diff --git a/packages/server/scripts/acceptance-p5.mjs b/packages/server/scripts/acceptance-p5.mjs
index 009c0de..f00cffb 100644
--- a/packages/server/scripts/acceptance-p5.mjs
+++ b/packages/server/scripts/acceptance-p5.mjs
@@ -4,7 +4,7 @@
 // group_removed sur le topic 'groups', ajout/retrait de repo, et purge CASCADE de la membership
 // quand le repo est supprimé (PRAGMA foreign_keys = ON).
 import { spawn, execFileSync } from 'node:child_process';
-import { mkdtempSync, rmSync } from 'node:fs';
+import { mkdtempSync, rmSync, writeFileSync } from 'node:fs';
 import { tmpdir } from 'node:os';
 import { join, dirname } from 'node:path';
 import { fileURLToPath } from 'node:url';
@@ -142,6 +142,34 @@ try {
   const pushedSession = await c.waitMsg((m) => m.type === 'session_update' && m.session?.id === gsession.id);
   check('broadcast WS session_update (session de groupe)', !!pushedSession);
 
+  // ---- Worktree de groupe sur une NOUVELLE branche (scénario corrigé : mode auto, plus de -b raté) ----
+  const wtA = await j(`/api/v1/repos/${repoSummary.id}/worktrees`, 'POST', cookie, { branch: 'feature/cross', mode: 'auto', startSession: null });
+  const wtABody = await wtA.json();
+  check('POST /repos/:id/worktrees (branche neuve) → 201 + action=created', wtA.status === 201 && wtABody.action === 'created');
+  const wtB = await j(`/api/v1/repos/${repo2Summary.id}/worktrees`, 'POST', cookie, { branch: 'feature/cross', mode: 'auto', startSession: null });
+  check('POST /repos (2e repo) worktree branche neuve → 201', wtB.status === 201);
+
+  // GET /branches : la nouvelle branche apparaît (alimente le sélecteur de base côté UI).
+  const branchesA = await (await j(`/api/v1/repos/${repoSummary.id}/branches`, 'GET', cookie)).json();
+  check('GET /repos/:id/branches : feature/cross présente', Array.isArray(branchesA.local) && branchesA.local.includes('feature/cross'));
+
+  // session de groupe SUR cette branche → résout les worktrees créés (le cas qui échouait avant).
+  const gsBranch = await j(`/api/v1/groups/${group.id}/session`, 'POST', cookie, { command: 'bash', branch: 'feature/cross' });
+  const gsBranchBody = await gsBranch.json();
+  check('POST /groups/:id/session (branche) → 201 + 2 dirs', gsBranch.status === 201 && gsBranchBody.dirs?.length === 2);
+  await j(`/api/v1/sessions/${gsBranchBody.session.id}`, 'DELETE', cookie);
+
+  // commit : fichier neuf dans le worktree de repo1 puis commit via l'endpoint.
+  writeFileSync(join(wtABody.worktree.path, 'cross.txt'), 'wip\n');
+  const commitRes = await j(`/api/v1/repos/${repoSummary.id}/worktrees/commit`, 'POST', cookie, { path: wtABody.worktree.path, message: 'wip cross' });
+  check('POST /worktrees/commit → 200 + dirty=0', commitRes.status === 200 && (await commitRes.json()).worktree?.git?.dirtyCount === 0);
+
+  // promotion « en principal » : feature/cross devient le checkout principal de repo1, worktree supprimé.
+  const promRes = await j(`/api/v1/repos/${repoSummary.id}/worktrees/promote`, 'POST', cookie, { path: wtABody.worktree.path });
+  check('POST /worktrees/promote → 200', promRes.status === 200);
+  const wtsAfter = await (await j(`/api/v1/repos/${repoSummary.id}/worktrees`, 'GET', cookie)).json();
+  check('promotion : checkout principal désormais sur feature/cross', wtsAfter.worktrees?.find((w) => w.isMain)?.branch === 'feature/cross');
+
   // groupe sans worktree résolu (branche inexistante) → 400.
   const gsBad = await j(`/api/v1/groups/${group.id}/session`, 'POST', cookie, { command: 'bash', branch: 'no/such/branch' });
   check('POST /groups/:id/session branche absente → 400', gsBad.status === 400);
diff --git a/packages/server/src/app.ts b/packages/server/src/app.ts
index f8d18ee..b7b0e9e 100644
--- a/packages/server/src/app.ts
+++ b/packages/server/src/app.ts
@@ -172,7 +172,7 @@ export function buildApp(config: Config, db: Db, serverVersion: string): AppBund
   registerSessionRoutes(app, manager, discovery, db);
   registerRepoRoutes(app, worktrees, db);
   registerGroupRoutes(app, groups, db, worktrees, manager);
-  registerWorktreeRoutes(app, worktrees);
+  registerWorktreeRoutes(app, worktrees, db);
   registerPushRoutes(app, push, db);
   registerSettingsRoutes(app, db, config, serverVersion, push);
   registerFsRoutes(app);
diff --git a/packages/server/src/core/git.ts b/packages/server/src/core/git.ts
index ab7309b..823fb7d 100644
--- a/packages/server/src/core/git.ts
+++ b/packages/server/src/core/git.ts
@@ -2,9 +2,11 @@
 // les chemins/refs utilisateur. Fonctions pures sans état, prenant un cwd déjà validé par l'appelant.
 import { execFile } from 'node:child_process';
 import { resolve, sep } from 'node:path';
-import type { WorktreeGitStatus } from '@arboretum/shared';
+import type { WorktreeGitStatus, WorktreeBranchAction, WorktreeBranchMode } from '@arboretum/shared';
 
 const GIT_TIMEOUT_MS = 10_000;
+// `push` peut dialoguer avec un remote (réseau) : on lui laisse une marge bien plus large.
+const GIT_PUSH_TIMEOUT_MS = 120_000;
 const GIT_MAX_BUFFER = 8 * 1024 * 1024;
 
 interface GitError extends Error {
@@ -12,14 +14,14 @@ interface GitError extends Error {
   code?: number | string;
 }
 
-function git(cwd: string, args: string[]): Promise<string> {
+function git(cwd: string, args: string[], timeoutMs: number = GIT_TIMEOUT_MS): Promise<string> {
   return new Promise((resolveP, reject) => {
     execFile(
       'git',
       args,
       {
         cwd,
-        timeout: GIT_TIMEOUT_MS,
+        timeout: timeoutMs,
         maxBuffer: GIT_MAX_BUFFER,
         // GIT_OPTIONAL_LOCKS=0 : pas de prise de verrou par `status` (perf + concurrence avec une
         // session claude active) ; LC_ALL=C : sortie stable pour le parsing.
@@ -140,6 +142,52 @@ export async function defaultBranch(repoPath: string): Promise<string | null> {
   }
 }
 
+/** Branche courante (nom court) du checkout en `repoPath`, ou null si HEAD détaché. */
+export async function currentBranch(repoPath: string): Promise<string | null> {
+  try {
+    const b = (await git(repoPath, ['rev-parse', '--abbrev-ref', 'HEAD'])).trim();
+    return b === 'HEAD' ? null : b;
+  } catch {
+    return null;
+  }
+}
+
+/** Existence d'une branche, en local (`refs/heads`) et/ou suivie du remote (`refs/remotes/origin`). */
+export async function branchExists(repoPath: string, branch: string): Promise<{ local: boolean; remote: boolean }> {
+  const verify = async (ref: string): Promise<boolean> => {
+    try {
+      await git(repoPath, ['rev-parse', '--verify', '--quiet', ref]);
+      return true;
+    } catch {
+      return false;
+    }
+  };
+  const [local, remote] = await Promise.all([verify(`refs/heads/${branch}`), verify(`refs/remotes/origin/${branch}`)]);
+  return { local, remote };
+}
+
+/** Branches locales + suivies de `origin` (noms courts) + branche par défaut — pour un sélecteur de base. */
+export async function listBranches(repoPath: string): Promise<{ local: string[]; remote: string[]; default: string | null }> {
+  const local: string[] = [];
+  const remote: string[] = [];
+  try {
+    const out = await git(repoPath, ['for-each-ref', '--format=%(refname:short)', 'refs/heads', 'refs/remotes/origin']);
+    for (const line of out.split('\n')) {
+      const name = line.trim();
+      if (!name) continue;
+      if (name.startsWith('origin/')) {
+        const short = name.slice('origin/'.length);
+        if (short && short !== 'HEAD') remote.push(short);
+      } else {
+        local.push(name);
+      }
+    }
+  } catch {
+    /* dépôt sans refs encore (premier commit absent) → listes vides */
+  }
+  return { local, remote, default: await defaultBranch(repoPath) };
+}
+
 export async function listWorktrees(repoPath: string): Promise<ParsedWorktree[]> {
   return parseWorktreePorcelain(await git(repoPath, ['worktree', 'list', '--porcelain']));
 }
@@ -175,19 +223,69 @@ export async function worktreeStatus(worktreePath: string): Promise<WorktreeGitS
   return { ahead, behind, dirtyCount, upstream };
 }
 
