fix(highlight): PR #116 round 1 — shebang precedence, pinned grammar, env operands

Three review findings, all in builtin/runtime/syntax.lua.

1. [P1] Syntax bypassed extension precedence and grammar availability.
   attach_for_active_buffer resolved `language_for_path or shebang`, but
   language_for_path knows only grammar-backed extensions — so a `.py`
   file opening with `#!/bin/sh` fell through to the shebang and got a
   bash parse tree, and an extensionless `#!/usr/bin/env python3` script
   dispatched "python" (no grammar) and raised "unknown language". A new
   resolve_active_language walks the full precedence chain — grammar
   extension -> LSP filetype map -> shebang — consulting the shebang only
   when the extension is unrecognized (a recognized non-grammar extension
   like .py is authoritative). Dispatch is then gated on
   pmacs.parse._has_language(lang), so grammarless languages are skipped
   silently. The extension parts stay keyed on buf:name() (unchanged from
   before), so path-less buffers that resolve a grammar by name — e.g.
   generated markdown buffers — are unaffected.

2. [P2] Editing an open script's shebang left parsing/highlighting stale.
   The after-edit path re-sniffed the mutable shebang: sh -> python
   raised "unknown language" while leaving the old bash tree, and
   sh -> lua swapped the parse tree under a highlight overlay still
   holding the original grammar's query. Reparse now uses the language
   pinned at first attach (parse_lang_by_buffer), never re-resolving —
   a language change needs a close/reopen, as it does for extensions.

3. [P2] `env` options with operands were mistaken for interpreters.
   `#!/usr/bin/env -u FOO python3` skipped `-u` but took `FOO`. The env
   walk now skips the operand of the operand-consuming GNU-env options
   (-u/--unset, -C/--chdir, -a/--argv0) before selecting the interpreter.
   -S/--split-string stays excluded (its string carries the interpreter).

Tests (bite-verified against pre-fix syntax.lua — each fails without its
fix; scripts/bite HEAD builtin/runtime/syntax.lua):
- m4_shebang_does_not_override_extension now also asserts _has_view is
  false (no bash grammar tree for a `.py` + `#!/bin/sh`), not only the
  LSP language.
- m4_shebang_extensionless_grammarless_language_is_silent — extensionless
  python resolves for LSP, gets no grammar view, and records no error.
- m4_shebang_edit_keeps_pinned_grammar — rewriting a `#!/bin/sh` script's
  shebang to lua keeps the bash tree and reports no error.
- m4_shebang_resolver_maps_interpreters — added the env-operand cases
  (`-u FOO`, `-C /tmp`, combined).

Gates: fmt; clippy -D warnings; m4_acceptance --skip basedpyright; GPU;
git diff --check all green. The only sweep failure is the pre-existing
editor::composition_overhead_under_ten_percent render microbenchmark
(ratio hovers at the 1.10 cutoff; flakes ~1/3 even isolated single-
threaded, already asserted-off on macOS) — a pure-Rust render loop this
Lua-only change cannot touch. Change is Lua-only plus the acceptance
tests.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01YJ9FQ832QwftJXCD9LeFan

builtin/runtime/syntax.lua

@@ -96,11 +96,29 @@ function pmacs.parse.language_from_shebang(buf)
   local base = first:match("([^/]+)$") or first
   if base == "env" then
     base = nil
+    local seen_env = false
+    local skip_next = false
     for tok in rest:gmatch("%S+") do
-      -- Skip the `env` path itself, its flags (`-S`, `--split-string`),
-      -- and inline `VAR=value` assignments; the first bare word left is
-      -- the real interpreter.
-      if tok ~= first and tok:sub(1, 1) ~= "-" and not tok:find("=", 1, true) then
+      if not seen_env then
+        seen_env = true -- the `env` path token itself
+      elseif skip_next then
+        skip_next = false -- the operand consumed by the previous option
+      elseif tok:find("=", 1, true) then
+        -- `VAR=value` env assignment, or a `--long=value` option: both
+        -- self-contained, skip.
+      elseif tok:sub(1, 1) == "-" then
+        -- An option. A few GNU-env short options and their long forms
+        -- consume the *next* token as an operand (`-u NAME`, `-C DIR`,
+        -- `-a NAME`); skip that operand too, or its value is mistaken for
+        -- the interpreter. `-S`/`--split-string` is deliberately absent:
+        -- the string it introduces contains the interpreter, which the
+        -- walk then picks up. An option with an attached operand
+        -- (`-uNAME`) is one self-contained token and needs no skip.
+        if tok == "-u" or tok == "-C" or tok == "-a"
+            or tok == "--unset" or tok == "--chdir" or tok == "--argv0" then
+          skip_next = true
+        end
+      else
         base = tok:match("([^/]+)$") or tok
         break
       end
@@ -116,14 +134,37 @@ end
 -- attach; the kill path clears the entry below if/when it lands.
 local highlighted_buffers = {}
 
