feat(acp): SessionService.Create issues system MCP token in tx

- InTx wraps InsertSession + IssueSystemTokenWithTx (spec §6.1 atomic guarantee)
- Tx failure -> releaseOnFailure (worktree rollback)
- Spawn called with extraEnv = ACW_MCP_TOKEN + ACW_MCP_URL
- Spawn failure -> RevokeBySession (idempotent) + releaseOnFailure
- app.go SessionService construction updated with mcpTokens + config
- Unit tests: token issuance happy path + rollback on token failure

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/acp/session_service.go

@@ -10,17 +10,21 @@ import (
 	"time"
 
 	"github.com/google/uuid"
+	"github.com/jackc/pgx/v5"
 
 	"github.com/yan1h/agent-coding-workflow/internal/audit"
 	"github.com/yan1h/agent-coding-workflow/internal/infra/errs"
+	"github.com/yan1h/agent-coding-workflow/internal/mcp"
 	"github.com/yan1h/agent-coding-workflow/internal/project"
 	"github.com/yan1h/agent-coding-workflow/internal/workspace"
 )
 
-// SessionServiceConfig 是 service 的限流配置（从 AcpConfig 派生）。
+// SessionServiceConfig 是 service 的限流 + MCP 配置（从 AcpConfig / MCPConfig 派生）。
 type SessionServiceConfig struct {
 	MaxActiveGlobal  int
 	MaxActivePerUser int
+	SystemTokenTTL   time.Duration
+	MCPPublicURL     string
 }
 
 // ProjectAccess 是 acp 模块对 project 模块的窄接口；adapter 在 app.go 实现。
@@ -31,24 +35,25 @@ type ProjectAccess interface {
 }
 
 type sessionService struct {
-	repo   Repository
-	wsSvc  workspace.WorkspaceService
-	wtSvc  workspace.WorktreeService
-	wsRepo workspace.Repository
-	pa     ProjectAccess
-	sup    *Supervisor
-	audit  audit.Recorder
-	cfg    SessionServiceConfig
+	repo      Repository
+	wsSvc     workspace.WorkspaceService
+	wtSvc     workspace.WorktreeService
+	wsRepo    workspace.Repository
+	pa        ProjectAccess
+	sup       *Supervisor
+	audit     audit.Recorder
+	cfg       SessionServiceConfig
+	mcpTokens mcp.TokenService // spec §6.1 — system token issuance
 }
 
 // NewSessionService 构造 SessionService。
 func NewSessionService(repo Repository, wsSvc workspace.WorkspaceService,
 	wtSvc workspace.WorktreeService, wsRepo workspace.Repository,
 	pa ProjectAccess, sup *Supervisor, rec audit.Recorder,
-	cfg SessionServiceConfig) SessionService {
+	cfg SessionServiceConfig, mcpTokens mcp.TokenService) SessionService {
 	return &sessionService{
 		repo: repo, wsSvc: wsSvc, wtSvc: wtSvc, wsRepo: wsRepo,
-		pa: pa, sup: sup, audit: rec, cfg: cfg,
+		pa: pa, sup: sup, audit: rec, cfg: cfg, mcpTokens: mcpTokens,
 	}
 }
 
@@ -192,7 +197,7 @@ func (s *sessionService) Create(ctx context.Context, c Caller, in CreateSessionI
 		}
 	}
 
-	// 7. INSERT
+	// 7. INSERT acp_sessions + system MCP token（spec §6.1 atomic guarantee）
 	sess := &Session{
 		ID: sessionID, WorkspaceID: ws.ID, ProjectID: ws.ProjectID,
 		AgentKindID: kind.ID, UserID: c.UserID,
@@ -200,10 +205,32 @@ func (s *sessionService) Create(ctx context.Context, c Caller, in CreateSessionI
 		Branch: branch, CwdPath: cwdPath, IsMainWorktree: isMain,
 		Status: SessionStarting,
 	}
-	out, err := s.repo.InsertSession(ctx, sess)
-	if err != nil {
+	var (
+		out      *Session
+		tokenRes mcp.IssueResult
+	)
+	txErr := s.repo.InTx(ctx, func(txCtx context.Context, tx pgx.Tx) error {
+		inserted, err := s.repo.WithTx(tx).InsertSession(txCtx, sess)
+		if err != nil {
+			return err
+		}
+		out = inserted
+
+		res, err := s.mcpTokens.IssueSystemTokenWithTx(txCtx, tx, mcp.IssueSystemTokenInput{
+			UserID:       c.UserID,
+			ACPSessionID: inserted.ID,
+			ProjectIDs:   []uuid.UUID{ws.ProjectID},
+			ExpiresIn:    s.cfg.SystemTokenTTL,
+		})
+		if err != nil {
+			return err
+		}
+		tokenRes = res
+		return nil
+	})
+	if txErr != nil {
 		s.releaseOnFailure(ctx, sess, sessCaller, worktreeID)
-		return nil, err
+		return nil, txErr
 	}
 
 	// 8. audit
@@ -215,11 +242,16 @@ func (s *sessionService) Create(ctx context.Context, c Caller, in CreateSessionI
 		"requirement_id": reqID,
 	})
 
-	// 9. async spawn（失败时回滚 worktree）
+	// 9. async spawn（失败时回滚 worktree + revoke MCP token）
+	extraEnv := map[string]string{
+		"ACW_MCP_TOKEN": tokenRes.Plaintext,
+		"ACW_MCP_URL":   s.cfg.MCPPublicURL,
+	}
 	go func() {
 		spawnCtx, cancel := context.WithTimeout(context.Background(), 60*time.Second)
 		defer cancel()
-		if _, err := s.sup.Spawn(spawnCtx, out, kind, nil); err != nil {
+		if _, err := s.sup.Spawn(spawnCtx, out, kind, extraEnv); err != nil {
+			_ = s.mcpTokens.RevokeBySession(spawnCtx, out.ID)
 			s.releaseOnFailure(spawnCtx, out, sessCaller, worktreeID)
 		}
 	}()