+/** Point de départ d'une branche créée : `baseRef` explicite, sinon la branche par défaut du dépôt
+ * (locale ou suivie de `origin`), sinon undefined (git part alors du HEAD courant). */
+async function resolveStartPoint(repoPath: string, baseRef?: string): Promise<string | undefined> {
+  if (baseRef) return baseRef;
+  const def = await defaultBranch(repoPath);
+  if (!def) return undefined;
+  const { local, remote } = await branchExists(repoPath, def);
+  if (local) return def;
+  if (remote) return `origin/${def}`;
+  return undefined;
+}
+
+/**
+ * Crée un worktree en résolvant la branche selon `mode` (voir `WorktreeBranchMode`). Renvoie l'action
+ * effective. En mode `auto`, on choisit checkout / suivi-remote / création selon l'existence réelle de
+ * la branche — indispensable pour les groupes hétérogènes (branche présente dans certains dépôts seulement).
+ */
 export async function addWorktree(
   repoPath: string,
-  opts: { path: string; branch: string; newBranch: boolean; baseRef?: string },
-): Promise<void> {
+  opts: { path: string; branch: string; mode: WorktreeBranchMode; baseRef?: string },
+): Promise<WorktreeBranchAction> {
+  const { local, remote } = await branchExists(repoPath, opts.branch);
+  let action: WorktreeBranchAction;
+  if (opts.mode === 'create') action = 'created';
+  else if (opts.mode === 'checkout') action = local ? 'reused' : 'tracked';
+  else action = local ? 'reused' : remote ? 'tracked' : 'created'; // auto
+
   const args = ['worktree', 'add'];
-  if (opts.newBranch) args.push('-b', opts.branch);
-  args.push('--', opts.path);
-  if (opts.newBranch) {
-    if (opts.baseRef) args.push(opts.baseRef);
+  if (action === 'reused') {
+    args.push('--', opts.path, opts.branch);
+  } else if (action === 'tracked') {
+    args.push('--track', '-b', opts.branch, '--', opts.path, `origin/${opts.branch}`);
   } else {
-    args.push(opts.branch);
+    const start = await resolveStartPoint(repoPath, opts.baseRef);
+    args.push('-b', opts.branch, '--', opts.path);
+    if (start) args.push(start);
   }
   await git(repoPath, args);
+  return action;
+}
+
+/** `git add -A` puis commit. L'appelant garantit qu'il y a quelque chose à committer. */
+export async function commitAll(repoPath: string, message: string): Promise<void> {
+  await git(repoPath, ['add', '-A']);
+  await git(repoPath, ['commit', '-m', message]);
+}
+
+/** Pousse la branche courante. Si aucun upstream n'est configuré : `git push -u origin <branche>`. */
+export async function push(repoPath: string): Promise<void> {
+  let hasUpstream = false;
+  try {
+    await git(repoPath, ['rev-parse', '--abbrev-ref', '--symbolic-full-name', '@{u}']);
+    hasUpstream = true;
+  } catch {
+    hasUpstream = false;
+  }
+  if (hasUpstream) {
+    await git(repoPath, ['push'], GIT_PUSH_TIMEOUT_MS);
+  } else {
+    const branch = await currentBranch(repoPath);
+    if (!branch) throw new Error('cannot push a detached HEAD');
+    await git(repoPath, ['push', '-u', 'origin', branch], GIT_PUSH_TIMEOUT_MS);
+  }
 }
 
 /**
diff --git a/packages/server/src/core/worktree-manager.ts b/packages/server/src/core/worktree-manager.ts
index 94fd50c..2edde00 100644
--- a/packages/server/src/core/worktree-manager.ts
+++ b/packages/server/src/core/worktree-manager.ts
@@ -12,6 +12,8 @@ import type {
   PostCreateHook,
   RepoSummary,
   SessionSummary,
+  WorktreeBranchAction,
+  WorktreeBranchMode,
   WorktreeGitStatus,
   WorktreeSummary,
 } from '@arboretum/shared';
@@ -22,13 +24,16 @@ import { scanForRepos } from './repo-scanner.js';
 import { preTrustProject } from './claude-trust.js';
 import {
   addWorktree,
+  commitAll,
   defaultBranch,
   isDirtyWorktreeError,
   isRepo,
   isSafeAbsolutePath,
   isValidBranchName,
+  listBranches,
   listWorktrees,
   pruneWorktrees,
+  push,
   removeWorktree,
   switchBranch,
   worktreeStatus,
@@ -322,8 +327,8 @@ export class WorktreeManager extends EventEmitter<WorktreeManagerEvents> {
 
   async createWorktree(
     repoId: string,
-    req: { branch: string; newBranch: boolean; baseRef?: string; path?: string; runHooks?: boolean; preTrust?: boolean; startSession?: 'claude' | 'bash' | null },
-  ): Promise<{ worktree: WorktreeSummary; hookResults: HookRunResult[]; session: SessionSummary | null }> {
+    req: { branch: string; mode?: WorktreeBranchMode; baseRef?: string; path?: string; runHooks?: boolean; preTrust?: boolean; startSession?: 'claude' | 'bash' | null },
+  ): Promise<{ worktree: WorktreeSummary; hookResults: HookRunResult[]; session: SessionSummary | null; action: WorktreeBranchAction }> {
     const row = this.getRepoRow(repoId);
     if (!row) throw httpError(404, 'NOT_FOUND', 'No repo with this id');
     if (!isValidBranchName(req.branch)) throw httpError(400, 'BAD_BRANCH', `Invalid branch name: ${req.branch}`);
@@ -332,8 +337,9 @@ export class WorktreeManager extends EventEmitter<WorktreeManagerEvents> {
     if (existsSync(path)) throw httpError(409, 'PATH_EXISTS', `Path already exists: ${path}`);
 
     return this.withLock(repoId, async () => {
+      let action: WorktreeBranchAction;
       try {
-        await addWorktree(row.path, { path, branch: req.branch, newBranch: req.newBranch, ...(req.baseRef ? { baseRef: req.baseRef } : {}) });
+        action = await addWorktree(row.path, { path, branch: req.branch, mode: req.mode ?? 'auto', ...(req.baseRef ? { baseRef: req.baseRef } : {}) });
       } catch (err) {
         throw httpError(400, 'WORKTREE_ADD_FAILED', (err as Error).message);
       }
@@ -352,7 +358,93 @@ export class WorktreeManager extends EventEmitter<WorktreeManagerEvents> {
       if (req.startSession) session = this.ptyManager.spawn({ cwd: path, command: req.startSession });
 
