feat: multi-turn conversation support (0.4.0)

anonymizeTurn(text, session) threads a serializable AnonymizerSession
({mapping, legend, history}) so one entity keeps one id across a whole chat
(applyKnown reuse + usedIds + de-collision merge). Adds conversation()
in-memory wrapper and an optional LlmProvider.anonymizeInConversation(text, ctx)
for rich cross-turn context; providers without it fall back to the batch path.

openAICompatibleProvider gains includeMappingInContext (default false — only
send real values to a trusted anonymizer endpoint) + historyMaxTurns (default
10). Verified live vs Gemma 4: Nora stays PER_1 across 4 turns (name/email/AVS/
IBAN), Yanis = PER_2; 41 tests, 98% coverage.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/providers/openai-compatible.ts

@@ -64,6 +64,15 @@ export interface OpenAICompatibleOptions {
    * responses are parsed leniently (markdown fences / surrounding prose tolerated).
    */
   responseFormat?: Record<string, unknown>;
+  /**
+   * Include the secret `mapping` (placeholder → real value) in the conversation
+   * context during {@link LlmProvider.anonymizeInConversation}. **Default false.**
+   * Enable ONLY when this endpoint is a trusted processor — it sends REAL values
+   * to the model. (The anonymizer already receives the cleartext being
+   * anonymized, so a trusted endpoint like a Swiss/self-hosted deployment sees no
+   * more than it already does; the downstream chatbot never receives the mapping.)
+   */
+  includeMappingInContext?: boolean;
   /** Override the system prompt (e.g. for another language or regulation). */
   systemPrompt?: string;
   /** Extra instructions appended to the system prompt in batch mode. */
@@ -115,6 +124,42 @@ const DEFAULT_BATCH_INSTRUCTIONS = (usedIds: string[]): string =>
   '\n- SORTIE STRICTEMENT JSON : {"segments": ["…anonymisé…"], "mapping": {"[PER_1.NOM:M]": "…"}, "legende": {"PER": "Personne"}}.' +
   '\n- "segments" DOIT avoir la même longueur et le même ordre que l’entrée ; "mapping" ne contient que les NOUVELLES entités ; "legende" décrit toutes les abréviations utilisées.';
 
+/** Prior-conversation context block appended to the system prompt for a turn. */
+function conversationContext(
+  ctx: {
+    history: string[];
+    legend: Record<string, string>;
+    usedIds: string[];
+    mapping?: Record<string, string>;
+  },
+  includeMapping: boolean,
+): string {
+  const lines = ['', 'CONTEXTE DE LA CONVERSATION (déjà pseudonymisé) :'];
+  if (ctx.history.length) {
+    lines.push('- Tours précédents :', ...ctx.history.map((h, i) => `  [${i + 1}] ${h}`));
+  }
+  if (Object.keys(ctx.legend).length) {
+    lines.push(`- Légende connue : ${JSON.stringify(ctx.legend)}`);
+  }
+  if (ctx.usedIds.length) {
+    lines.push(
+      `- Identifiants DÉJÀ attribués (réutilise-les pour les MÊMES entités, n'en réattribue AUCUN à une autre valeur) : ${ctx.usedIds.join(', ')}`,
+    );
+  }
+  if (includeMapping && ctx.mapping && Object.keys(ctx.mapping).length) {
+    const pairs = Object.entries(ctx.mapping)
+      .map(([ph, v]) => `${ph} = ${v}`)
+      .join(' ; ');
+    lines.push(
+      `- Correspondances connues (réutilise le MÊME placeholder si la valeur réapparaît) : ${pairs}`,
+    );
+  }
+  lines.push(
+    'Anonymise le MESSAGE suivant en gardant EXACTEMENT la même convention et les mêmes identifiants pour les entités déjà vues ; "mapping" ne contient que les NOUVELLES entités.',
+  );
+  return '\n\n' + lines.join('\n');
+}
+
 /**
  * Build an {@link LlmProvider} backed by any OpenAI-compatible Chat Completions
  * endpoint (OpenAI, Infomaniak, vLLM, Ollama, …). Uses `temperature: 0` for
@@ -128,6 +173,7 @@ export function openAICompatibleProvider(opts: OpenAICompatibleOptions): LlmProv
   const retries = Math.max(0, opts.retries ?? 1);
   const retryDelayMs = opts.retryDelayMs ?? 250;
   const responseFormat = opts.responseFormat;
+  const includeMappingInContext = opts.includeMappingInContext ?? false;
   const systemPrompt = opts.systemPrompt ?? DEFAULT_SYSTEM_PROMPT;
   const batchInstructions = opts.batchInstructions ?? DEFAULT_BATCH_INSTRUCTIONS;
 
@@ -206,6 +252,24 @@ export function openAICompatibleProvider(opts: OpenAICompatibleOptions): LlmProv
       return { anon: parsed.texte_anonymise, mapping: parsed.mapping, legend: asLegend(parsed.legende) };
     },
 
+    async anonymizeInConversation(text, ctx): Promise<AnonymizationResult> {
+      const system = systemPrompt + conversationContext(ctx, includeMappingInContext);
+      const content = await chat(system, text);
+      const parsed = extractJson(content) as {
+        texte_anonymise?: string;
+        mapping?: Record<string, string>;
+        legende?: Record<string, string>;
+      };
+      if (
+        typeof parsed.texte_anonymise !== 'string' ||
+        typeof parsed.mapping !== 'object' ||
+        !parsed.mapping
+      ) {
+        throw new Error('LLM_BAD_SHAPE');
+      }
+      return { anon: parsed.texte_anonymise, mapping: parsed.mapping, legend: asLegend(parsed.legende) };
+    },
+
     async anonymizeBatch(
       texts: string[],
       usedIds: string[],