feat(vscode): function-value callback ABI — registerCommand/onDidSave/withProgress (Refs #199)

#199 PR-5a (owner chose the function-value ABI). Replaces the brittle
wasm-table-index `handler: Int` convention with real function values.

ABI shape: `handler: fn(Unit) -> R` (not `fn() -> R`). AffineScript
types a zero-param function as its bare return type (typecheck.ml:752),
so `fn() -> Int` collapses to `Int`; the explicit `Unit` param is the
honest callback shape and needs zero compiler change (verified).

- stdlib/Vscode.affine: registerCommand / onDidSaveTextDocument /
  withProgressNotification handler params Int -> fn(Unit) -> R. Also
  removes the duplicate `extern type Thenable;` introduced in #198
  (line 43 already declares it) — resolved at source.
- examples/vscode_extension_minimal.affine + editors/vscode/src/
  extension.affine: call sites migrated from numbered indices to
  `fn(u: Unit) => handler_x()` lambdas (behaviour-preserving; named
  handlers unchanged).

Verified: stdlib/example/editors all typecheck; dune test 253/253
(the prior Examples-parse regression was my own `_u` typo — leading-
underscore idents parse-error in params, a separate minor lexer
observation; used `u`). Deno-ESM emits
`registerCommand("…", ((u) => handler_0()))` — a real JS arrow passed
directly, so the Deno fn-value extern path (PR-5b) needs no codegen
change. Wasm/mod.js marshalling (PR-5c) and the rsr-certifier pilot
(PR-5d) follow.

Refs #199

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: hyperpolymath

editors/vscode/src/extension.affine

@@ -142,15 +142,15 @@ fn start_lsp() -> Int {
 pub fn activate(ctx: ExtensionContext) -> Int {
   let _ = consoleLog("AffineScript extension activated");
 
-  // Register commands. The integer second argument to registerCommand is
-  // the wasm-table index of the handler — populated by the JS-side adapter
-  // from the `__indirect_function_table` export. The order here must
-  // match the order handlers appear in the file.
-  let _ = pushSubscription(ctx, registerCommand("affinescript.check", 0));
-  let _ = pushSubscription(ctx, registerCommand("affinescript.eval", 1));
-  let _ = pushSubscription(ctx, registerCommand("affinescript.compile", 2));
-  let _ = pushSubscription(ctx, registerCommand("affinescript.format", 3));
-  let _ = pushSubscription(ctx, registerCommand("affinescript.restartLsp", 4));
+  // Register commands. The handler is now a function value (#199
+  // function-value callback ABI) — no more brittle wasm-table indices.
+  // Each lambda takes the explicit `Unit` param (zero-param-fn return-
+  // type collapse) and delegates to the named handler.
+  let _ = pushSubscription(ctx, registerCommand("affinescript.check", fn(u: Unit) => handler_check()));
+  let _ = pushSubscription(ctx, registerCommand("affinescript.eval", fn(u: Unit) => handler_eval()));
+  let _ = pushSubscription(ctx, registerCommand("affinescript.compile", fn(u: Unit) => handler_compile()));
+  let _ = pushSubscription(ctx, registerCommand("affinescript.format", fn(u: Unit) => handler_format()));
+  let _ = pushSubscription(ctx, registerCommand("affinescript.restartLsp", fn(u: Unit) => handler_restart_lsp()));
 
   let cfg = getConfiguration("affinescript");
   if workspaceConfigGetBool(cfg, "lsp.enabled", 1) != 0 {

examples/vscode_extension_minimal.affine

@@ -23,7 +23,7 @@ pub fn handler_0() -> Int {
 }
 
 pub fn activate(ctx: ExtensionContext) -> Int {
-  let d = registerCommand("affinescript.helloAffine", 0);  // 0 = handler table index
+  let d = registerCommand("affinescript.helloAffine", fn(u: Unit) => handler_0());
   let _ = pushSubscription(ctx, d);
   return 0;
 }

stdlib/Vscode.affine

@@ -51,9 +51,11 @@ pub extern type TextDocument;
 // ── vscode.commands ───────────────────────────────────────────────────
 
 /// `vscode.commands.registerCommand(name, handler)`.
-/// `handler` is a function-pointer index into the Wasm table; the JS shim
-/// wraps it as a JS callback that re-enters Wasm when invoked.
-pub extern fn registerCommand(name: String, handler: Int) -> Disposable;
+/// `handler` is a function value (#199 function-value callback ABI). The
+/// `Unit` parameter is explicit because AffineScript types a zero-param
+/// function as its bare return type — `fn() -> Int` would collapse to
+/// `Int`; `fn(Unit) -> Int` is the honest callback shape.
+pub extern fn registerCommand(name: String, handler: fn(Unit) -> Int) -> Disposable;
 
 // ── vscode.workspace ──────────────────────────────────────────────────
 
@@ -263,7 +265,7 @@ pub extern fn clipboardWriteText(text: String) -> Int;
 /// `editorActiveFilePath()` from inside the thunk. That covers the
 /// 95% case where the saved doc is the active editor; the remaining
 /// cases (background-saved docs) degrade to "no action".
-pub extern fn onDidSaveTextDocument(handler: Int) -> Disposable;
+pub extern fn onDidSaveTextDocument(handler: fn(Unit) -> Int) -> Disposable;
 
 // ── Path helpers ─────────────────────────────────────────────────────
 
@@ -295,10 +297,11 @@ pub extern fn extensionAbsolutePath(ctx: ExtensionContext, rel_path: String) ->
 // JS implementation lives in packages/affine-vscode/mod.js (follow-up
 // slice); these declarations are the binding surface + effect tracking.
 
-pub extern type Thenable;
+// `Thenable` is already declared in the opaque-type block above; no
+// re-declaration here (the duplicate from #198 is removed at source).
 
 /// `vscode.window.withProgress({ location: Notification, title }, task)`.
-/// `work_thunk` is a wasm/host table index of the `() -> Thenable` task
-/// (same thunk-handle convention as `onDidSaveTextDocument`). Returns the
-/// progress Thenable.
-pub extern fn withProgressNotification(title: String, work_thunk: Int) -> Thenable / Async;
+/// `work` is the task function (#199 function-value callback ABI; the
+/// explicit `Unit` param avoids the zero-param-fn return-type collapse).
+/// Returns the progress Thenable.
+pub extern fn withProgressNotification(title: String, work: fn(Unit) -> Thenable) -> Thenable / Async;