       const worktree = (await this.emitWorktree(row, path)) ?? this.toSummary(row.id, row.path, { path, head: null, branch: req.branch, detached: false, locked: false, prunable: false, bare: false }, { ahead: 0, behind: 0, dirtyCount: 0, upstream: null });
-      return { worktree, hookResults, session };
+      return { worktree, hookResults, session, action };
+    });
+  }
+
+  /** Branches locales/remote + branche par défaut d'un repo — alimente le sélecteur de base côté UI. */
+  async listRepoBranches(repoId: string): Promise<{ local: string[]; remote: string[]; default: string | null }> {
+    const row = this.getRepoRow(repoId);
+    if (!row) throw httpError(404, 'NOT_FOUND', 'No repo with this id');
+    return listBranches(row.path);
+  }
+
+  /** `git add -A` + commit dans le worktree visé (le checkout principal est un worktree valide ici). */
+  async commitWorktree(repoId: string, path: string, message: string): Promise<WorktreeSummary> {
+    const row = this.getRepoRow(repoId);
+    if (!row) throw httpError(404, 'NOT_FOUND', 'No repo with this id');
+    const w = await this.findWorktree(row, path);
+    if (!w) throw httpError(404, 'NOT_FOUND', 'No such worktree under this repo');
+    return this.withLock(repoId, async () => {
+      if ((await worktreeStatus(w.path)).dirtyCount === 0) {
+        throw httpError(409, 'NOTHING_TO_COMMIT', 'Nothing to commit — working tree is clean');
+      }
+      try {
+        await commitAll(w.path, message);
+      } catch (err) {
+        throw httpError(400, 'COMMIT_FAILED', (err as Error).message);
+      }
+      this.factsCache.delete(repoId);
+      return (await this.emitWorktree(row, w.path)) as WorktreeSummary;
+    });
+  }
+
+  /** Pousse la branche du worktree visé (upstream auto si absent). */
+  async pushWorktree(repoId: string, path: string): Promise<WorktreeSummary> {
+    const row = this.getRepoRow(repoId);
+    if (!row) throw httpError(404, 'NOT_FOUND', 'No repo with this id');
+    const w = await this.findWorktree(row, path);
+    if (!w) throw httpError(404, 'NOT_FOUND', 'No such worktree under this repo');
+    return this.withLock(repoId, async () => {
+      try {
+        await push(w.path);
+      } catch (err) {
+        throw httpError(400, 'PUSH_FAILED', (err as Error).message);
+      }
+      this.factsCache.delete(repoId);
+      return (await this.emitWorktree(row, w.path)) as WorktreeSummary;
+    });
+  }
+
+  /**
+   * « Passer en principal » : la branche du worktree devient le checkout principal du dépôt. Une branche
+   * ne pouvant être extraite qu'à un seul endroit, on retire d'abord le worktree (libère la branche) puis
+   * on bascule le checkout principal dessus. Sans merge ni conflit possible. L'ancienne branche principale
+   * est conservée (jamais supprimée). Garde-fous d'arbre sale outrepassables par `force`.
+   */
+  async promoteWorktree(repoId: string, path: string, force = false): Promise<WorktreeSummary | null> {
+    const row = this.getRepoRow(repoId);
+    if (!row) throw httpError(404, 'NOT_FOUND', 'No repo with this id');
+    const w = await this.findWorktree(row, path);
+    if (!w) throw httpError(404, 'NOT_FOUND', 'No such worktree under this repo');
+    if (resolve(w.path) === resolve(row.path)) throw httpError(400, 'IS_MAIN_WORKTREE', 'This is already the main checkout');
+    if (!w.branch || w.detached) throw httpError(400, 'DETACHED_WORKTREE', 'Worktree has no branch to promote (detached HEAD)');
+    const branch = w.branch;
+    return this.withLock(repoId, async () => {
+      if (!force) {
+        if ((await worktreeStatus(w.path)).dirtyCount > 0) {
+          throw httpError(409, 'WORKTREE_DIRTY', 'Worktree has uncommitted changes — commit or pass force');
+        }
+        if ((await worktreeStatus(row.path)).dirtyCount > 0) {
+          throw httpError(409, 'DIRTY_TREE', 'Main checkout has uncommitted changes — commit/stash or pass force');
+        }
+      }
+      try {
+        await removeWorktree(row.path, w.path, force);
+      } catch (err) {
+        if (!force && isDirtyWorktreeError(err)) {
+          throw httpError(409, 'WORKTREE_DIRTY', 'Worktree has uncommitted changes — pass force to promote anyway');
+        }
+        throw httpError(500, 'WORKTREE_REMOVE_FAILED', (err as Error).message);
+      }
+      try {
+        await switchBranch(row.path, { branch, create: false });
+      } catch (err) {
+        throw httpError(500, 'SWITCH_FAILED', (err as Error).message);
+      }
+      this.factsCache.delete(repoId);
+      this.emit('worktree_removed', { repoId, path: w.path });
+      return this.emitWorktree(row, row.path); // le checkout principal est désormais sur `branch`
     });
   }
 
diff --git a/packages/server/src/routes/groups.ts b/packages/server/src/routes/groups.ts
index bcfe889..88fd591 100644
--- a/packages/server/src/routes/groups.ts
+++ b/packages/server/src/routes/groups.ts
@@ -139,7 +139,8 @@ export function registerGroupRoutes(
     }
 
     if (dirs.length === 0) {
-      return reply.status(400).send({ error: { code: 'BAD_REQUEST', message: 'no directory to span (group has no resolvable worktree)' } });
+      const detail = branch ? `no repo has a worktree on branch "${branch}" (create it first)` : 'no repo has a resolvable main checkout';
+      return reply.status(400).send({ error: { code: 'NO_RESOLVABLE_WORKTREE', message: `Cannot start group session: ${detail}` } });
     }
     // cwd = parent commun des repos couverts, chacun relié en --add-dir (P6). Voir resolveGroupCwd.
     const { cwd, addDirs } = resolveGroupCwd(dirs);
diff --git a/packages/server/src/routes/worktrees.ts b/packages/server/src/routes/worktrees.ts
index 5d74b30..10022fe 100644
--- a/packages/server/src/routes/worktrees.ts
+++ b/packages/server/src/routes/worktrees.ts
@@ -1,17 +1,32 @@
 import type { FastifyInstance } from 'fastify';
 import type {
   AdoptWorktreeRequest,
+  CommitWorktreeRequest,
   CreateWorktreeRequest,
   CreateWorktreeResponse,
+  PromoteWorktreeRequest,
+  PushWorktreeRequest,
+  RepoBranchesResponse,
   SessionResponse,
   StartRepoSessionRequest,
+  WorktreeBranchMode,
   WorktreeResponse,
   WorktreesListResponse,
 } from '@arboretum/shared';
 import type { WorktreeManager } from '../core/worktree-manager.js';
+import type { Db } from '../db/index.js';
+import { recordAudit } from '../core/audit-log.js';
 import { sendManagerError } from './repos.js';
 
-export function registerWorktreeRoutes(app: FastifyInstance, wt: WorktreeManager): void {
+/** Mappe l'API (mode prioritaire ; `newBranch` déprécié) vers la stratégie de résolution de branche. */
+function resolveMode(body: { mode?: unknown; newBranch?: unknown }): WorktreeBranchMode {
+  if (body.mode === 'auto' || body.mode === 'create' || body.mode === 'checkout') return body.mode;
+  if (body.newBranch === true) return 'create';
+  if (body.newBranch === false) return 'checkout';
+  return 'auto';
+}
+
+export function registerWorktreeRoutes(app: FastifyInstance, wt: WorktreeManager, db: Db): void {
   app.get('/api/v1/worktrees', async (): Promise<WorktreesListResponse> => ({ worktrees: await wt.listAllWorktrees() }));
 
   app.get('/api/v1/repos/:id/worktrees', async (req): Promise<WorktreesListResponse> => {
@@ -31,7 +46,7 @@ export function registerWorktreeRoutes(app: FastifyInstance, wt: WorktreeManager
     try {
       const out = await wt.createWorktree(id, {
         branch: body.branch,
-        newBranch: body.newBranch !== false, // défaut : créer la branche
+        mode: resolveMode(body), // défaut : auto (détecte créer / checkout / suivi remote)
         ...(body.baseRef !== undefined ? { baseRef: body.baseRef } : {}),
         ...(body.path !== undefined ? { path: body.path } : {}),
         ...(body.runHooks !== undefined ? { runHooks: body.runHooks } : {}),
@@ -45,6 +60,17 @@ export function registerWorktreeRoutes(app: FastifyInstance, wt: WorktreeManager
     }
   });
 
+  // Branches du repo (locales + suivies de origin + défaut) — alimente le sélecteur de base côté UI.
+  app.get('/api/v1/repos/:id/branches', async (req, reply) => {
+    const { id } = req.params as { id: string };
+    try {
+      const out = await wt.listRepoBranches(id);
+      return reply.send(out satisfies RepoBranchesResponse);
+    } catch (err) {
+      return sendManagerError(reply, err);
+    }
+  });
+
   // Session sur le checkout principal (« bosser sur la branche principale » sans worktree),
   // avec création/bascule de branche optionnelle côté serveur.
   app.post('/api/v1/repos/:id/session', async (req, reply) => {
@@ -101,6 +127,57 @@ export function registerWorktreeRoutes(app: FastifyInstance, wt: WorktreeManager
     }
   });
 
