Mount dials its peer at once and fails if none answers; a peer out of reach is said as `dial failed: <reason>`

Mount took any well-formed dial and nothing was found out until the
first look through it, which then said `look: look: dial`. Mount now
probes the peer (version, attach, its root) with the turn out, and fails
its write, mounting nothing, when none answers; the dial errors read as
words, `no answer`, `timed out`, `hung up`, and a look through a peer
gone since names its path: `look: /n/peer/f: dial failed: no answer`.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

1 files changed, 15 insertions, 0 deletions

diff --git a/src/builtins.zig b/src/builtins.zig
index 404e78f4..3f4a680c 100644
--- a/src/builtins.zig
+++ b/src/builtins.zig
@@ -676,6 +676,21 @@ pub const Mount = struct {
         const dial = std.mem.trim(u8, args.rest(), " \t");
         if (dial.len == 0) return c.p.reportError(c.id, "Mount name dial", error.MissingArgument);
         c.p.fs.mount(c.p.gpa, name, dial) catch |err| return c.p.reportError(c.id, "Mount", err);
+        // A mount that cannot be reached is said now, and taken back, not
+        // found out by the first look through it.
+        const reached = reached: {
+            pardes.turn.yield();
+            defer pardes.turn.back();
+            break :reached @import("9p_io.zig").Client.probe(c.p.gpa, dial);
+        };
+        reached catch |err| {
+            if (c.p.fs.mounts.pop()) |gone| {
+                c.p.gpa.free(gone.name);
+                c.p.gpa.free(gone.dial);
+            }
+            var what: [160]u8 = undefined;
+            return c.p.reportError(c.id, std.fmt.bufPrint(&what, "Mount {s} {s}", .{ name, dial[0..@min(dial.len, 100)] }) catch "Mount", err);
+        };
     }
 };