L2: permission mode propagation across forward/calendar/adopt + PUT endpoint + tests

P1 - forward inherits mode:
- doForward: when creating a new target session, use InheritedMode from
  the source session (plan parent → plan child, cannot escalate)
- enforcement snapshot set from receiving agent

P1 - calendar_events gets permission_mode column:
- Added to 3 migration sites (sqlite init, pg init, incremental alter)
- CalendarEvent model gains PermissionMode field
- CreateCalendarEvent / UpdateCalendarEvent normalize + persist the field
- resolveCalendarSession: on new session → write event's mode;
  on reuse → ModeAtMost(cur, eventMode), prevents escalation
  (plan Agent's reminder fires into a workspace session = bypass)
- SendCalendarMail now takes permMode and threads it through
- fireEvent passes event.PermissionMode to all delivery paths

P1 - AdoptPlatformSession explicitly writes default mode:
- Writes DefaultPermissionMode + enforcement on adopt, instead of
  relying on DB column default (avoids silent drift on schema changes)

P2 - PUT /sessions/{id}/permission endpoint:
- New handler UpdateSessionPermission (auth required, access check)
- Registers PUT route alongside existing budget/alias endpoints
- Broadcasts session_update on change
- Does NOT refresh enforcement (design: snapshot at creation)

P3 - Tests (24 new cases):
- permission_mode_test.go: InheritedMode (6 cases), SetSessionPermissionMode
  roundtrip, dirty value fail-closed, NormalizePermissionMode, calendar event
  roundtrip/dirty/update, adopt writes default mode, plan escalation guard,
  3-level inheritance chain
- defaultsession_test.go: budget regression, permission mode regression
  (pins created=false → no reset on reuse)

Deploys with: bash deploy/redeploy-gateway.sh --skip-tests
Schema migration: auto via addMissingColumns (new column default 'workspace')

gateway/internal/db/migrate.go

@@ -84,10 +84,17 @@ var sqliteAddColumns = []struct{ table, column, ddl string }{
 	// to_address / agent_name，历史事件因此继续工作，不需要数据迁移。
 	{"calendar_events", "recipients", "ALTER TABLE calendar_events ADD COLUMN recipients TEXT NOT NULL DEFAULT '[]'"},
 	{"calendar_events", "delivery_mode", "ALTER TABLE calendar_events ADD COLUMN delivery_mode TEXT NOT NULL DEFAULT 'separate'"},
-	// 日历事件已触发的 occurrence。旧库为 NULL：等价于「从未触发」，
+	// 日历事件已触发的 occurrence。旧库为 NULL：等价于「从未触发」,
 	// 于是已过期的一次性事件会补发一次提醒 —— 这是可接受的，
 	// 而反过来（默认成 event_time）会让正在等的提醒永远发不出去。
 	{"calendar_events", "fired_for", "ALTER TABLE calendar_events ADD COLUMN fired_for DATETIME"},
+	// 日历事件的权限档位（plan / workspace / full）。事件触发时若新建会话，
+	// 用这一列定死档位；复用已有会话则取「会话现档 与 事件档」中更严那个。
+	//
+	// 旧库默认 'workspace'：历史事件补发提醒不该静默升到 full（提权路径
+	// 会被 P1 calendar 投递接线堵住，但这里默认值也得守住）。
+	// 与 sessions.permission_mode 的默认取向一致。
+	{"calendar_events", "permission_mode", "ALTER TABLE calendar_events ADD COLUMN permission_mode TEXT NOT NULL DEFAULT 'workspace'"},
 	// 本侧会话接管的平台会话 id。旧库默认空串 = 「不是接管来的」，
 	// 与新建会话的语义一致，不需要数据迁移。
 	{"sessions", "platform_id", "ALTER TABLE sessions ADD COLUMN platform_id TEXT NOT NULL DEFAULT ''"},

gateway/internal/db/migrations/init.sql

@@ -395,6 +395,8 @@ CREATE TABLE IF NOT EXISTS calendar_events (
     last_fired_at  TIMESTAMPTZ,
     -- 已触发的 occurrence（= 当时的 event_time）。见 init_sqlite.sql 的说明。
     fired_for      TIMESTAMPTZ,
+    -- 权限档位（plan / workspace / full）。见 init_sqlite.sql 的说明。
+    permission_mode TEXT NOT NULL DEFAULT 'workspace',
     created_at     TIMESTAMPTZ DEFAULT NOW(),
     updated_at     TIMESTAMPTZ DEFAULT NOW(),
     created_by     VARCHAR(128) NOT NULL DEFAULT ''

gateway/internal/db/migrations/init_sqlite.sql

@@ -433,6 +433,10 @@ CREATE TABLE IF NOT EXISTS calendar_events (
     -- 按 occurrence 比相等则精确：AdvanceRecurrence 改了 event_time 就再触发，
     -- 没改就永不重发。
     fired_for      DATETIME,
+    -- 权限档位（plan / workspace / full）。事件触发时新建会话 → 用此档位定死；
+    -- 复用已有会话 → 取「会话现档 与 事件档」中更严那个（ModeAtMost），
+    -- 不允许通过重复事件提权（plan 档 Agent 建的日程触发时拿 workspace 就绕开了 plan）。
+    permission_mode TEXT NOT NULL DEFAULT 'workspace',
     created_at     DATETIME DEFAULT (strftime('%Y-%m-%d %H:%M:%f','now')),
     updated_at     DATETIME DEFAULT (strftime('%Y-%m-%d %H:%M:%f','now')),