+  // Commit (git add -A + commit) dans un worktree (ou le checkout principal).
+  app.post('/api/v1/repos/:id/worktrees/commit', async (req, reply) => {
+    const { id } = req.params as { id: string };
+    const body = req.body as Partial<CommitWorktreeRequest> | null;
+    if (!body || typeof body.path !== 'string') {
+      return reply.status(400).send({ error: { code: 'BAD_REQUEST', message: 'path is required' } });
+    }
+    if (typeof body.message !== 'string' || body.message.trim() === '') {
+      return reply.status(400).send({ error: { code: 'BAD_REQUEST', message: 'message is required' } });
+    }
+    try {
+      const worktree = await wt.commitWorktree(id, body.path, body.message.trim());
+      recordAudit(db, { actor: req.authContext?.tokenId ?? 'unknown', action: 'worktree.commit', resourceId: id, details: { path: body.path } });
+      return reply.send({ worktree } satisfies WorktreeResponse);
+    } catch (err) {
+      return sendManagerError(reply, err);
+    }
+  });
+
+  // Push de la branche d'un worktree (upstream auto si absent).
+  app.post('/api/v1/repos/:id/worktrees/push', async (req, reply) => {
+    const { id } = req.params as { id: string };
+    const body = req.body as Partial<PushWorktreeRequest> | null;
+    if (!body || typeof body.path !== 'string') {
+      return reply.status(400).send({ error: { code: 'BAD_REQUEST', message: 'path is required' } });
+    }
+    try {
+      const worktree = await wt.pushWorktree(id, body.path);
+      recordAudit(db, { actor: req.authContext?.tokenId ?? 'unknown', action: 'worktree.push', resourceId: id, details: { path: body.path } });
+      return reply.send({ worktree } satisfies WorktreeResponse);
+    } catch (err) {
+      return sendManagerError(reply, err);
+    }
+  });
+
+  // Promotion « en principal » : la branche du worktree devient le checkout principal (worktree supprimé).
+  app.post('/api/v1/repos/:id/worktrees/promote', async (req, reply) => {
+    const { id } = req.params as { id: string };
+    const body = req.body as Partial<PromoteWorktreeRequest> | null;
+    if (!body || typeof body.path !== 'string') {
+      return reply.status(400).send({ error: { code: 'BAD_REQUEST', message: 'path is required' } });
+    }
+    try {
+      const worktree = await wt.promoteWorktree(id, body.path, body.force === true);
+      recordAudit(db, { actor: req.authContext?.tokenId ?? 'unknown', action: 'worktree.promote', resourceId: id, details: { path: body.path } });
+      return reply.send({ worktree });
+    } catch (err) {
+      return sendManagerError(reply, err);
+    }
+  });
+
   app.delete('/api/v1/repos/:id/worktrees', async (req, reply) => {
     const { id } = req.params as { id: string };
     const query = req.query as { path?: string; force?: string };
diff --git a/packages/server/test/git.test.ts b/packages/server/test/git.test.ts
index 58d72b6..f2a9a61 100644
--- a/packages/server/test/git.test.ts
+++ b/packages/server/test/git.test.ts
@@ -15,6 +15,10 @@ import {
   pruneWorktrees,
   switchBranch,
   isDirtyWorktreeError,
+  branchExists,
+  currentBranch,
+  listBranches,
+  commitAll,
 } from '../src/core/git.js';
 
 const dirs: string[] = [];
@@ -96,7 +100,7 @@ describe('opérations git (repo tmp réel)', () => {
     const repo = makeTmpRepo();
     const wtPath = join(dirname(repo), `${basename(repo)}-wt-feat`);
     dirs.push(wtPath);
-    await addWorktree(repo, { path: wtPath, branch: 'feat', newBranch: true });
+    await addWorktree(repo, { path: wtPath, branch: 'feat', mode: 'create' });
 
     const list = await listWorktrees(repo);
     const wt = list.find((w) => resolve(w.path) === resolve(wtPath));
@@ -136,9 +140,57 @@ describe('opérations git (repo tmp réel)', () => {
   it('prune retire un worktree dont le dossier a disparu', async () => {
     const repo = makeTmpRepo();
     const wtPath = join(dirname(repo), `${basename(repo)}-wt-gone`);
-    await addWorktree(repo, { path: wtPath, branch: 'gone', newBranch: true });
+    await addWorktree(repo, { path: wtPath, branch: 'gone', mode: 'create' });
     rmSync(wtPath, { recursive: true, force: true }); // suppression "à la main"
     await pruneWorktrees(repo);
     expect((await listWorktrees(repo)).some((w) => resolve(w.path) === resolve(wtPath))).toBe(false);
   });
 });
+
+describe('branche : existence, liste, courante, commit', () => {
+  it('branchExists / currentBranch / listBranches', async () => {
+    const repo = makeTmpRepo();
+    expect(await currentBranch(repo)).toBe('main');
+    expect(await branchExists(repo, 'main')).toEqual({ local: true, remote: false });
+    expect(await branchExists(repo, 'nope')).toEqual({ local: false, remote: false });
+
+    execFileSync('git', ['branch', 'dev'], { cwd: repo });
+    const b = await listBranches(repo);
+    expect(b.local).toContain('main');
+    expect(b.local).toContain('dev');
+    expect(b.remote).toEqual([]);
+  });
+
+  it('commitAll : add -A + commit, fait baisser dirtyCount à 0', async () => {
+    const repo = makeTmpRepo();
+    writeFileSync(join(repo, 'new.txt'), 'hello\n');
+    expect((await worktreeStatus(repo)).dirtyCount).toBeGreaterThan(0);
+    await commitAll(repo, 'add new.txt');
+    expect((await worktreeStatus(repo)).dirtyCount).toBe(0);
+  });
+});
+
+describe('addWorktree : résolution auto (créer / réutiliser)', () => {
+  it('auto crée la branche si absente, la réutilise si présente', async () => {
+    const repo = makeTmpRepo();
+    // branche absente → création (renvoie "created")
+    const wt1 = join(dirname(repo), `${basename(repo)}-wt-feat`);
+    dirs.push(wt1);
+    expect(await addWorktree(repo, { path: wt1, branch: 'feat', mode: 'auto' })).toBe('created');
+    expect((await listWorktrees(repo)).find((w) => resolve(w.path) === resolve(wt1))?.branch).toBe('feat');
+
+    // la même branche existe désormais ; un AUTRE worktree dessus → checkout (renvoie "reused")
+    await removeWorktree(repo, wt1, true); // libère la branche
+    const wt2 = join(dirname(repo), `${basename(repo)}-wt-feat2`);
+    dirs.push(wt2);
+    expect(await addWorktree(repo, { path: wt2, branch: 'feat', mode: 'auto' })).toBe('reused');
+  });
+
+  it('mode create échoue si la branche existe déjà', async () => {
+    const repo = makeTmpRepo();
+    execFileSync('git', ['branch', 'dup'], { cwd: repo });
+    const wt = join(dirname(repo), `${basename(repo)}-wt-dup`);
+    dirs.push(wt);
+    await expect(addWorktree(repo, { path: wt, branch: 'dup', mode: 'create' })).rejects.toBeDefined();
+  });
+});
diff --git a/packages/server/test/worktree-manager.test.ts b/packages/server/test/worktree-manager.test.ts
index 33e0d9d..4eaf820 100644
--- a/packages/server/test/worktree-manager.test.ts
+++ b/packages/server/test/worktree-manager.test.ts
@@ -97,7 +97,8 @@ describe('WorktreeManager', () => {
 
     const wtPath = join(dirname(repo), `${basename(repo)}-wt-feat`);
     dirs.push(wtPath);
-    const out = await wt.createWorktree(r.id, { branch: 'feat', newBranch: true, runHooks: true });
+    const out = await wt.createWorktree(r.id, { branch: 'feat', mode: 'create', runHooks: true });
+    expect(out.action).toBe('created');
 
     expect(resolve(out.worktree.path)).toBe(resolve(wtPath));
     expect(out.worktree.branch).toBe('feat');
@@ -113,7 +114,7 @@ describe('WorktreeManager', () => {
   it('createWorktree : branche invalide → 400', async () => {
     const repo = makeTmpRepo();
     const r = await wt.addRepo({ path: repo });
-    await expect(wt.createWorktree(r.id, { branch: '../evil', newBranch: true })).rejects.toMatchObject({ statusCode: 400 });
+    await expect(wt.createWorktree(r.id, { branch: '../evil', mode: 'create' })).rejects.toMatchObject({ statusCode: 400 });
   });
 
   it('startMainSession : session dans le checkout principal (branche actuelle, sans mutation git)', async () => {
@@ -163,7 +164,7 @@ describe('WorktreeManager', () => {
 
     const wtPath = join(dirname(repo), `${basename(repo)}-wt-x`);
     dirs.push(wtPath);
-    await wt.createWorktree(r.id, { branch: 'x', newBranch: true, runHooks: false });
+    await wt.createWorktree(r.id, { branch: 'x', mode: 'create', runHooks: false });
     writeFileSync(join(wtPath, 'scratch.txt'), 'wip\n'); // worktree sale
 
     await expect(wt.deleteWorktree(r.id, wtPath, false)).rejects.toMatchObject({ statusCode: 409, code: 'WORKTREE_DIRTY' });
@@ -176,7 +177,7 @@ describe('WorktreeManager', () => {
     const r = await wt.addRepo({ path: repo });
     const wtPath = join(dirname(repo), `${basename(repo)}-wt-sess`);
     dirs.push(wtPath);
-    await wt.createWorktree(r.id, { branch: 'sess', newBranch: true, runHooks: false });
+    await wt.createWorktree(r.id, { branch: 'sess', mode: 'create', runHooks: false });
 
     pty.spawn({ cwd: wtPath, command: 'bash' });
     const list = await wt.listRepoWorktrees(r.id, true);
@@ -190,11 +191,49 @@ describe('WorktreeManager', () => {
     const r = await wt.addRepo({ path: repo });
     const wtPath = join(dirname(repo), `${basename(repo)}-wt-busy`);
     dirs.push(wtPath);
-    await wt.createWorktree(r.id, { branch: 'busy', newBranch: true, runHooks: false });
+    await wt.createWorktree(r.id, { branch: 'busy', mode: 'create', runHooks: false });
     pty.spawn({ cwd: wtPath, command: 'bash' });
     await expect(wt.deleteWorktree(r.id, wtPath, false)).rejects.toMatchObject({ statusCode: 409, code: 'SESSION_LIVE_IN_WORKTREE' });
   });
 
