fix(install): treat non-archive single file gracefully in ziextract.

Change `ziextract` when no extractor case matches and no explicit type was passed (-z $ext), file is treated as plain single file with info message
`'<file>' is not an archive — keeping it as a plain file.` plus chmod a+x. The existing exec-bit collection then picks it up, sets REPLY for --move, prints normal
success. Error message retained for explicit bogus types (ziextract file bogus-type). One iteration mid-verify: dropped -- from chmod — BSD/macOS chmod rejects it (chmod: --:
No such file or directory).

Why it broke: commit 1334994f (PR #771) made +x detection archive-exec-bit-only. Bare gh-r binaries arrive over HTTP with 644 and no extension => no extractor, no exec bit →
error branch. Pre-#771, file(1) detection covered this case.

Tests (tests/ices.zunit): two new — plain-file success path (asserts no error, message present, file executable) and bogus-explicit-type error
retention. Suite 16/16, including #771's ziextract-permissions. Regression-validated: plain-file test fails 15/16 with fix stashed.

Signed-off-by: Vladislav Doster <mvdoster@gmail.com>

tests/ices.zunit

@@ -82,6 +82,27 @@
   assert $output contains 'ERROR'
   assert $output contains "doesn't exist"
 }
+@test 'ziextract plain single file (not an archive)' {
+  # A bare gh-r-style release binary: no "unrecognized archive" error,
+  # the file is kept as-is and marked executable.
+  local workdir=$(mktemp -d)
+  printf '#!/bin/sh\necho jq\n' > "$workdir/jq-macos-arm64"
+  _zi_extract_plain() { cd "$workdir" && ziextract jq-macos-arm64 }
+  run _zi_extract_plain
+  assert $state equals 0
+  assert $output does_not_contain "didn't recognize archive type"
+  assert $output contains 'not an archive'
+  assert "$workdir/jq-macos-arm64" is_executable
+  rm -rf "$workdir"
+}
+@test 'ziextract still errors on unrecognized explicit type' {
+  local workdir=$(mktemp -d)
+  printf 'plain text\n' > "$workdir/somefile"
+  _zi_extract_bogus() { cd "$workdir" && ziextract somefile bogus-type }
+  run _zi_extract_bogus
+  assert $output contains "didn't recognize archive type"
+  rm -rf "$workdir"
+}
 @test 'ziextract plain (no flattening)' {
   # extract'' → ziextract with no flags: directory structure is preserved
   local workdir=$(mktemp -d)

zinit-install.zsh

@@ -1754,6 +1754,17 @@ ziextract() {
         unfunction -- →zinit-extract →zinit-check
     } else {
         integer warning=1
+        # Not an archive and no explicit type claimed — treat as a plain single
+        # file (e.g. a bare gh-r release binary). HTTP downloads carry no exec
+        # bit, so mark the file executable and let the execs collection below
+        # pick it up and report success.
+        if [[ -z $ext ]] {
+            warning=0
+            (( !OPTS[opt_-q,--quiet] )) && \
+                +zi-log "{info}[{pre}ziextract{info}]{rst}" \
+                    "\`{file}${file}{rst}' is not an archive — keeping it as a plain file."
+            command chmod a+x "$file"
+        }
     }
     unfunction -- .zinit-extract-wrapper