feat(python-face): ADR-010 Priority 2 — Python-style surface syntax

Adds lib/python_face.ml: a source-level text transformer that maps
Python-style AffineScript to canonical AffineScript before lex+parse.
The compiler is entirely face-agnostic; only python_face.ml knows about
the transformation.

Supported surface mappings
  def → fn, True/False/None → true/false/()
  and/or/not → &&/||/!
  class → type, pass → ()
  # comment → // comment
  import a.b → use a::b, from a import b → use a::b
  INDENT/DEDENT → {}/} (indentation-based blocks)
  colon-at-EOL → { (block-opening)
  else:/elif COND: → else {/else if COND { (merged with dedent })
  statement lines get automatic ;

CLI: `affinescript parse --face python FILE`
     `affinescript preview-python FILE` (debug: show canonical text)

5 new E2E tests (Python-Face suite). 73/73 total: 0 regressions.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: hyperpolymath

.machine_readable/6a2/STATE.a2ml

@@ -9,10 +9,10 @@ status = "active"
 
 [project-context]
 name = "affinescript"
-completion-percentage = 80
-phase = "adr-009-conformance-complete"
+completion-percentage = 82
+phase = "python-face-complete"
 tagline = "Rust-inspired language with affine types, dependent types, row polymorphism, and extensible effects"
-note = "ADR-009 conformance target reached 2026-04-11: 12/12 valid conformance tests parse and match expected output (was 0/12). Six parser/lexer issues fixed: float scientific notation, optional type-decl semicolons, enum leading-pipe syntax, effect op type params, row variable support (type + expression contexts), keyword field names. 68/68 E2E tests: 0 regressions. Next: Priority 2 Faces Architecture (ASS / parser layer faces)."
+note = "Python-face (ADR-010 Priority 2) shipped 2026-04-11. lib/python_face.ml: source-level transformer mapping Python surface syntax to canonical AffineScript before lex+parse. Mappings: def→fn, True/False/None→true/false/(), and/or/not→&&/||/!, class→type, pass→(), #→//, import→use, INDENT/DEDENT→{}/}, colon-at-EOL block openers, else/elif chains. `--face python` flag on `parse` subcommand. 5 new Python-face E2E tests. 73/73 E2E tests: 0 regressions. Previous: ADR-009 conformance complete 2026-04-11 (12/12 valid conformance tests). Next: Priority 3 — LSP Phase B (completion, hover) or borrow checker Phase 3."
 
 [components]
 lexer = "complete-minus-affine-tokens (ZERO/ONE tokens for quantity literals NOT emitted; blocks QTT surface syntax). float_exponent now correctly named sub-regexp — scientific notation crash fixed 2026-04-11."
@@ -31,8 +31,8 @@ lsp-phase-d = "pending"
 stdlib = "95% (5 stubs remain as extern builtins)"
 
 [stats]
-compiler-loc = 12424
-compiler-modules = 38
+compiler-loc = 12712
+compiler-modules = 39
 lsp-files = 5
 test-files = 54
 

bin/main.ml

@@ -59,10 +59,21 @@ let lex_file path =
     Format.eprintf "@[<v>%s:%d:%d: error: %s@]@." path pos.line pos.col msg;
     `Error (false, "Lexer error")
 
+(** Preview the Python-face text transform (debug tool). *)
+let preview_python_transform path =
+  let ch = open_in_bin path in
+  let s = really_input_string ch (in_channel_length ch) in
+  close_in ch;
+  print_string (Affinescript.Python_face.preview_transform s);
+  `Ok ()
+
 (** Parse a file and print AST (no --json support). *)
-let parse_file path =
+let parse_file face path =
   try
-    let prog = Affinescript.Parse_driver.parse_file path in
+    let prog = match face with
+      | `Canonical -> Affinescript.Parse_driver.parse_file path
+      | `Python    -> Affinescript.Python_face.parse_file_python path
+    in
     Format.printf "%s@." (Affinescript.Ast.show_program prog);
     `Ok ()
   with
@@ -433,6 +444,16 @@ let wasm_gc_arg =
           Requires a runtime that supports the GC proposal: V8/Chrome ≥ 119, \
           SpiderMonkey/Firefox ≥ 120, or Wasmtime with --wasm-features gc.")
 
+(** Shared --face flag: select the parser surface-syntax face. *)
+let face_arg =
+  let faces = Arg.enum [("canonical", `Canonical); ("python", `Python)] in
+  Arg.(value & opt faces `Canonical & info ["face"]
+    ~docv:"FACE"
+    ~doc:"Parser face (surface-syntax variant). $(docv) must be $(b,canonical) \
+          (default, standard AffineScript) or $(b,python) (Python-style syntax: \
+          indentation-based blocks, $(b,def)/$(b,True)/$(b,False)/$(b,None)/\
+          $(b,and)/$(b,or)/$(b,not) etc. — compiled to the same canonical AST).")
+
 let lex_cmd =
   let doc = "Lex a file and print tokens" in
   let info = Cmd.info "lex" ~doc in
@@ -441,7 +462,7 @@ let lex_cmd =
 let parse_cmd =
   let doc = "Parse a file and print AST" in
   let info = Cmd.info "parse" ~doc in
-  Cmd.v info Term.(ret (const parse_file $ path_arg))
+  Cmd.v info Term.(ret (const parse_file $ face_arg $ path_arg))
 
 let check_cmd =
   let doc = "Type check a file" in
@@ -473,10 +494,15 @@ let lint_cmd =
   let info = Cmd.info "lint" ~doc in
   Cmd.v info Term.(ret (const lint_file $ json_arg $ path_arg))
 
+let preview_python_cmd =
+  let doc = "Preview the Python-face text transform (debug)" in
+  let info = Cmd.info "preview-python" ~doc in
+  Cmd.v info Term.(ret (const preview_python_transform $ path_arg))
+
 let default_cmd =
   let doc = "The AffineScript compiler" in
   let info = Cmd.info "affinescript" ~version ~doc in
   let default = Term.(ret (const (`Help (`Pager, None)))) in
-  Cmd.group info ~default [lex_cmd; parse_cmd; check_cmd; eval_cmd; repl_cmd; compile_cmd; fmt_cmd; lint_cmd]
+  Cmd.group info ~default [lex_cmd; parse_cmd; check_cmd; eval_cmd; repl_cmd; compile_cmd; fmt_cmd; lint_cmd; preview_python_cmd]
 
 let () = exit (Cmd.eval default_cmd)

lib/dune

@@ -2,7 +2,7 @@
  (name affinescript)
  (public_name affinescript)
  (modes byte native)
- (modules ast codegen codegen_gc desugar_traits effect error error_collector error_formatter formatter interp julia_codegen json_output lexer linter module_loader opt parse_driver parse parser parser_errors quantity resolve span symbol token trait typecheck types unify value wasm wasm_encode wasm_gc wasm_gc_encode wasi_runtime)
+ (modules ast codegen codegen_gc desugar_traits effect error error_collector error_formatter formatter interp julia_codegen json_output lexer linter module_loader opt parse_driver parse parser parser_errors python_face quantity resolve span symbol token trait typecheck types unify value wasm wasm_encode wasm_gc wasm_gc_encode wasi_runtime)
  (libraries str unix sedlex fmt menhirLib yojson)
  (preprocess
   (pps ppx_deriving.show ppx_deriving.eq ppx_deriving.ord sedlex.ppx)))