+  it('listRepoBranches : renvoie les branches locales (dont main)', async () => {
+    const repo = makeTmpRepo();
+    const r = await wt.addRepo({ path: repo });
+    const b = await wt.listRepoBranches(r.id);
+    expect(b.local).toContain('main');
+  });
+
+  it('commitWorktree : arbre propre → 409 NOTHING_TO_COMMIT ; arbre sale → commit (dirty=0)', async () => {
+    const repo = makeTmpRepo();
+    const r = await wt.addRepo({ path: repo });
+    await expect(wt.commitWorktree(r.id, repo, 'noop')).rejects.toMatchObject({ statusCode: 409, code: 'NOTHING_TO_COMMIT' });
+    writeFileSync(join(repo, 'f.txt'), 'x\n');
+    const w = await wt.commitWorktree(r.id, repo, 'add f');
+    expect(w.git.dirtyCount).toBe(0);
+  });
+
+  it('promoteWorktree : la branche du worktree devient le checkout principal, worktree supprimé, ancienne branche conservée', async () => {
+    const repo = makeTmpRepo();
+    const r = await wt.addRepo({ path: repo });
+    const wtPath = join(dirname(repo), `${basename(repo)}-wt-prom`);
+    dirs.push(wtPath);
+    await wt.createWorktree(r.id, { branch: 'prom', mode: 'create', runHooks: false });
+
+    await wt.promoteWorktree(r.id, wtPath);
+
+    expect(execFileSync('git', ['branch', '--show-current'], { cwd: repo }).toString().trim()).toBe('prom');
+    expect((await wt.listRepoWorktrees(r.id, true)).some((w) => resolve(w.path) === resolve(wtPath))).toBe(false);
+    const branches = await wt.listRepoBranches(r.id);
+    expect(branches.local).toContain('main'); // ancienne branche principale conservée
+    expect(branches.local).toContain('prom');
+  });
+
+  it('promoteWorktree : checkout principal refusé (400 IS_MAIN_WORKTREE)', async () => {
+    const repo = makeTmpRepo();
+    const r = await wt.addRepo({ path: repo });
+    await expect(wt.promoteWorktree(r.id, repo)).rejects.toMatchObject({ statusCode: 400, code: 'IS_MAIN_WORKTREE' });
+  });
+
   it('addRepo renvoie hidden:false ; updateRepo({hidden}) bascule et émet repo_update', async () => {
     const repo = makeTmpRepo();
     const r = await wt.addRepo({ path: repo });
diff --git a/packages/shared/src/api.ts b/packages/shared/src/api.ts
index 9c623bd..abbc07f 100644
--- a/packages/shared/src/api.ts
+++ b/packages/shared/src/api.ts
@@ -109,11 +109,25 @@ export interface HookRunResult {
   output: string;
   durationMs: number;
 }
+/**
+ * Stratégie de résolution de la branche d'un nouveau worktree :
+ * - `auto` (défaut) : détecte l'existence de la branche — checkout si elle existe en local, suivi de
+ *   `origin/<branch>` si elle n'existe que sur le remote, sinon création (`-b`). Robuste pour les
+ *   groupes hétérogènes où la branche peut déjà exister dans certains dépôts mais pas d'autres.
+ * - `create` : force la création (`-b`), échoue si la branche existe déjà.
+ * - `checkout` : force le checkout d'une branche existante, échoue si elle est absente.
+ */
+export type WorktreeBranchMode = 'auto' | 'create' | 'checkout';
+/** Action réellement effectuée par la résolution `auto` (feedback UI). */
+export type WorktreeBranchAction = 'created' | 'reused' | 'tracked';
+
 export interface CreateWorktreeRequest {
   branch: string;
-  /** true : créer la branche (`-b`) ; false : checkout d'une branche existante. */
-  newBranch: boolean;
-  /** point de départ de la nouvelle branche (défaut : HEAD courant du repo). */
+  /** stratégie de résolution de la branche (défaut : `auto`). Voir {@link WorktreeBranchMode}. */
+  mode?: WorktreeBranchMode;
+  /** @deprecated remplacé par `mode` ; mappé : true→create, false→checkout, absent→auto. */
+  newBranch?: boolean;
+  /** point de départ d'une branche créée (défaut : branche par défaut du dépôt, sinon HEAD). */
   baseRef?: string;
   /** chemin cible du worktree (défaut : `<parent>/<repo>-wt-<branch>`). */
   path?: string;
@@ -126,6 +140,35 @@ export interface CreateWorktreeResponse {
   worktree: WorktreeSummary;
   hookResults: HookRunResult[];
   session: SessionSummary | null;
+  /** action effective de la résolution de branche (créée / réutilisée / suivie du remote). */
+  action: WorktreeBranchAction;
+}
+
+/** GET /api/v1/repos/:id/branches — branches locales/remote pour alimenter un sélecteur de base. */
+export interface RepoBranchesResponse {
+  local: string[];
+  remote: string[];
+  /** branche par défaut du dépôt (origin/HEAD), ou null si indéterminée. */
+  default: string | null;
+}
+
+/** POST /api/v1/repos/:id/worktrees/commit — `git add -A` puis commit dans le worktree visé. */
+export interface CommitWorktreeRequest {
+  path: string;
+  message: string;
+}
+/** POST /api/v1/repos/:id/worktrees/push — pousse la branche du worktree (upstream auto si absent). */
+export interface PushWorktreeRequest {
+  path: string;
+}
+/**
+ * POST /api/v1/repos/:id/worktrees/promote — « passer en principal » : la branche du worktree devient
+ * le checkout principal du dépôt (le worktree est supprimé, l'ancienne branche principale est conservée).
+ */
+export interface PromoteWorktreeRequest {
+  path: string;
+  /** outrepasse les garde-fous d'arbre sale (worktree/checkout principal). */
+  force?: boolean;
 }
 export interface AdoptWorktreeRequest {
   path: string;
diff --git a/packages/web/src/components/GroupSessionModal.vue b/packages/web/src/components/GroupSessionModal.vue
index 9cda131..8f57ff1 100644
--- a/packages/web/src/components/GroupSessionModal.vue
+++ b/packages/web/src/components/GroupSessionModal.vue
@@ -21,21 +21,20 @@
           </div>
         </div>
 
-        <!-- mode feature : branche commune créée dans chaque repo -->
+        <!-- mode feature : branche commune créée (ou réutilisée si déjà présente) dans chaque repo -->
         <template v-if="mode === 'feature'">
           <label class="flex flex-col gap-1 text-xs text-zinc-400">
             {{ t('crossRepo.branchLabel') }}
             <input v-model="branch" class="input font-mono" :placeholder="t('crossRepo.branchPlaceholder')" :required="mode === 'feature'" />
+            <span class="text-[11px] text-zinc-500">{{ t('crossRepo.branchHint') }}</span>
+          </label>
+          <label class="flex flex-col gap-1 text-xs text-zinc-400">
+            {{ t('crossRepo.baseRefLabel') }}
+            <input v-model="baseRef" class="input font-mono" list="group-base-branches" :placeholder="t('crossRepo.baseRefPlaceholder')" />
+            <datalist id="group-base-branches">
+              <option v-for="b in baseBranchOptions" :key="b" :value="b" />
+            </datalist>
           </label>
-          <div class="flex flex-wrap items-end gap-3">
-            <label class="flex items-center gap-1.5 text-xs text-zinc-400">
-              <input v-model="newBranch" type="checkbox" /> {{ t('crossRepo.newBranch') }}
-            </label>
-            <label class="flex flex-col gap-1 text-xs text-zinc-400">
-              {{ t('crossRepo.baseRefLabel') }}
-              <input v-model="baseRef" class="input font-mono" placeholder="HEAD" />
-            </label>
-          </div>
         </template>
 
         <label class="flex flex-col gap-1 text-xs text-zinc-400">
@@ -78,11 +77,12 @@
 </template>
 
