feat(worktrees): démarrer une session sur la branche principale ou tout worktree

Ajoute le choix « créer un worktree OU bosser sur la branche principale » au
moment de démarrer le travail, sur deux surfaces :
- bouton « Démarrer » (claude/bash) sur chaque WorktreeCard, y compris le
  checkout principal (badge « principal ») — comblait un manque : impossible
  jusqu'ici de lancer une session sur un worktree existant depuis le dashboard ;
- toggle de mode (Worktree / Branche principale) dans le formulaire d'entête
  de RepoSection.

Option git « créer & basculer » : nouvel endpoint POST /api/v1/repos/:id/session
qui lance UNE session dans le checkout principal (repo.path), avec création ou
bascule de branche optionnelle (git switch[-c]) — refusée en 409 si l'arbre est
sale. Pas de hooks ni de pré-trust (c'est le dépôt réel de l'utilisateur).

- shared : type additif StartRepoSessionRequest.
- server : git.switchBranch + WorktreeManager.startMainSession + route.
- web : store worktrees.startMainSession, UI WorktreeCard/RepoSection, i18n fr/en.
- tests : +5 unitaires (switchBranch, startMainSession) ; acceptance-p3 étendue.

packages/web/src/components/RepoSection.vue

@@ -5,7 +5,7 @@
       <BaseBadge v-if="!repo.valid" tone="red">{{ t('repos.invalid') }}</BaseBadge>
       <span class="truncate font-mono text-xs text-zinc-500" :title="repo.path">{{ repo.path }}</span>
       <div class="ml-auto flex items-center gap-2">
-        <BaseButton size="sm" :icon="Plus" @click="creating = !creating">{{ t('worktrees.new') }}</BaseButton>
+        <BaseButton size="sm" :icon="Plus" @click="creating = !creating">{{ t('worktrees.startWork') }}</BaseButton>
         <BaseButton size="sm" :icon="Scissors" :loading="busy" @click="onPrune">{{ t('worktrees.prune') }}</BaseButton>
         <BaseButton
           size="sm"
@@ -18,23 +18,58 @@
       </div>
     </header>
 
-    <form v-if="creating" class="card-inset flex flex-wrap items-end gap-2" @submit.prevent="onCreate">
-      <label class="flex flex-1 flex-col gap-1 text-xs text-zinc-400">
-        {{ t('worktrees.branch') }}
-        <input v-model="branch" class="input font-mono" placeholder="feature/…" required />
-      </label>
-      <label class="flex flex-col gap-1 text-xs text-zinc-400">
-        {{ t('worktrees.start') }}
-        <select v-model="startSession" class="input">
-          <option :value="null">{{ t('worktrees.startNone') }}</option>
-          <option value="claude">claude</option>
-          <option value="bash">bash</option>
-        </select>
-      </label>
-      <label class="flex items-center gap-1 text-xs text-zinc-400"><input v-model="newBranch" type="checkbox" /> {{ t('worktrees.newBranch') }}</label>
-      <BaseButton type="submit" variant="primary" size="sm" :loading="busy" :disabled="branch.trim() === ''">
-        {{ t('worktrees.create') }}
-      </BaseButton>
+    <form v-if="creating" class="card-inset flex flex-col gap-2" @submit.prevent="onCreate">
+      <!-- mode : créer un worktree dédié, ou bosser directement sur le checkout principal -->
+      <div class="flex flex-wrap items-center gap-3 text-xs text-zinc-400">
+        {{ t('worktrees.modeLabel') }}
+        <label class="flex items-center gap-1.5"><input v-model="mode" type="radio" value="worktree" /> {{ t('worktrees.modeWorktree') }}</label>
+        <label class="flex items-center gap-1.5"><input v-model="mode" type="radio" value="main" /> {{ t('worktrees.modeMain') }}</label>
+      </div>
+
+      <div class="flex flex-wrap items-end gap-2">
+        <!-- mode worktree : branche + créer/existante -->
+        <template v-if="mode === 'worktree'">
+          <label class="flex flex-1 flex-col gap-1 text-xs text-zinc-400">
+            {{ t('worktrees.branch') }}
+            <input v-model="branch" class="input font-mono" placeholder="feature/…" required />
+          </label>
+          <label class="flex flex-col gap-1 text-xs text-zinc-400">
+            {{ t('worktrees.start') }}
+            <select v-model="startSession" class="input">
+              <option :value="null">{{ t('worktrees.startNone') }}</option>
+              <option value="claude">claude</option>
+              <option value="bash">bash</option>
+            </select>
+          </label>
+          <label class="flex items-center gap-1 text-xs text-zinc-400"><input v-model="newBranch" type="checkbox" /> {{ t('worktrees.newBranch') }}</label>
+        </template>
+
+        <!-- mode branche principale : option git (branche actuelle ou nouvelle branche) + commande -->
+        <template v-else>
+          <label class="flex flex-col gap-1 text-xs text-zinc-400">
+            {{ t('worktrees.branchModeLabel') }}
+            <select v-model="mainBranchMode" class="input">
+              <option value="current">{{ t('worktrees.currentBranch') }}</option>
+              <option value="new">{{ t('worktrees.newBranchOpt') }}</option>
+            </select>
+          </label>
+          <label v-if="mainBranchMode === 'new'" class="flex flex-1 flex-col gap-1 text-xs text-zinc-400">
+            {{ t('worktrees.branch') }}
+            <input v-model="branch" class="input font-mono" placeholder="feature/…" />
+          </label>
+          <label class="flex flex-col gap-1 text-xs text-zinc-400">
+            {{ t('worktrees.commandLabel') }}
+            <select v-model="mainCommand" class="input">
+              <option value="claude">claude</option>
+              <option value="bash">bash</option>
+            </select>
+          </label>
+        </template>
+
+        <BaseButton type="submit" variant="primary" size="sm" :loading="busy" :disabled="!canSubmit">
+          {{ mode === 'worktree' ? t('worktrees.create') : t('worktrees.start') }}
+        </BaseButton>
+      </div>
     </form>
     <p v-if="error" class="text-sm text-red-400">{{ error }}</p>
 
