repl: peel trailing punctuation from @path mentions (#7 follow-up)

Natural-language prose like "look at @README.md, then..." or
"@foo.lua." at sentence end previously failed to expand because the
trailing comma/period was included in the path.

Now: if the raw token doesn't resolve, peel trailing chars from
[.,;:?!)] one at a time until the path resolves or no more peels are
possible. On success, the peeled chars are emitted verbatim AFTER the
closing fence so the original punctuation is preserved.

Surfaced during higgs smoke test (TC: "say the first line of
@README.md, then stop" — the trailing comma broke resolution).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

repl.lua

@@ -54,7 +54,22 @@ local function expand_mentions(line, on_status)
         local at_start = (i == 1) or line:sub(i - 1, i - 1):match("%s") ~= nil
         if at_start and line:sub(i, i) == "@" then
             local path_end = line:find("%s", i + 1) or (#line + 1)
-            local path = line:sub(i + 1, path_end - 1)
+            local raw = line:sub(i + 1, path_end - 1)
+            -- Peel one or more trailing punctuation chars (,.;:?!) if the
+            -- full path doesn't resolve — handles natural prose like
+            -- "look at @README.md, then..." or "@foo.lua." at sentence end.
+            local path, trail = raw, ""
+            while #path > 0 do
+                local f = io.open(path, "rb")
+                if f then f:close(); break end
+                local last = path:sub(-1)
+                if last:match("[%.,;:?!)]") then
+                    trail = last .. trail
+                    path  = path:sub(1, -2)
+                else
+                    break
+                end
+            end
             if path ~= "" then
                 local content, truncated = _read_truncated(path)
                 if content then
@@ -62,12 +77,12 @@ local function expand_mentions(line, on_status)
                         on_status(("@%s expanded (%d bytes%s)"):format(
                             path, #content, truncated and ", truncated" or ""))
                     end
-                    out[#out + 1] = ("```%s path=%s\n%s\n```"):format(
-                        _lang_of(path), path, content)
+                    out[#out + 1] = ("```%s path=%s\n%s\n```%s"):format(
+                        _lang_of(path), path, content, trail)
                     i = path_end
                 else
                     if on_status then
-                        on_status(("@%s: not found"):format(path))
+                        on_status(("@%s: not found"):format(raw))
                     end
                     out[#out + 1] = line:sub(i, path_end - 1)
                     i = path_end