 <script setup lang="ts">
-import { computed, ref } from 'vue';
+import { computed, onMounted, ref } from 'vue';
 import { useRouter } from 'vue-router';
 import { useI18n } from 'vue-i18n';
-import type { RepoSummary } from '@arboretum/shared';
+import type { RepoBranchesResponse, RepoSummary } from '@arboretum/shared';
 import { useGroupsStore, type CrossRepoResult, type GroupFeatureOutcome } from '../stores/groups';
+import { useWorktreesStore } from '../stores/worktrees';
 import { useToastsStore } from '../stores/toasts';
 
 const props = defineProps<{ groupId: string; repos: RepoSummary[] }>();
@@ -91,12 +91,29 @@ const emit = defineEmits<{ close: [] }>();
 const { t } = useI18n();
 const router = useRouter();
 const groups = useGroupsStore();
+const worktrees = useWorktreesStore();
 const toasts = useToastsStore();
 
 const mode = ref<'feature' | 'main'>('feature');
 const branch = ref('');
-const newBranch = ref(true);
 const baseRef = ref('');
+
+// Sélecteur de branche de base : branches du 1er repo du groupe (indicatif ; vide → défaut serveur par repo).
+const branches = ref<RepoBranchesResponse | null>(null);
+const baseBranchOptions = computed<string[]>(() => {
+  const b = branches.value;
+  if (!b) return [];
+  return Array.from(new Set([...(b.default ? [b.default] : []), ...b.local, ...b.remote]));
+});
+onMounted(async () => {
+  const first = props.repos[0];
+  if (!first) return;
+  try {
+    branches.value = await worktrees.fetchBranches(first.id);
+  } catch {
+    /* le sélecteur de base est facultatif */
+  }
+});
 const command = ref<'claude' | 'bash'>('claude');
 const wtResults = ref<Record<string, CrossRepoResult>>({});
 const outcome = ref<GroupFeatureOutcome | null>(null);
@@ -136,7 +153,7 @@ async function onSubmit(): Promise<void> {
       {
         command: command.value,
         ...(mode.value === 'feature'
-          ? { branch: branch.value.trim(), newBranch: newBranch.value, ...(baseRef.value.trim() ? { baseRef: baseRef.value.trim() } : {}) }
+          ? { branch: branch.value.trim(), ...(baseRef.value.trim() ? { baseRef: baseRef.value.trim() } : {}) }
           : {}),
       },
       (result) => {
diff --git a/packages/web/src/components/RepoSection.vue b/packages/web/src/components/RepoSection.vue
index a6e8fa7..bced9ed 100644
--- a/packages/web/src/components/RepoSection.vue
+++ b/packages/web/src/components/RepoSection.vue
@@ -27,12 +27,19 @@
       </div>
 
       <div class="flex flex-wrap items-end gap-2">
-        <!-- mode worktree : branche + créer/existante -->
+        <!-- mode worktree : branche (créée si absente, réutilisée si présente) + branche de base + session -->
         <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.baseRefLabel') }}
+            <input v-model="baseRef" class="input font-mono" :list="datalistId" :placeholder="t('worktrees.baseRefPlaceholder')" />
+            <datalist :id="datalistId">
+              <option v-for="b in baseBranchOptions" :key="b" :value="b" />
+            </datalist>
+          </label>
           <label class="flex flex-col gap-1 text-xs text-zinc-400">
             {{ t('worktrees.start') }}
             <select v-model="startSession" class="input">
@@ -41,7 +48,6 @@
               <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 -->
@@ -81,10 +87,10 @@
 </template>
 
 <script setup lang="ts">
-import { computed, ref } from 'vue';
+import { computed, ref, watch } from 'vue';
 import { useI18n } from 'vue-i18n';
 import { Eye, EyeOff, Plus, Scissors, Trash2 } from '@lucide/vue';
-import type { RepoSummary } from '@arboretum/shared';
+import type { RepoBranchesResponse, RepoSummary } from '@arboretum/shared';
 import { useWorktreesStore } from '../stores/worktrees';
 import { useWorktreeView } from '../composables/useWorktreeView';
 import { useToastsStore } from '../stores/toasts';
@@ -103,13 +109,30 @@ 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 baseRef = ref('');
 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);
 
+// Sélecteur de branche de base (chargé paresseusement à l'ouverture du formulaire).
+const branches = ref<RepoBranchesResponse | null>(null);
+const datalistId = computed(() => `wt-base-branches-${props.repo.id}`);
+const baseBranchOptions = computed<string[]>(() => {
+  const b = branches.value;
+  if (!b) return [];
+  return Array.from(new Set([...(b.default ? [b.default] : []), ...b.local, ...b.remote]));
+});
+watch(creating, async (open) => {
+  if (!open || branches.value) return;
+  try {
+    branches.value = await store.fetchBranches(props.repo.id);
+  } catch {
+    /* le sélecteur de base est facultatif */
+  }
+});
+
 // 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() !== '',
@@ -120,7 +143,12 @@ async function onCreate(): Promise<void> {
   error.value = null;
   try {
     if (mode.value === 'worktree') {
-      await store.createWorktree(props.repo.id, { branch: branch.value.trim(), newBranch: newBranch.value, startSession: startSession.value });
+      await store.createWorktree(props.repo.id, {
+        branch: branch.value.trim(),
+        mode: 'auto', // détecte créer / checkout / suivi remote
+        ...(baseRef.value.trim() ? { baseRef: baseRef.value.trim() } : {}),
+        startSession: startSession.value,
+      });
       toasts.success(t('toast.worktreeCreated'));
     } else {
       // bosser sur la branche principale : session dans le checkout principal, avec création de branche optionnelle.
@@ -131,6 +159,7 @@ async function onCreate(): Promise<void> {
       toasts.success(t('toast.sessionCreated'));
     }
     branch.value = '';
+    baseRef.value = '';
     creating.value = false;
   } catch (err) {
     error.value = err instanceof Error ? err.message : String(err);
diff --git a/packages/web/src/components/TerminalCell.vue b/packages/web/src/components/TerminalCell.vue
index 320c245..f0c58b8 100644
--- a/packages/web/src/components/TerminalCell.vue
+++ b/packages/web/src/components/TerminalCell.vue
@@ -12,6 +12,14 @@
         {{ t('groups.spanBadge', spannedCount) }}
       </span>
       <span class="ml-auto shrink-0 font-mono text-[11px] text-zinc-500">{{ session.command }}</span>
+      <button
+        class="shrink-0 rounded p-0.5 text-zinc-500 transition-colors hover:text-zinc-200"
+        :aria-label="maximized ? t('terminal.restore') : t('terminal.maximize')"
+        :title="maximized ? t('terminal.restore') : t('terminal.maximize')"
+        @click="emit('toggle-maximize')"
+      >
+        <component :is="maximized ? Minimize2 : Maximize2" class="h-3.5 w-3.5" />
+      </button>
     </header>
     <DialogPrompt v-if="isWaiting" :session="session" class="px-2 pt-2" />
     <div class="min-h-0 flex-1">
@@ -23,13 +31,15 @@
 <script setup lang="ts">
 import { computed } from 'vue';
 import { useI18n } from 'vue-i18n';
+import { Maximize2, Minimize2 } from '@lucide/vue';
 import type { SessionSummary } from '@arboretum/shared';
 import { useWorktreesStore } from '../stores/worktrees';
 import SessionStateBadge from './SessionStateBadge.vue';
 import DialogPrompt from './DialogPrompt.vue';
 import TerminalView from './TerminalView.vue';
 
-const props = defineProps<{ session: SessionSummary }>();
+const props = defineProps<{ session: SessionSummary; maximized?: boolean }>();
+const emit = defineEmits<{ 'toggle-maximize': [] }>();
 const worktrees = useWorktreesStore();
 const { t } = useI18n();
 
diff --git a/packages/web/src/components/TerminalGrid.vue b/packages/web/src/components/TerminalGrid.vue
index 0e0abc0..44b83f0 100644
--- a/packages/web/src/components/TerminalGrid.vue
+++ b/packages/web/src/components/TerminalGrid.vue
@@ -2,19 +2,24 @@
   <div class="flex flex-col gap-2">
     <p v-if="sessions.length === 0" class="text-sm text-zinc-500">{{ t('groups.gridEmpty') }}</p>
     <template v-else>
-      <p v-if="sessions.length > MAX_CELLS" class="text-xs text-amber-400">
+      <p v-if="!activeMax && sessions.length > MAX_CELLS" class="text-xs text-amber-400">
         {{ t('groups.gridCapped', { shown: MAX_CELLS, total: sessions.length }) }}
       </p>
       <!-- une seule socket WS multiplexe tous les terminaux ; cap dur pour préserver GPU/canaux.
            Sur mobile la grille retombe à une colonne (empilement). Hauteur relative au viewport
            (dvh) : terminaux grands sur PC, exploitables sur mobile ; xterm re-fit via ResizeObserver.
            Plancher min-h-80 pour les fenêtres courtes. -->
-      <div class="grid grid-cols-1 gap-3 lg:grid-cols-2 2xl:grid-cols-3">
+      <!-- une cellule maximisée → plein cadre ; sinon la grille responsive -->
+      <div v-if="activeMax" class="grid grid-cols-1">
+        <TerminalCell :session="activeMax" maximized class="h-[calc(100dvh-8rem)] min-h-80" @toggle-maximize="toggleMax(activeMax.id)" />
+      </div>
+      <div v-else class="grid grid-cols-1 gap-3 lg:grid-cols-2 2xl:grid-cols-3">
         <TerminalCell
           v-for="s in shown"
           :key="s.id"
           :session="s"
           class="h-[68dvh] min-h-80 lg:h-[calc((100dvh-9rem)/2)]"
+          @toggle-maximize="toggleMax(s.id)"
         />
       </div>
     </template>
@@ -22,7 +27,7 @@
 </template>
 