+-- Filetype-aware language resolution for the active buffer, in
+-- precedence order: grammar extension → LSP filetype map → shebang. The
+-- shebang is consulted ONLY when the extension is unrecognized (a known
+-- non-grammar extension like `.py` must not fall through to a stray
+-- `#!/bin/sh` and be misparsed as bash). Keyed on `buf:name()` for the
+-- extension parts (matching the historical behavior — path-less buffers
+-- that resolve a grammar by name keep working); the shebang reads buffer
+-- content directly.
+local function resolve_active_language(buf)
+  local name = buf:name()
+  if name then
+    local grammar = pmacs.parse.language_for_path(name)
+    if grammar then return grammar end
+    local ext = name:match("%.([%w_]+)$")
+    local by_ext = ext and pmacs.lsp and pmacs.lsp.filetypes and pmacs.lsp.filetypes[ext]
+    -- A recognized (even non-grammar) extension is authoritative; do not
+    -- consult the shebang for it.
+    if by_ext then return by_ext end
+  end
+  return pmacs.parse.language_from_shebang(buf)
+end
+
 local function attach_for_active_buffer()
   local buf = pmacs.window.buffer()
   if not buf then return end
-  local path = buf:name()
-  if not path then return end
-  local lang = pmacs.parse.language_for_path(path)
-    or pmacs.parse.language_from_shebang(buf)
-  if not lang then return end
+  -- Gate dispatch on `_has_language`: the chain above also resolves
+  -- languages with no grammar (python, javascript), and dispatching one
+  -- would raise "unknown language" (caught, but noise) — and an
+  -- extensionless script must never get a wrong-grammar parse tree.
+  local lang = resolve_active_language(buf)
+  if not lang or not pmacs.parse._has_language(lang) then return end
   pmacs.parse._dispatch(buf, lang)
   -- T M4.3: install the syntax-highlight overlay for this buffer.
   -- Idempotent --- repeated calls for the same buffer are a no-op
@@ -175,10 +216,14 @@ local function reparse_active_buffer_after_edit()
   if not pmacs.parse._has_view(buf) then return end
   local pending = pmacs.parse._pending_edits(buf)
   if not pending or pending == 0 then return end
-  local path = buf:name()
-  if not path then return end
-  local lang = pmacs.parse.language_for_path(path)
-    or pmacs.parse.language_from_shebang(buf)
+  -- Reparse with the language pinned when the view was first attached ---
+  -- never re-resolve from the path or (mutable) shebang. The Rust side is
+  -- "first language wins"; re-sniffing a shebang the user just edited
+  -- would either raise "unknown language" (sh → python) or swap the parse
+  -- tree to a new grammar while the highlight overlay still holds the
+  -- original grammar's query (sh → lua). Language changes need a
+  -- close/reopen, exactly as they do for a renamed extension.
+  local lang = parse_lang_by_buffer[tostring(buf)]
   if not lang then return end
   pmacs.parse._dispatch(buf, lang)
 end

