Add issues #25, #26, #27; update #7 and #22 statuses

- #25: $VAR expansion in commands
- #26: Shell abbreviations and user-extensible builtins
- #27: $(cmd) subcommand syntax
- #22: Updated with implementation details (in progress)
- #7: Standardize status label

issues/25-envvar-expansion-in-commands.md

@@ -0,0 +1,51 @@
+# 25 — Environment variable expansion in commands
+
+**Status:** open
+
+## Problem
+
+`$VAR` syntax works in Lua expressions but not inside commands:
+
+```lua
+print($PATH)        -- works: $PATH is lexed as TK_ENVVAR, expanded via getenv()
+!echo $PATH         -- broken: $PATH is kept as literal text, passed unexpanded
+```
+
+The same applies to backtick commands:
+
+```lua
+local r = `echo $HOME`   -- $HOME is literal, not expanded
+```
+
+## Why it happens
+
+The lexer has two separate paths for `$`:
+
+1. **In Lua code** (`llex.c:667`): `$NAME` → `TK_ENVVAR` token → compiled to `getenv("NAME")` call
+2. **In command mode** (`llex.c:518`): `$` without `{` is saved as a literal character in the command string buffer
+
+Only `${expr}` interpolation works in commands — it enters a Lua expression context and returns the result inline. Bare `$NAME` is passed through verbatim.
+
+Since commands are executed via `fork`/`exec` (not through `/bin/sh`), there is no shell to expand `$PATH` at runtime either.
+
+## Expected behavior
+
+`$VAR` should expand in commands the same way it does in Lua expressions:
+
+```lua
+!echo $HOME          -- should print /Users/nik
+!echo $PATH          -- should print the PATH value
+local r = `echo $HOME`  -- r.stdout should contain /Users/nik
+```
+
+## Workaround
+
+Use `${expr}` interpolation:
+
+```lua
+!echo ${$HOME}
+```
+
+## Possible fix
+
+In `read_command_body()` (`llex.c:518`), when `$` is followed by an identifier, emit the current command fragment and produce a `TK_ENVVAR`-equivalent expansion inline — similar to how `${expr}` already splits the command string to insert interpolated values.