@@ -66,20 +101,37 @@ const toasts = useToastsStore();
 // applique le tri/filtre/recherche partagé (toolbar du dashboard) aux worktrees de ce repo.
 const worktrees = computed(() => view.apply(store.worktreesForRepo(props.repo.id)));
 const creating = ref(false);
+const mode = ref<'worktree' | 'main'>('worktree');
 const branch = ref('');
 const newBranch = ref(true);
 const startSession = ref<'claude' | 'bash' | null>(null);
+const mainBranchMode = ref<'current' | 'new'>('current');
+const mainCommand = ref<'claude' | 'bash'>('claude');
 const busy = ref(false);
 const error = ref<string | null>(null);
 
+// worktree : branche obligatoire ; branche principale + nouvelle branche : branche obligatoire ; sinon OK.
+const canSubmit = computed(() =>
+  mode.value === 'worktree' ? branch.value.trim() !== '' : mainBranchMode.value === 'current' || branch.value.trim() !== '',
+);
+
 async function onCreate(): Promise<void> {
   busy.value = true;
   error.value = null;
   try {
-    await store.createWorktree(props.repo.id, { branch: branch.value.trim(), newBranch: newBranch.value, startSession: startSession.value });
+    if (mode.value === 'worktree') {
+      await store.createWorktree(props.repo.id, { branch: branch.value.trim(), newBranch: newBranch.value, startSession: startSession.value });
+      toasts.success(t('toast.worktreeCreated'));
+    } else {
+      // bosser sur la branche principale : session dans le checkout principal, avec création de branche optionnelle.
+      await store.startMainSession(props.repo.id, {
+        command: mainCommand.value,
+        ...(mainBranchMode.value === 'new' ? { branch: branch.value.trim(), newBranch: true } : {}),
+      });
+      toasts.success(t('toast.sessionCreated'));
+    }
     branch.value = '';
     creating.value = false;
-    toasts.success(t('toast.worktreeCreated'));
   } catch (err) {
     error.value = err instanceof Error ? err.message : String(err);
   } finally {

packages/web/src/components/WorktreeCard.vue

@@ -26,6 +26,30 @@
       </RouterLink>
       <span v-if="worktree.sessions.length === 0" class="text-xs text-zinc-600">{{ t('worktrees.noSession') }}</span>
 
+      <!-- lancement d'une session sur ce worktree ; carte principale = bosser sur la branche principale -->
+      <button v-if="hasLiveSession && !showLauncher" class="btn text-xs" @click="showLauncher = true">+ {{ t('worktrees.start') }}</button>
+      <form v-if="!hasLiveSession || showLauncher" class="flex flex-wrap items-center gap-1" @submit.prevent="onStart">
+        <template v-if="worktree.isMain">
+          <select v-model="branchMode" class="input text-xs" :aria-label="t('worktrees.branchModeLabel')">
+            <option value="current">{{ t('worktrees.currentBranch') }}</option>
+            <option value="new">{{ t('worktrees.newBranchOpt') }}</option>
+          </select>
+          <input v-if="branchMode === 'new'" v-model="newBranchName" class="input w-32 font-mono text-xs" placeholder="feature/…" />
+        </template>
+        <select v-model="startCommand" class="input text-xs" :aria-label="t('worktrees.commandLabel')">
+          <option value="claude">claude</option>
+          <option value="bash">bash</option>
+        </select>
+        <button
+          type="submit"
+          class="btn-primary text-xs"
+          :disabled="starting || (worktree.isMain && branchMode === 'new' && newBranchName.trim() === '')"
+        >
+          {{ starting ? t('worktrees.starting') : t('worktrees.start') }}
+        </button>
+      </form>
+      <span v-if="startError" class="text-xs text-amber-400">{{ startError }}</span>
+
       <div v-if="!worktree.isMain" class="ml-auto flex items-center gap-2">
         <template v-if="confirming">
           <span v-if="error" class="text-xs text-amber-400">{{ error }}</span>
@@ -74,6 +98,39 @@ const forceNeeded = ref(false);
 const error = ref<string | null>(null);
 const busy = ref(false);
 
