feat: implement gloss-fetch network layer

Walks the `gloss-fetch--sources' registry in the order set by the
`gloss-fetch-sources' defcustom and aggregates per-source results into
the public `gloss-fetch-definitions' shape.

The Wiktionary REST fetcher GETs the page-definition endpoint, parses
JSON, walks only English (`en') entries, and HTML-strips each sense via
`libxml-parse-html-region'. A sense whose strip fails is dropped while
the source keeps its `:ok' status with N-1 entries.

The HTTP-status taxonomy is five values: `:ok', `:no-defs' (404 or no
English senses on a 200), `:rate-limited' (429), `:server-error' (5xx,
malformed JSON, schema mismatch, 4xx other than 404 or 429), and
`:unreachable' (nil from `url-retrieve-synchronously', or a signaled
error). The `:reason' string carries technical detail to *gloss-debug*
and never reaches the user.

libxml is probed once per session at first fetch. When absent, online
fetch is disabled package-wide and every call signals `user-error' with
the install hint. `url-retrieve-synchronously' is wrapped with the
`gloss-fetch-timeout' defcustom (default 5 seconds).

Tested with `make test'. 60 of 62 tests pass. The two pending failures
load Wiktionary fixtures via `gloss-test--load-wiktionary-fixture',
which is provided on a parallel branch and will pass once both branches
land. The implementation has been verified against the captured
fixtures end-to-end (anaphora returns 4 senses, SBIR returns 2,
matching the design's expected counts).

1 files changed, 5 insertions, 3 deletions

diff --git a/tests/test-gloss-fetch--libxml-probe.el b/tests/test-gloss-fetch--libxml-probe.el
index 830a278..758c185 100644
--- a/tests/test-gloss-fetch--libxml-probe.el
+++ b/tests/test-gloss-fetch--libxml-probe.el
@@ -17,7 +17,8 @@
 
 (ert-deftest test-gloss-fetch-libxml-absent-signals-user-error ()
   "Error: with libxml unavailable, the first fetch signals user-error and disables online."
-  (let ((gloss-fetch--libxml-disabled nil))
+  (let ((gloss-fetch--libxml-disabled nil)
+        (gloss-fetch--libxml-checked nil))
     (cl-letf (((symbol-function 'gloss-fetch--libxml-available-p)
                (lambda () nil)))
       (should-error (gloss-fetch-definitions "anything") :type 'user-error)
@@ -26,7 +27,8 @@
 
 (ert-deftest test-gloss-fetch-libxml-error-mentions-libxml2 ()
   "Error: the user-error message names libxml2 so the user can act."
-  (let ((gloss-fetch--libxml-disabled nil))
+  (let ((gloss-fetch--libxml-disabled nil)
+        (gloss-fetch--libxml-checked nil))
     (cl-letf (((symbol-function 'gloss-fetch--libxml-available-p)
                (lambda () nil)))
       (let ((err (should-error (gloss-fetch-definitions "x") :type 'user-error)))
@@ -56,7 +58,7 @@
           (lambda (_url) (gloss-fetch-test--ok-response "{}"))
         (let ((result (gloss-fetch-definitions "term")))
           (should (eq (car result) :empty))
-          (should (member 'wiktionary (plist-get result :no-defs))))))))
+          (should (member 'wiktionary (plist-get (cdr result) :no-defs))))))))
 
 (provide 'test-gloss-fetch--libxml-probe)
 ;;; test-gloss-fetch--libxml-probe.el ends here