 <script setup lang="ts">
-import { computed } from 'vue';
+import { computed, ref } from 'vue';
 import { useI18n } from 'vue-i18n';
 import type { SessionSummary } from '@arboretum/shared';
 import TerminalCell from './TerminalCell.vue';
@@ -32,4 +37,14 @@ const { t } = useI18n();
 
 const MAX_CELLS = 6;
 const shown = computed(() => props.sessions.slice(0, MAX_CELLS));
+
+// Maximisation d'une cellule au choix (état purement présentation, local à la grille). Si la session
+// maximisée disparaît (terminée), on retombe automatiquement sur la grille.
+const maximizedId = ref<string | null>(null);
+function toggleMax(id: string): void {
+  maximizedId.value = maximizedId.value === id ? null : id;
+}
+const activeMax = computed<SessionSummary | null>(() =>
+  maximizedId.value ? (shown.value.find((s) => s.id === maximizedId.value) ?? null) : null,
+);
 </script>
diff --git a/packages/web/src/components/WorktreeCard.vue b/packages/web/src/components/WorktreeCard.vue
index d5f1d3b..f559d33 100644
--- a/packages/web/src/components/WorktreeCard.vue
+++ b/packages/web/src/components/WorktreeCard.vue
@@ -62,6 +62,41 @@
       </div>
     </div>
 
+    <!-- actions git : commit / push / promotion en principal (sans ouvrir le terminal) -->
+    <div v-if="canPush || worktree.git.dirtyCount || canPromote" class="mt-1 flex flex-wrap items-center gap-2">
+      <form v-if="committingOpen" class="flex flex-wrap items-center gap-1" @submit.prevent="onCommit">
+        <input v-model="commitMessage" class="input w-44 text-xs" :placeholder="t('worktrees.commitPlaceholder')" />
+        <button type="submit" class="btn-primary text-xs" :disabled="!!gitBusy || commitMessage.trim() === ''">
+          {{ gitBusy === 'commit' ? t('worktrees.committing') : t('worktrees.commit') }}
+        </button>
+        <button type="button" class="btn text-xs" @click="committingOpen = false">{{ t('common.cancel') }}</button>
+      </form>
+      <button v-else-if="worktree.git.dirtyCount" class="btn text-xs" :disabled="!!gitBusy" @click="committingOpen = true">
+        {{ t('worktrees.commit') }}
+      </button>
+
+      <button v-if="canPush" class="btn text-xs" :disabled="!!gitBusy" @click="onPush">
+        {{ gitBusy === 'push' ? t('worktrees.pushing') : t('worktrees.push') }}<span v-if="worktree.git.ahead"> ↑{{ worktree.git.ahead }}</span>
+      </button>
+
+      <button v-if="canPromote && !promoteConfirming" class="btn text-xs" :disabled="!!gitBusy" @click="promoteConfirming = true">
+        {{ t('worktrees.promote') }}
+      </button>
+
+      <span v-if="gitError" class="text-xs text-amber-400">{{ gitError }}</span>
+    </div>
+
+    <!-- confirmation explicite de la promotion (action destructive : ce worktree sera supprimé) -->
+    <div v-if="promoteConfirming" class="mt-1 rounded border border-amber-700/40 bg-amber-950/20 p-2 text-xs text-amber-200">
+      {{ promoteConfirmText }}
+      <div class="mt-1 flex items-center gap-2">
+        <button class="btn-primary text-xs" :disabled="!!gitBusy" @click="onPromote">
+          {{ gitBusy === 'promote' ? t('worktrees.promoting') : forcePromoteNeeded ? t('worktrees.forcePromote') : t('worktrees.promote') }}
+        </button>
+        <button class="btn text-xs" @click="cancelPromote">{{ t('common.cancel') }}</button>
+      </div>
+    </div>
+
     <!-- réponse rapide aux dialogues des sessions corrélées en attente (sans ouvrir le terminal) -->
     <DialogPrompt v-for="ws in waitingSessions" :key="`dlg-${ws.id}`" :session="ws" class="mt-2" />
   </div>
@@ -135,6 +170,73 @@ const branchLabel = computed(() =>
   props.worktree.branch ?? (props.worktree.detached ? `${t('worktrees.detached')} ${props.worktree.head.slice(0, 7)}` : '—'),
 );
 
