fix(forge): autocompletion Tab naturelle et fiable (BUG-055)

frontend/js/autocomplete.js

@@ -347,4 +347,97 @@ function filterFiles(partial) {
   });
 }
 
-export { suggest, searchWikilinks, detectContext, MERMAID_TYPES, CODE_LANGUAGES, FRONTMATTER_FIELDS, MARKDOWN_FORMAT };
+// ── Word completion (Forge « Tab » completion) ────────────────────────
+// A word character matches the same set used by the editor: letters, digits,
+// underscore, dash, dot and slash (so paths like `docs/guide` complete too).
+var _WORD_CHAR = /[\w\-.\/]/;
+
+function isWordChar(ch) {
+  return !!ch && _WORD_CHAR.test(ch);
+}
+
+/** Return the word fragment immediately before the cursor. */
+function getWordFragment(text, cursorPos) {
+  var start = cursorPos;
+  while (start > 0 && isWordChar(text.charAt(start - 1))) start--;
+  return { start: start, fragment: text.slice(start, cursorPos) };
+}
+
+/**
+ * Collect unique words of `text` that start with `fragment` (case-insensitive).
+ * The occurrence currently being typed at the cursor is ignored. `limit` caps
+ * the number of candidates (0 = no limit).
+ */
+function findWordCompletions(text, cursorPos, fragment, limit) {
+  if (!fragment || fragment.length < 2) return [];
+  var lower = fragment.toLowerCase();
+  var re = /[\w\-.\/]+/g;
+  var seen = Object.create(null);
+  var out = [];
+  var m;
+  while ((m = re.exec(text)) !== null) {
+    var word = m[0];
+    if (word.length <= fragment.length) continue;
+    if (word.toLowerCase().indexOf(lower) !== 0) continue;
+    // Skip the word currently being typed (it starts exactly at the cursor).
+    if (m.index === cursorPos - fragment.length) continue;
+    var key = word.toLowerCase();
+    if (seen[key]) continue;
+    seen[key] = true;
+    out.push(word);
+    if (limit && out.length >= limit) break;
+  }
+  return out;
+}
+
+/**
+ * Clean up a raw AI prediction before displaying/inserting it.
+ *
+ * - strips the echoed input prefix (mid-word or full context),
+ * - for a mid-word completion, keeps only the first token so a word completion
+ *   can never introduce a stray space,
+ * - trims any remaining leading whitespace.
+ */
+function normalizeGhost(raw, inputText, midWord) {
+  var p = raw == null ? '' : String(raw).trim();
+  if (!p) return '';
+  if (inputText) {
+    var inp = String(inputText);
+    if (midWord && p.toLowerCase().indexOf(inp.toLowerCase()) === 0) {
+      p = p.slice(inp.length);
+    } else if (!midWord && p.indexOf(inp) === 0) {
+      p = p.slice(inp.length);
+    }
+  }
+  if (midWord) p = p.split(/\s+/)[0];
+  return p.replace(/^\s+/, '');
+}
+
+/**
+ * Decide what the « Tab » key should do. Kept pure so the editor and the tests
+ * share the exact same priority rules.
+ *
+ *   dropdown  → an autocomplete list is open: accept the highlighted item
+ *   ghost     → an AI inline prediction is displayed: accept it
+ *   dedent    → Shift+Tab: remove indentation
+ *   word      → a single document word matches: insert its suffix
+ *   word-list → several words match: open the suggestion list
+ *   indent    → default: indent the current line
+ */
+function chooseTabAction(state) {
+  state = state || {};
+  if (state.dropdownOpen) return 'dropdown';
+  if (state.ghost) return 'ghost';
+  if (state.shiftKey) return 'dedent';
+  if (state.hasSelection) return 'indent';
+  var candidates = state.candidates || [];
+  if (candidates.length === 1) return 'word';
+  if (candidates.length > 1) return 'word-list';
+  return 'indent';
+}
+
+export {
+  suggest, searchWikilinks, detectContext,
+  MERMAID_TYPES, CODE_LANGUAGES, FRONTMATTER_FIELDS, MARKDOWN_FORMAT,
+  isWordChar, getWordFragment, findWordCompletions, normalizeGhost, chooseTabAction,
+};