feat(parser): WASM VT500 scanner with ScanResult SOA dispatch

- Add C WASM scanner emitting structure-of-arrays ops (kinds, starts, lengths, aux, params)
- Integrate scan+dispatch in EscapeSequenceParser with async handler resume
- Fix CSI fast-path final byte index, ERROR state reporting, and precedingJoinState for REP
- Add build pipeline (build_parser_wasm.sh, transition table generator, wasm embed)

Co-authored-by: Daniel Imms <Tyriar@users.noreply.github.com>

bin/build_parser_wasm.sh

@@ -0,0 +1,45 @@
+#!/usr/bin/env bash
+# Copyright (c) 2026 The xterm.js authors. All rights reserved.
+# @license MIT
+set -euo pipefail
+ROOT="$(cd "$(dirname "$0")/.." && pwd)"
+cd "$ROOT"
+
+if [[ ! -f src/common/parser/wasm/transition_table.h ]]; then
+  npm run build
+  node bin/gen_parser_transition_table.mjs
+fi
+
+WASM_DIR=src/common/parser/wasm
+OUT="$WASM_DIR/parser.wasm"
+
+clang --target=wasm32-unknown-unknown -O2 -nostdlib -fuse-ld=lld \
+  -Wl,--no-entry \
+  -Wl,--export-memory \
+  -Wl,--export=reset \
+  -Wl,--export=scan \
+  -Wl,--export=probe_action \
+  -Wl,--export=set_state \
+  -Wl,--export=sync_params_from \
+  -Wl,--export=export_params_to \
+  -Wl,--export=get_params_len \
+  -Wl,--export=get_subparams_len \
+  -Wl,--export=get_subparams_ptr \
+  -Wl,--export=get_subparams_idx_ptr \
+  -Wl,--export=get_input_ptr \
+  -Wl,--export=get_kinds_ptr \
+  -Wl,--export=get_starts_ptr \
+  -Wl,--export=get_lengths_ptr \
+  -Wl,--export=get_aux_ptr \
+  -Wl,--export=get_param_starts_ptr \
+  -Wl,--export=get_param_counts_ptr \
+  -Wl,--export=get_params_ptr \
+  -Wl,--export=get_state_ptr \
+  -Wl,--export=get_header_ptr \
+  -Wl,--initial-memory=67108864 \
+  -Wl,--max-memory=67108864 \
+  "$WASM_DIR/parser.c" -o "$OUT"
+
+node bin/embed_parser_wasm.mjs
+
+echo "Built $OUT"

bin/embed_parser_wasm.mjs

@@ -0,0 +1,23 @@
+/**
+ * Copyright (c) 2026 The xterm.js authors. All rights reserved.
+ * @license MIT
+ */
+
+import { readFileSync, writeFileSync } from 'fs';
+import { join, dirname } from 'path';
+import { fileURLToPath } from 'url';
+
+const __dirname = dirname(fileURLToPath(import.meta.url));
+const root = join(__dirname, '..');
+const wasm = readFileSync(join(root, 'src/common/parser/wasm/parser.wasm'));
+const b64 = wasm.toString('base64');
+
+const out = `/**
+ * Copyright (c) 2026 The xterm.js authors. All rights reserved.
+ * @license MIT
+ */
+/** Base64-encoded parser.wasm (generated by bin/build_parser_wasm.sh) */
+export const PARSER_WASM_BASE64 = '${b64}';\n`;
+
+writeFileSync(join(root, 'src/common/parser/wasm/parser.wasm.embed.ts'), out);
+console.info(`Embedded parser.wasm (${wasm.length} bytes)`);

bin/gen_parser_transition_table.mjs

@@ -0,0 +1,34 @@
+/**
+ * Copyright (c) 2026 The xterm.js authors. All rights reserved.
+ * @license MIT
+ */
+
+// @ts-check
+import { writeFileSync } from 'fs';
+import { fileURLToPath } from 'url';
+import { dirname, join } from 'path';
+
+const __dirname = dirname(fileURLToPath(import.meta.url));
+const root = join(__dirname, '..');
+
+// Import compiled transition table
+const { VT500_TRANSITION_TABLE } = await import(join(root, 'out/common/parser/EscapeSequenceParser.js'));
+
+const table = VT500_TRANSITION_TABLE.table;
+let out = '/* Auto-generated by bin/gen_parser_transition_table.mjs - do not edit */\n';
+out += `#ifndef PARSER_TRANSITION_TABLE_H\n#define PARSER_TRANSITION_TABLE_H\n\n`;
+out += `#include <stdint.h>\n\n`;
+out += `#define PARSER_TABLE_SIZE ${table.length}\n\n`;
+out += `static const uint16_t PARSER_TRANSITION_TABLE[PARSER_TABLE_SIZE] = {\n`;
+for (let i = 0; i < table.length; i++) {
+  if (i % 16 === 0) out += '  ';
+  out += `0x${table[i].toString(16)}`;
+  out += i < table.length - 1 ? ', ' : '';
+  if (i % 16 === 15) out += '\n';
+}
+if (table.length % 16 !== 0) out += '\n';
+out += `};\n\n#endif\n`;
+
+const headerPath = join(root, 'src/common/parser/wasm/transition_table.h');
+writeFileSync(headerPath, out);
+console.info(`Wrote ${headerPath} (${table.length} entries)`);