+// --- actions git : commit / push / promotion en principal ---
+const gitBusy = ref<null | 'commit' | 'push' | 'promote'>(null);
+const gitError = ref<string | null>(null);
+const committingOpen = ref(false);
+const commitMessage = ref('');
+const promoteConfirming = ref(false);
+const forcePromoteNeeded = ref(false);
+
+const canPush = computed(() => !!props.worktree.branch && !props.worktree.detached);
+const canPromote = computed(() => !props.worktree.isMain && !!props.worktree.branch && !props.worktree.detached);
+const promoteConfirmText = computed(() => t('worktrees.promoteConfirm', { branch: props.worktree.branch ?? '' }));
+
+function gitMsg(err: unknown): string {
+  return err instanceof Error ? err.message : String(err);
+}
+function cancelPromote(): void {
+  promoteConfirming.value = false;
+  forcePromoteNeeded.value = false;
+}
+
+async function onCommit(): Promise<void> {
+  if (gitBusy.value || commitMessage.value.trim() === '') return;
+  gitBusy.value = 'commit';
+  gitError.value = null;
+  try {
+    await store.commitWorktree(props.worktree.repoId, props.worktree.path, commitMessage.value.trim());
+    committingOpen.value = false;
+    commitMessage.value = '';
+  } catch (err) {
+    gitError.value = gitMsg(err);
+  } finally {
+    gitBusy.value = null;
+  }
+}
+
+async function onPush(): Promise<void> {
+  if (gitBusy.value) return;
+  gitBusy.value = 'push';
+  gitError.value = null;
+  try {
+    await store.pushWorktree(props.worktree.repoId, props.worktree.path);
+  } catch (err) {
+    gitError.value = gitMsg(err);
+  } finally {
+    gitBusy.value = null;
+  }
+}
+
+async function onPromote(): Promise<void> {
+  if (gitBusy.value) return;
+  gitBusy.value = 'promote';
+  gitError.value = null;
+  try {
+    await store.promoteWorktree(props.worktree.repoId, props.worktree.path, forcePromoteNeeded.value);
+    // succès : la branche est passée en principal et ce worktree est supprimé → la carte se démonte.
+  } catch (err) {
+    if (err instanceof ApiError && err.status === 409) {
+      forcePromoteNeeded.value = true; // arbre modifié → proposer la promotion forcée
+      gitError.value = err.message;
+    } else {
+      gitError.value = gitMsg(err);
+    }
+  } finally {
+    gitBusy.value = null;
+  }
+}
+
 function reset(): void {
   confirming.value = false;
   forceNeeded.value = false;
diff --git a/packages/web/src/i18n/en.ts b/packages/web/src/i18n/en.ts
index 2059443..87cd580 100644
--- a/packages/web/src/i18n/en.ts
+++ b/packages/web/src/i18n/en.ts
@@ -113,14 +113,15 @@ export default {
     modeMain: 'Main checkouts',
     branchLabel: 'Branch name',
     branchPlaceholder: 'feature/…',
-    newBranch: 'create branch',
-    baseRefLabel: 'Base ref (optional)',
+    branchHint: 'Created where missing, reused where it already exists in the repo.',
+    baseRefLabel: 'Base branch (optional)',
+    baseRefPlaceholder: "repo's default branch",
     commandLabel: 'Session',
     reposLabel: 'Repos in this session',
     launch: 'Launch session',
     launching: 'Launching…',
     close: 'Close',
-    ok: 'worktree created',
+    ok: 'worktree ready',
     error: 'failed',
     skippedLabel: 'skipped',
     done: 'Group session started.',
@@ -146,6 +147,8 @@ export default {
     creating: 'Creating…',
     branch: 'Branch',
     newBranch: 'create branch',
+    baseRefLabel: 'Base branch',
+    baseRefPlaceholder: 'default branch',
     start: 'Start',
     starting: 'Starting…',
     startNone: 'no session',
@@ -161,6 +164,16 @@ export default {
     confirmDelete: 'Confirm delete',
     forceDelete: 'Force delete',
     prune: 'Prune',
+    commit: 'Commit',
+    commitPlaceholder: 'Commit message',
+    committing: 'Committing…',
+    push: 'Push',
+    pushing: 'Pushing…',
+    promote: 'Make main',
+    promoting: 'Promoting…',
+    promoteConfirm:
+      'Branch “{branch}” will become the repository’s main checkout; this worktree will be removed (the previous main branch is kept). Continue?',
+    forcePromote: 'Force (dirty tree)',
     main: 'main',
     detached: 'detached',
     locked: 'locked',
@@ -176,6 +189,8 @@ export default {
     notAttachable: 'This session runs outside Arboretum — fork it to interact, or resume it once it has stopped.',
     fullscreen: 'Fullscreen',
     exitFullscreen: 'Exit fullscreen',
+    maximize: 'Maximize',
+    restore: 'Restore',
   },
   push: {
     enable: 'Enable notifications',
diff --git a/packages/web/src/i18n/fr.ts b/packages/web/src/i18n/fr.ts
index 6ec919f..746e2ec 100644
--- a/packages/web/src/i18n/fr.ts
+++ b/packages/web/src/i18n/fr.ts
@@ -115,14 +115,15 @@ const fr: typeof en = {
     modeMain: 'Checkouts principaux',
     branchLabel: 'Nom de branche',
     branchPlaceholder: 'feature/…',
-    newBranch: 'créer la branche',
-    baseRefLabel: 'Réf. de base (optionnel)',
+    branchHint: 'Créée si absente, réutilisée si déjà présente dans le dépôt.',
+    baseRefLabel: 'Branche de base (optionnel)',
+    baseRefPlaceholder: 'branche par défaut du dépôt',
     commandLabel: 'Session',
     reposLabel: 'Dépôts de la session',
     launch: 'Lancer la session',
     launching: 'Lancement…',
     close: 'Fermer',
-    ok: 'worktree créé',
+    ok: 'worktree prêt',
     error: 'échec',
     skippedLabel: 'ignoré',
     done: 'Session de groupe démarrée.',
@@ -148,6 +149,8 @@ const fr: typeof en = {
     creating: 'Création…',
     branch: 'Branche',
     newBranch: 'créer la branche',
+    baseRefLabel: 'Branche de base',
+    baseRefPlaceholder: 'branche par défaut',
     start: 'Démarrer',
     starting: 'Démarrage…',
     startNone: 'aucune session',
@@ -163,6 +166,16 @@ const fr: typeof en = {
     confirmDelete: 'Confirmer',
     forceDelete: 'Forcer la suppression',
     prune: 'Élaguer',
+    commit: 'Commit',
+    commitPlaceholder: 'Message de commit',
+    committing: 'Commit…',
+    push: 'Push',
+    pushing: 'Push…',
+    promote: 'Passer en principal',
+    promoting: 'Promotion…',
+    promoteConfirm:
+      'La branche « {branch} » deviendra le checkout principal du dépôt ; ce worktree sera supprimé (l’ancienne branche principale est conservée). Continuer ?',
+    forcePromote: 'Forcer (arbre modifié)',
     main: 'principal',
     detached: 'détaché',
     locked: 'verrouillé',
@@ -179,6 +192,8 @@ const fr: typeof en = {
       'Cette session tourne hors d’Arboretum — dupliquez-la pour interagir, ou reprenez-la une fois arrêtée.',
     fullscreen: 'Plein écran',
     exitFullscreen: 'Quitter le plein écran',
+    maximize: 'Agrandir',
+    restore: 'Réduire',
   },
   push: {
     enable: 'Activer les notifications',
diff --git a/packages/web/src/stores/groups.ts b/packages/web/src/stores/groups.ts
index eef29c4..ebb0274 100644
--- a/packages/web/src/stores/groups.ts
+++ b/packages/web/src/stores/groups.ts
@@ -28,9 +28,9 @@ export interface CrossRepoResult {
 /** Options de lancement d'une session de groupe (P6). */
 export interface GroupFeatureOptions {
   command: 'claude' | 'bash';
-  /** présent → crée le worktree de cette branche dans chaque repo puis relie ; absent → checkouts principaux. */
+  /** présent → crée/réutilise le worktree de cette branche dans chaque repo puis relie ; absent → checkouts principaux. */
   branch?: string;
-  newBranch?: boolean;
+  /** branche de base d'une branche créée (défaut serveur : branche par défaut du dépôt). */
   baseRef?: string;
 }
 
@@ -157,7 +157,7 @@ export const useGroupsStore = defineStore('groups', () => {
           try {
             const res = await wt.createWorktree(repoId, {
               branch,
-              newBranch: opts.newBranch ?? true,
+              mode: 'auto', // détecte créer / checkout / suivi remote selon l'existence par dépôt
               ...(opts.baseRef ? { baseRef: opts.baseRef } : {}),
               startSession: null,
             });
@@ -176,6 +176,11 @@ export const useGroupsStore = defineStore('groups', () => {
         }),
       );
     }
+    // Mode feature : si AUCUN worktree n'a pu être créé/résolu, ne pas tenter la session (elle
+    // échouerait en « no resolvable worktree » et masquerait les vraies erreurs par dépôt).
+    if (opts.branch && worktreeResults.length > 0 && !worktreeResults.some((r) => r.status === 'ok')) {
+      return { worktreeResults, session: null, dirs: [], skipped: [] };
+    }
     const res = await createGroupSession(groupId, {
       command: opts.command,
       ...(opts.branch ? { branch: opts.branch } : {}),
diff --git a/packages/web/src/stores/worktrees.ts b/packages/web/src/stores/worktrees.ts
index c2543cd..b54ff29 100644
--- a/packages/web/src/stores/worktrees.ts
+++ b/packages/web/src/stores/worktrees.ts
@@ -4,12 +4,14 @@ import type {
   CreateWorktreeRequest,
   CreateWorktreeResponse,
   DiscoverReposResponse,
+  RepoBranchesResponse,
   RepoResponse,
   ReposListResponse,
   RepoSummary,
   SessionResponse,
   SessionSummary,
   StartRepoSessionRequest,
+  WorktreeResponse,
   WorktreeSummary,
   WorktreesListResponse,
 } from '@arboretum/shared';
@@ -127,6 +129,32 @@ export const useWorktreesStore = defineStore('worktrees', () => {
     await refreshRepoWorktrees(repoId);
   }
 
+  /** Branches du repo (locales/remote + défaut) pour le sélecteur de branche de base. */
+  async function fetchBranches(repoId: string): Promise<RepoBranchesResponse> {
+    return api.get<RepoBranchesResponse>(`/api/v1/repos/${repoId}/branches`);
+  }
+
+  /** Commit (add -A + commit) dans un worktree ; le worktree mis à jour arrive aussi par WS. */
+  async function commitWorktree(repoId: string, path: string, message: string): Promise<WorktreeSummary> {
+    const res = await api.post<WorktreeResponse>(`/api/v1/repos/${repoId}/worktrees/commit`, { path, message });
+    upsertWorktree(res.worktree);
+    return res.worktree;
+  }
+
+  /** Push de la branche d'un worktree (upstream auto si absent). */
+  async function pushWorktree(repoId: string, path: string): Promise<WorktreeSummary> {
+    const res = await api.post<WorktreeResponse>(`/api/v1/repos/${repoId}/worktrees/push`, { path });
+    upsertWorktree(res.worktree);
+    return res.worktree;
+  }
+
+  /** « Passer en principal » : la branche du worktree devient le checkout principal (worktree supprimé). */
+  async function promoteWorktree(repoId: string, path: string, force = false): Promise<void> {
+    await api.post<{ worktree: WorktreeSummary | null }>(`/api/v1/repos/${repoId}/worktrees/promote`, { path, force });
+    removeWorktreeLocal(path);
+    await refreshRepoWorktrees(repoId);
+  }
+
   function startRealtime(): void {
     unsubscribe ??= wsClient.subscribeWorktrees(onEvent);
   }
@@ -151,6 +179,10 @@ export const useWorktreesStore = defineStore('worktrees', () => {
     startMainSession,
     deleteWorktree,
     prune,
+    fetchBranches,
+    commitWorktree,
+    pushWorktree,
+    promoteWorktree,
     startRealtime,
     stopRealtime,
   };