+// --- lancement de session sur ce worktree ---
+const hasLiveSession = computed(() => props.worktree.sessions.some((s) => liveSession(s).live));
+const showLauncher = ref(false);
+const startCommand = ref<'claude' | 'bash'>('claude');
+const branchMode = ref<'current' | 'new'>('current'); // carte principale uniquement
+const newBranchName = ref('');
+const starting = ref(false);
+const startError = ref<string | null>(null);
+
+async function onStart(): Promise<void> {
+  if (starting.value) return;
+  starting.value = true;
+  startError.value = null;
+  try {
+    if (props.worktree.isMain && branchMode.value === 'new') {
+      // bosser sur la branche principale en créant d'abord une branche dans le checkout principal.
+      await store.startMainSession(props.worktree.repoId, { command: startCommand.value, branch: newBranchName.value.trim(), newBranch: true });
+    } else {
+      // worktree existant (ou branche principale actuelle) : session directe dans son cwd.
+      await sessions.createSession(props.worktree.path, startCommand.value);
+    }
+    // resynchronise les worktrees du repo pour que la nouvelle session apparaisse sur la carte.
+    await store.refreshRepoWorktrees(props.worktree.repoId);
+    showLauncher.value = false;
+    newBranchName.value = '';
+    branchMode.value = 'current';
+  } catch (err) {
+    startError.value = err instanceof Error ? err.message : String(err);
+  } finally {
+    starting.value = false;
+  }
+}
+
 const branchLabel = computed(() =>
   props.worktree.branch ?? (props.worktree.detached ? `${t('worktrees.detached')} ${props.worktree.head.slice(0, 7)}` : '—'),
 );

packages/web/src/i18n/en.ts

@@ -141,7 +141,16 @@ export default {
     branch: 'Branch',
     newBranch: 'create branch',
     start: 'Start',
+    starting: 'Starting…',
     startNone: 'no session',
+    startWork: 'Start work',
+    modeLabel: 'Mode',
+    modeWorktree: 'Worktree',
+    modeMain: 'Main branch',
+    branchModeLabel: 'Branch',
+    currentBranch: 'current branch',
+    newBranchOpt: 'new branch',
+    commandLabel: 'Command',
     delete: 'Delete',
     confirmDelete: 'Confirm delete',
     forceDelete: 'Force delete',

packages/web/src/i18n/fr.ts

@@ -143,7 +143,16 @@ const fr: typeof en = {
     branch: 'Branche',
     newBranch: 'créer la branche',
     start: 'Démarrer',
+    starting: 'Démarrage…',
     startNone: 'aucune session',
+    startWork: 'Démarrer le travail',
+    modeLabel: 'Mode',
+    modeWorktree: 'Worktree',
+    modeMain: 'Branche principale',
+    branchModeLabel: 'Branche',
+    currentBranch: 'branche actuelle',
+    newBranchOpt: 'nouvelle branche',
+    commandLabel: 'Commande',
     delete: 'Supprimer',
     confirmDelete: 'Confirmer',
     forceDelete: 'Forcer la suppression',

packages/web/src/stores/worktrees.ts

@@ -7,6 +7,9 @@ import type {
   RepoResponse,
   ReposListResponse,
   RepoSummary,
+  SessionResponse,
+  SessionSummary,
+  StartRepoSessionRequest,
   WorktreeSummary,
   WorktreesListResponse,
 } from '@arboretum/shared';
@@ -104,6 +107,16 @@ export const useWorktreesStore = defineStore('worktrees', () => {
     return res;
   }
 
+  /**
+   * Lance une session sur le checkout principal du repo (« bosser sur la branche principale » sans
+   * worktree). Avec `branch`, le serveur crée/bascule la branche d'abord. La session et le worktree
+   * mis à jour arrivent aussi par WS ; on retourne la session pour permettre la navigation immédiate.
+   */
+  async function startMainSession(repoId: string, req: StartRepoSessionRequest = {}): Promise<SessionSummary> {
+    const res = await api.post<SessionResponse>(`/api/v1/repos/${repoId}/session`, req);
+    return res.session;
+  }
+
   async function deleteWorktree(repoId: string, path: string, force: boolean): Promise<void> {
     await api.delete<{ ok: true }>(`/api/v1/repos/${repoId}/worktrees?path=${encodeURIComponent(path)}&force=${force}`);
     removeWorktreeLocal(path);
@@ -135,6 +148,7 @@ export const useWorktreesStore = defineStore('worktrees', () => {
     discover,
     refreshRepoWorktrees,
     createWorktree,
+    startMainSession,
     deleteWorktree,
     prune,
     startRealtime,