test: drop redundant tests, make the vacuous ones real

Audit of all 205 tests (five read-only passes plus a line-by-line
re-check). Ten test functions were removed or merged and eight
subsumed assertion blocks trimmed; the suite is down to 180 tests with
no loss of mutation coverage, and four tests that were passing for
nothing now fail when the code they name is broken.

Redundant (deleted or merged):
- twitter: `syndication_text_only_has_no_media` (re-asserts its own
  empty fixture), `..._keeps_multibyte_text` (both transforms are
  no-ops for that text), `..._strips_trailing_short_link_without_entities`
  (same branch as `..._media_short_link`, which now also covers the
  real multibyte tweet), `..._regardless_of_index_units` (its
  `display_text_range` rationale outlived the function it described).
- pixiv: `test_fetch` (a bare `is_ok()` on the illustration
  `download_media_pixiv_original_with_referer` already asserts and
  downloads, and the only network touch in a plain `cargo test`),
  `startup_validation_only_disables_on_a_definitive_failure` (four rows
  that are a subset of the retry-policy table; the `validate()` branch
  it was named for is not asserted at all).
- bilibili: `from_item_legacy_draw_shape_still_parses` (its fixture is
  the same legacy `draw` shape `from_item_maps_draw_images_and_topic`
  builds, with a subset of its assertions).
- site/mod.rs: two `Ok(None)` cases merged into one test.
- urls.rs: `cache_hit_success_keeps_the_cache_entry` (the `/test` test
  asserts the same two things under stricter settings), plus a
  `assert_ne!` loop that re-states the mapping assertions above it.
- send/mod.rs: `media_group_success_and_forward_ok` (the forward half is
  covered by `post_send_forwards_immediately_when_configured`; the
  `is_ok()` half cannot see the returned file ids), and two boundary
  rows implied by the constant they sit next to.
- commands.rs: the parse tail that `every_documented_invocation_parses`
  already covers per README form, and three `debug_report` rows the
  escaping test pins with stronger input.

Passing for nothing (now real):
- `truncate_caption_does_not_split_an_html_entity` — the cut lands
  inside the entity, so `!contains("&amp")` never fired; it now asserts
  the exact output in both directions and fails when the guard in
  `truncate_caption` is deleted (verified).
- `pipeline_resizes_oversized_jpeg` — magic bytes and a non-empty buffer
  pass for a copy-through; it now decodes the output's headers and
  fails when the JPEG branch skips the resize (verified).
- `live_validate_with_bogus_token_fails` — expected `PixivError::Api`,
  which the status check before the body read made unreachable; a bogus
  token is a 4xx. Confirmed against the live endpoint: the old
  assertion fails with `got Err(Status(400))`, the new one passes.
- bsky `live_fetch_with_photos` — its URL is a text-only post and it had
  a byte-identical twin, so no live test pinned media; it now points at a
  labelled post with photos and asserts media + the label (live-verified).

Also fixed, found by turning the runtime-sweep test into a real one:
the 30 s lease-expiry sweep recovered crashed rows but never woke a
worker, so a recovered task waited for the next unrelated enqueue (every
worker is parked on `notify` when no row is pending). `recover_update`
now reports its count, `recover_expired` wakes a worker when it changed
something, and `runtime_sweep_recovers_expired_lease` drives the spawned
loop with a paused clock instead of calling the recovery by hand — it
fails on both the missing wake-up and a sweep that recovers nothing.

Verified: `cargo fmt --check`, `cargo clippy --workspace --all-targets
--locked -- -D warnings`, `cargo test --workspace --locked` (180 passed,
14 ignored) and `cargo test -p x-media -- --ignored live` (13 passed).

crates/x-media/src/site/mod.rs

@@ -778,13 +778,25 @@ mod tests {
 
     #[test]
     fn truncate_caption_does_not_split_an_html_entity() {
-        // An entity crossing the cut must not be left half-open (&amp without ;).
-        let mut long = "a".repeat(MAX_CAPTION_CHARS - 4);
-        long.push_str("&bbbb");
-        let out = truncate_caption(&long);
-        assert!(out.chars().count() <= MAX_CAPTION_CHARS);
-        assert!(!out.contains("&amp"), "half entity left: {out:?}");
-        assert!(!out.ends_with('&'));
+        // The exact output is what pins the guard: a cut that keeps `&am` (no
+        // `;`) leaves a half-open entity that `!contains("&amp")` cannot see,
+        // so the old assertions stayed green with the guard deleted. Both
+        // directions matter — an entity the cut falls inside is dropped whole,
+        // one the cut falls after is kept whole.
+        for (long, expected) in [
+            (
+                "a".repeat(MAX_CAPTION_CHARS - 4) + "&amp;bbbb",
+                "a".repeat(MAX_CAPTION_CHARS - 4) + "…",
+            ),
+            (
+                "a".repeat(MAX_CAPTION_CHARS - 6) + "&amp;bbbb",
+                "a".repeat(MAX_CAPTION_CHARS - 6) + "&amp;…",
+            ),
+        ] {
+            let out = truncate_caption(&long);
+            assert_eq!(out, expected);
+            assert!(out.chars().count() <= MAX_CAPTION_CHARS, "{out:?}");
+        }
     }
 
     #[test]
@@ -796,15 +808,15 @@ mod tests {
     }
 
     #[tokio::test]
-    async fn unsupported_url_returns_none() {
-        let result = fetch("https://example.com/some/article").await;
-        assert!(matches!(result, Ok(None)), "got {result:?}");
-    }
-
-    #[tokio::test]
-    async fn unknown_scheme_returns_none() {
-        let result = fetch("not a url at all").await;
-        assert!(matches!(result, Ok(None)), "got {result:?}");
+    async fn unsupported_urls_return_none() {
+        // Neither a URL no site pattern matches nor a string that is no URL at
+        // all is an error: both answer `Ok(None)`, which is what keeps the bot
+        // silent on links it cannot handle (only a registered-but-disabled site
+        // gets a reply).
+        for url in ["https://example.com/some/article", "not a url at all"] {
+            let result = fetch(url).await;
+            assert!(matches!(result, Ok(None)), "{url}: got {result:?}");
+        }
     }
 
     #[test]