fix(wasm-canvas): stop duplicate wasm_push_key; tune statement yields

wasm_push_key no longer pushes to wasm_key_ring when gfx_vs is set;
GET consumed queue then ring, doubling keys (skipped RETURN waits).

Relax execute_statement (128) and run_program (32) yields so pause/resume
test passes; MID$/LEFT$/RIGHT$ yields unchanged.

Add examples/wasm_canvas_hang_probe.bas for isolated hang/GET checks.

Author: cursoragent

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ### Unreleased
 
+- **WASM canvas yields**: **`execute_statement`** / **`run_program`** yield intervals relaxed (**128** / **32** statements) so **pause → resume** keeps advancing tight **`FOR`** loops in tests; **string-builtin** yields still cover **`trek.bas`**-style **`MID$`** storms.
+
+- **Canvas `wasm_push_key` duplicate keys**: **`wasm_push_key`** was enqueueing every byte into **both** the **GFX key queue** and **`wasm_key_ring`**. **`GET`** consumed the queue first, then **`read_single_char_nonblock`** read the **same** byte again from the ring → **double keypresses** and **skipped “press RETURN”** waits in **`trek.bas`**. **Canvas GFX** now pushes **only** to the **GFX queue** (ring used when **`gfx_vs`** is unset).
+
 - **WASM canvas trek / string builtins**: **`trek.bas`** SRS **`PRINT`** evaluates **`MID$` / `LEFT$` / `RIGHT$`** hundreds of times **inside one** **`PRINT`** (few **`gfx_put_byte`** calls until the line ends). **Canvas WASM** now yields every **64** **`MID$`/`LEFT$`/`RIGHT$`** completions, plus periodic yields in **`INSTR`** / **`REPLACE`** scans and **`STRING$`** expansion.
 
 - **WASM canvas trek / compound lines**: **`wasm_stmt_budget`** in **`run_program`** advances once per **`execute_statement` chain** from a source line, but **`trek.bas`** can run **hundreds** of **`:`**-separated statements (**`LET`**, **`IF`**, **`GOTO`**) without **`PRINT`** → no **`gfx_put_byte`** yield → tab **unresponsive**. **`execute_statement`** now yields every **4** statements (**pause**, **`wasm_gfx_refresh_js`**, **`emscripten_sleep(0)`**) when **`__EMSCRIPTEN__` + `GFX_VIDEO`**.

basic.c

@@ -1353,7 +1353,8 @@ static void wasm_canvas_sync_charset_from_options(void);
 EMSCRIPTEN_KEEPALIVE void wasm_push_key(unsigned int code)
 {
     unsigned char b = (unsigned char)(code & 0xFF);
-    wasm_key_push_byte(b);
+    /* Canvas: GET uses gfx key queue only. Pushing to wasm_key_ring too would
+     * deliver the same key twice (queue first, then ring in read_single_char_nonblock). */
     if (gfx_vs) {
         uint8_t next = (uint8_t)(gfx_vs->key_q_tail + 1);
         if (next >= (uint8_t)sizeof(gfx_vs->key_queue)) {
@@ -1363,6 +1364,8 @@ EMSCRIPTEN_KEEPALIVE void wasm_push_key(unsigned int code)
             gfx_vs->key_queue[gfx_vs->key_q_tail] = b;
             gfx_vs->key_q_tail = next;
         }
+    } else {
+        wasm_key_push_byte(b);
     }
 }
 #endif
@@ -8043,7 +8046,8 @@ static void execute_statement(char **p)
     }
 #if defined(__EMSCRIPTEN__) && defined(GFX_VIDEO)
     wasm_gfx_stmt_exec_budget++;
-    if ((wasm_gfx_stmt_exec_budget & 3u) == 0u) {
+    /* Rare: tight FOR/NEXT (pause/resume test) must advance POKE every few ms when unpaused. */
+    if ((wasm_gfx_stmt_exec_budget & 127u) == 0u) {
         wasm_browser_pause_point();
         if (!halted) {
             wasm_gfx_refresh_js();
@@ -9006,8 +9010,8 @@ static void run_program(const char *script_path_arg, int nargs, char **args)
 #if defined(__EMSCRIPTEN__)
         wasm_stmt_budget++;
 #if defined(GFX_VIDEO)
-        /* Compound lines (trek.bas) run many statements before next line; yield often. */
-        if ((wasm_stmt_budget & 7) == 0) {
+        /* Compound lines (trek.bas): yield without slowing tight FOR/NEXT too much. */
+        if ((wasm_stmt_budget & 31) == 0) {
             wasm_browser_pause_point();
             if (halted) {
                 break;

examples/wasm_canvas_hang_probe.bas

@@ -0,0 +1,40 @@
+REM --- Paste into canvas.html; click canvas before GET tests ---
+REM --- Use Stop if a phase hangs; note which phase in bug reports ---
+
+REM Phase A: GET echo (one key per line; should NOT skip prompts)
+REM 10 PRINT "PHASE A: type 3 keys (e.g. a b c), each should print once"
+REM 20 GET K$
+REM 30 IF K$="" THEN 20
+REM 40 PRINT K$
+REM 50 GOTO 20
+
+REM Phase B: MID$ storm (similar workload to trek SRS inner loop)
+10 PRINT "PHASE B: MID$ x2000 — should finish without freezing"
+20 Q$=STRING$(200,"x")
+30 FOR I=1 TO 2000
+40 A$=MID$(Q$,1,1)
+50 NEXT I
+60 PRINT "OK B"
+70 END
+
+REM Phase C: STRING$ + PRINT (gfx_put_byte yields)
+REM 10 PRINT "PHASE C: long PRINT"
+REM 20 PRINT STRING$(3000,".")
+REM 30 PRINT "OK C"
+REM 40 END
+
+REM Phase D: tight FOR no PRINT (statement-level yields only)
+REM 10 PRINT "PHASE D: FOR 2M POKE only"
+REM 20 FOR I=1 TO 2000000
+REM 30 POKE 1024,(I AND 255)
+REM 40 NEXT I
+REM 50 PRINT "OK D"
+REM 60 END
+
+REM Phase E: trek-style GET loop (press RETURN to exit)
+REM 10 PRINT "PHASE E: press RETURN once to continue"
+REM 20 GET K$
+REM 30 IF K$="" THEN 20
+REM 40 IF ASC(K$)<>13 THEN 20
+REM 50 PRINT "OK E"
+REM 60 END