fix: M6.41批 — 启动失败原因透传 + 阅读器左缘返回/阅读页接入view栈 + 后台管理按钮点不动 + 阅读器瘦身(fonts common+页位图释放) + files txt换行

- launcher(453): app_launcher.c g_launch_fail_reason+launch_fail()统一出口(5失败点 fork OOM/exec/no such file/missing dep/execpipe)+main_menu.c launch_fail_toast(缺依赖/CANNOT START: name(reason))+toast256
- launcher(457): bg_page.c bgm_enumerate跳过term_at_ms(杀后当下消失)+不可杀行按钮置灰+row_tap/top_action返回1; subpage.c 消warning
- reader(454): reader_on_swipe LEFT/RIGHT→返回(先关overlay否则page_pop回书架)+app.c书架根LEFT→exit
- reader(458瘦身A+B): app.json fonts full→common(省13MB atlas)+reader.c RD_PAGE_CACHE 3→2+g_anim_old懒分配/anim_done释放+on_enter/on_leave页位图离开释放重建
- reader(459导航): reader_open返回int+shelf点书push ACT_READER(阅读页接入view栈,on_enter/on_leave驱动) — 使454左缘返回+458瘦身B真正生效
- files(455): viewer.c viewer_cp_len+按码位折行(txt中文不冲出右缘)

0warning;宿主测试全过;files二进制已热更

patch_v2/meow_launcherd/app_launcher.c

@@ -23,6 +23,28 @@ static void app_name_copy(char *dst, int cap, const char *src)
 }
 
 
+/* M6.40 启动失败原因透传：launch_app/launch_activity（→launch_app_chain）返回 -1 前按实际
+ * 失败点填具体原因（fork OOM / exec 失败 / 缺依赖 / 路径不存在等），供 main_menu.c 的
+ * launch_fail_toast 显示「CANNOT START: %s（%s）」；success 路径恒为 ""。 */
+static char g_launch_fail_reason[160] = "";
+
+const char *launch_fail_reason(void)
+{
+    return g_launch_fail_reason;
+}
+
+/* 内部失败出口：设原因 + 记统一失败日志 + 返回 -1（各失败分支复用）。 */
+static int launch_fail(struct app *a, const char *fmt, ...)
+{
+    va_list ap;
+    va_start(ap, fmt);
+    vsnprintf(g_launch_fail_reason, sizeof g_launch_fail_reason, fmt, ap);
+    va_end(ap);
+    logmsg("launch failed: %s reason=%s", a->name, g_launch_fail_reason);
+    return -1;
+}
+
+
 /* ---- amsd 上报 / 控制挂点（AMSD_DESIGN §4）：best-effort，amsd 不在不影响 launcher ---- */
 #define MEOW_AMS_SOCK_DEFAULT "/usr/data/meow_ams.sock"
 
@@ -1585,8 +1607,9 @@ static int launch_app_chain(struct app *a, const char *chain)
     uint32_t pick_req = 0;
     meow_ams_take_picker(pick_action, sizeof pick_action,
                          pick_caller, sizeof pick_caller, &pick_req);
-    if (!a->ok) { logmsg("launch blocked: exec not ok"); return -1; }
     meow_dep_clear_reason();   /* 每次 launch 入口清 stale 依赖阻断原因（防上一 app 残留） */
+    g_launch_fail_reason[0] = 0;   /* M6.40：同上，清 stale 启动失败原因 */
+    if (!a->ok) { logmsg("launch blocked: exec not ok"); return launch_fail(a, "no such file: %s", a->exec); }
 
     /* M4 后台保活恢复：该 App 驻留后台（播放中经 nav-exit 转过）→ 原进程回前台，
      * 不 fork/exec（进程仍存无法注入新 env：chain/picker 上下文忽略，记日志）。
@@ -1613,7 +1636,7 @@ static int launch_app_chain(struct app *a, const char *chain)
         char dep_missing[32] = "";
         if (meow_check_app_depends(a, dep_missing, sizeof dep_missing) != 0) {
             logmsg("launch blocked: dep '%s' missing (CANNOT START: %s)", dep_missing, a->name);
-            return -1;
+            return launch_fail(a, "missing dep: %s", dep_missing);
         }
     }
     /* 冷启动：标记内容置为前台归属（a->id），让本 App 首帧即不被自抑（后台常驻 App 继续自抑）。
@@ -1641,7 +1664,7 @@ static int launch_app_chain(struct app *a, const char *chain)
      * watchdog and waitpid — so an exec failure never leaves an orphan watchdog
      * and never masquerades as "app ran and exited". */
     int execpipe[2];
-    if (pipe(execpipe) < 0) { logmsg("exec pipe failed: %s", strerror(errno)); return -1; }
+    if (pipe(execpipe) < 0) { logmsg("exec pipe failed: %s", strerror(errno)); return launch_fail(a, "exec pipe failed: %s", strerror(errno)); }
     fcntl(execpipe[1], F_SETFD, FD_CLOEXEC);
 
     /* AMSD_DESIGN §5：stdout/stderr 管道捕获（logcat 思路）。fork 前建管道；子进程 dup2 到
@@ -1661,7 +1684,7 @@ static int launch_app_chain(struct app *a, const char *chain)
         close(execpipe[0]); close(execpipe[1]);
         if (out_pipe[0] >= 0) close(out_pipe[0]);
         if (out_pipe[1] >= 0) close(out_pipe[1]);
-        logmsg("fork failed: %s", strerror(errno)); return -1;
+        logmsg("fork failed: %s", strerror(errno)); return launch_fail(a, "fork failed: %s", strerror(errno));
     }
     if (pid == 0) {
         /* child: exec the app. M2.12 注入 MEOW_LOG_DIR + MEOW_DATA_DIR/MEOW_CACHE_DIR
@@ -1850,7 +1873,7 @@ static int launch_app_chain(struct app *a, const char *chain)
         int st = 0;
         reap_wait(pid, &st);   /* reap the failed child（有界） */
         if (out_fd >= 0) close(out_fd);
-        return -1;
+        return launch_fail(a, "exec failed: %s (errno %d)", strerror(exe_err), exe_err);
     }
     }   /* end if (!resumed)：冷启动分支（prepare/fork/exec/确认） */