tests/m4_acceptance.rs

@@ -5878,6 +5878,11 @@ fn m4_shebang_resolver_maps_interpreters() {
         ("#!/usr/bin/env bash\n", "bash"),
         ("#!/usr/bin/env python3\n", "python"),
         ("#!/usr/bin/env -S python3 -u\n", "python"),
+        // GNU-env options that consume an operand must not have the
+        // operand mistaken for the interpreter.
+        ("#!/usr/bin/env -u FOO python3\n", "python"),
+        ("#!/usr/bin/env -C /tmp python3\n", "python"),
+        ("#!/usr/bin/env -u FOO -C /tmp node\n", "javascript"),
         ("#!/usr/bin/node\n", "javascript"),
         ("#!/usr/bin/env lua\n", "lua"),
     ] {
@@ -5957,17 +5962,132 @@ fn m4_shebang_does_not_override_extension() {
         ))
         .exec()
         .expect("open .py with a shell shebang");
-    let lang: Option<String> = s
+    // Both the LSP language *and* the grammar decision must respect the
+    // extension: python for LSP, and NO grammar parse view (python has no
+    // grammar) — not a bash tree installed from the `#!/bin/sh` line.
+    // `_has_view` is set synchronously by `_dispatch`, so no pump is
+    // needed; without the precedence fix the shebang would have dispatched
+    // bash and this would be true.
+    let (lang, has_view): (Option<String>, bool) = s
         .lua_host
         .lua()
-        .load("return pmacs.lsp.active_buffer_language()")
+        .load(
+            "return pmacs.lsp.active_buffer_language(),
+                    pmacs.parse._has_view(pmacs.window.buffer())",
+        )
         .eval()
-        .expect("language");
+        .expect("language + view");
     assert_eq!(
         lang.as_deref(),
         Some("python"),
-        ".py extension wins over a #!/bin/sh shebang"
+        ".py extension wins over a #!/bin/sh shebang (LSP)"
     );
+    assert!(
+        !has_view,
+        ".py file must not get a grammar parse view from a #!/bin/sh line"
+    );
+}
+
+/// Finding-1 gate: an extensionless `#!/usr/bin/env python3` script
+/// resolves to python for LSP, but python has no grammar — syntax must
+/// skip it *silently*. Without the `_has_language` gate, `_dispatch`
+/// raises "unknown language: python" (caught by the after-load pcall and
+/// reported through `pmacs.error`), which we assert does NOT happen.
+#[test]
+fn m4_shebang_extensionless_grammarless_language_is_silent() {
+    use pmacs::editor::EditorState;
+    let s = EditorState::new();
+    let dir = tempfile::tempdir().expect("tempdir");
+    let f = dir.path().join("generate"); // no extension
+    std::fs::write(&f, b"#!/usr/bin/env python3\nprint('hi')\n").expect("write");
+    let f_disp = f.display();
+    s.lua_host
+        .lua()
+        .load(format!(
+            "pmacs.lsp.config = {{}}
+             _G.__errs = {{}}
+             local real = pmacs.error
+             pmacs.error = function(m) table.insert(_G.__errs, m) end
+             pmacs.buffer.find_or_open('{f_disp}')"
+        ))
+        .exec()
+        .expect("open extensionless python script");
+    let (lang, has_view, errs): (Option<String>, bool, i64) = s
+        .lua_host
+        .lua()
+        .load(
+            "return pmacs.lsp.active_buffer_language(),
+                    pmacs.parse._has_view(pmacs.window.buffer()),
+                    #_G.__errs",
+        )
+        .eval()
+        .expect("probe");
+    assert_eq!(lang.as_deref(), Some("python"), "python resolves for LSP");
+    assert!(
+        !has_view,
+        "no grammar parse view for a grammarless language"
+    );
+    assert_eq!(errs, 0, "no 'unknown language' error reported");
+}
+
+/// Finding-2 pin: editing an open extensionless script's shebang must not
+/// re-switch the parse grammar. A `#!/bin/sh` script attaches the bash
+/// grammar; rewriting its shebang to lua and firing after-edit must keep
+/// the bash tree (the pinned grammar) rather than swap in lua under the
+/// stale highlight overlay — and must not error.
+#[test]
+fn m4_shebang_edit_keeps_pinned_grammar() {
+    use pmacs::editor::EditorState;
+    let mut s = EditorState::new();
+    let dir = tempfile::tempdir().expect("tempdir");
+    let hook = dir.path().join("deploy"); // no extension
+    std::fs::write(&hook, b"#!/bin/sh\necho one\n").expect("write");
+    let hook_disp = hook.display();
+    s.lua_host
+        .lua()
+        .load(format!(
+            "pmacs.lsp.config = {{}}
+             _G.__errs = {{}}
+             local real = pmacs.error
+             pmacs.error = function(m) table.insert(_G.__errs, m) end
+             pmacs.buffer.find_or_open('{hook_disp}')"
+        ))
+        .exec()
+        .expect("open extensionless shell script");
+    pump_async(&mut s, |st| {
+        current_tree_language(st).as_deref() == Some("bash")
+    });
+
+    // Rewrite the first line to a lua shebang, then fire after-edit.
+    s.lua_host
+        .lua()
+        .load(
+            "local b = pmacs.window.buffer()
+             local text = b:slice(0, b:len())
+             local first_len = (text:find('\\n', 1, true) or 1) - 1
+             b:replace(0, first_len, '#!/usr/bin/env lua')
+             pmacs.hook.run('buffer.after-edit')",
+        )
+        .exec()
+        .expect("rewrite shebang to lua");
+    // Let the reparse settle (manual ticks: the tree stays bash with the
+    // pin, so a `pump_async` for a language *change* would time out).
+    for _ in 0..64 {
+        s.tick_async();
+        std::thread::sleep(Duration::from_millis(2));
+    }
+    assert_eq!(
+        current_tree_language(&s).as_deref(),
+        Some("bash"),
+        "editing the shebang must not re-switch the pinned grammar"
+    );
+    let errs: i64 = s
+        .lua_host
+        .lua()
+        .load("return #_G.__errs")
+        .eval()
+        .expect("errs");
+    assert_eq!(errs, 0, "reparse with the pinned grammar reports no error");
 }
 
 /// Typing-perf: the default bundle coalesces full-document