${cell(description)} |`)
-  const table = ['| key | what it does |', '| --- | --- |', ...rows].join('\n')
-  return rule ? `${rule[1][0].toUpperCase()}${rule[1].slice(1)}.\n\n${table}` : table
+function keyTable(section: Section): string {
+  const entry = sections.find((candidate) => candidate.section === section)!
+  const table = ['| key | what it does |', '| --- | --- |', ...rows(section).map(({ key, description }) => `| ${code(key)} | ${cell(description)} |`)].join('\n')
+  // A rule is not a key but the sentence the help column starts with.
+  return entry.rule ? `${entry.rule[0].toUpperCase()}${entry.rule.slice(1)}.\n\n${table}` : table
 }
 
 interface Spec {
@@ -116,7 +111,7 @@ function commandsPage(): string {
   })
 
   return (
-    generated('web/src/lib/Help.svelte and web/src/lib/commands.ts') +
+    generated('web/src/lib/keymap.ts and web/src/lib/commands.ts') +
     `# Keys and commands
 
 Everything here is also on \`?\` (\`:help\`) inside the app, which draws the same
@@ -129,15 +124,23 @@ arguments and \`↑\` / \`↓\` recall earlier lines.
 
 ### Browsing and reading
 
-${keyTable(help, 'keys')}
+${keyTable('keys')}
 
 ### On a board
 
-${keyTable(help, 'boardKeys')}
+${keyTable('board')}
+
+### On the back of a card
+
+${keyTable('card')}
 
 ### In the agenda
 
-${keyTable(help, 'agendaKeys')}
+${keyTable('agenda')}
+
+### In the scratchpad
+
+${keyTable('scratch')}
 
 ## Commands