Patch headers and comments: concise

Document the patch calling convention once in lib/default.nix; patch
headers say what, target, hook, state and contracts. Comments only, no
code changes.

modules/lib/default.nix

@@ -1,13 +1,23 @@
-# Shared helpers of the runtime Steam UI patches.
-# - finders.js: signature-based lookup of webpack modules/exports and React
-#   fibers (no module ids or minified names);
-# - signatures.json: the signatures the patches use, per patch, also read by
+# Shared helpers of the runtime Steam UI patches:
+# - finders.js: signature-based lookup of webpack modules/exports and fibers;
+# - signatures.json: per-patch signatures, also read by
 #   scripts/check-signatures.mjs (run it after a Steam update);
-# - hooks.js: shared method hooks (one wrapper per method for all patches,
-#   e.g. the SteamVR dashboard mailbox's SendMessage);
-# - mkPatch: turns a patch written as a function expression
-#   `(find, sigs, opts, hooks) => …` into the single expression the injectors
-#   evaluate: (<patch>)(<finders.js>, <signatures>, <opts>, <hooks.js>).
+# - hooks.js: one shared wrapper per hooked method (e.g. SendMessage);
+# - mkPatch: builds the expression the injector evaluates.
+#
+# Patch convention: a patch file is a function expression
+#   (find, sigs, opts, hooks) => <status string or Promise of one>
+# (trailing parameters may be omitted), called as
+#   (<patch>)(<finders.js>, <signatures>, <opts>, <hooks.js>)
+# with find = lib/finders.js, sigs = its module signatures, opts = the JSON
+# options from its module, hooks = lib/hooks.js. The injector re-evaluates it
+# on every new JS context and periodically, so it must be idempotent: keep
+# state on a window.__sfui* global (or on the wrapped function), return
+# "unchanged" when already applied (not logged) and tear down/re-apply when
+# its VERSION or options differ. Bump VERSION whenever the patch code changes.
+# A matching unpatch.js (plain expression) reverts it when the service stops.
+# Patches needing none of the arguments may be plain expressions without
+# mkPatch (e.g. launcher-menu/order).
 { pkgs }:
 let
   sigFile = builtins.fromJSON (builtins.readFile ./signatures.json);
@@ -17,8 +27,8 @@ in {
   hooks = ./hooks.js;
 
   # name: file name (and default signatures entry); src: the patch file;
-  # signatures: module signatures passed as `sigs` (default: the entry `name`
-  # of signatures.json, else none); opts: JSON-serialisable options.
+  # signatures: `sigs` (default: signatures.json entry `name`, else none);
+  # opts: JSON-serialisable options.
   mkPatch = { name, src, signatures ? sigFile.patches.${name}.modules or { }, opts ? { } }:
     pkgs.writeText "${name}.js" ''
       (${builtins.readFile src}