fix(rewrite): reserve canonical-URL headroom for short-form platforms

src/crier/cli.py

@@ -860,7 +860,7 @@ def publish(file: str, platform_args: tuple[str, ...], profile_name: str | None,
             else:
                 platform_cls = get_platform(platform_name)
                 platform = platform_cls(api_key or "dry-run")
-                max_len = platform.max_content_length
+                max_len = platform.rewrite_max_length(article)
 
                 # Check if auto-rewrite would be triggered
                 if auto_rewrite and llm_provider and max_len and len(article.body) > max_len:
@@ -1052,7 +1052,7 @@ def publish(file: str, platform_args: tuple[str, ...], profile_name: str | None,
                 platform_rewrite_content = None
 
                 if auto_rewrite and llm_provider and platform.max_content_length:
-                    max_len = platform.max_content_length
+                    max_len = platform.rewrite_max_length(article)
                     if len(article.body) > max_len:
                         from .rewrite import auto_rewrite_for_platform
 
@@ -3168,7 +3168,7 @@ def get_display_path(fp: Path) -> str:
                 platform_cls = get_platform(platform)
                 plat = platform_cls(api_key)
                 publish_article = article
-                max_len = platform_cls.max_content_length
+                max_len = plat.rewrite_max_length(article)
                 rewritten = False
                 rewrite_content = None
 
@@ -4299,7 +4299,7 @@ def schedule_run(dry_run: bool, json_output: bool):
                     )
 
                 platform_cls = get_platform(platform_name)
-                max_len = platform_cls(api_key).max_content_length
+                max_len = platform_cls(api_key).rewrite_max_length(article)
                 if max_len and len(article.body) > max_len:
                     retry = (
                         post.auto_rewrite_retry

src/crier/platforms/base.py

@@ -96,6 +96,9 @@ class Platform(ABC):
     supports_threads: bool = False
     # Maximum number of posts in a thread (if supports_threads)
     thread_max_posts: int = 25
+    #: Short-form platforms append the canonical URL to rewritten posts
+    #: (see ``_append_canonical_url``). Auto-rewrites must reserve room for it.
+    appends_canonical_url: bool = False
     # Request timeout in seconds
     timeout: int = 30
     # Max retries for transient failures (429, 502, 503, 504, ConnectionError)
@@ -119,6 +122,34 @@ def format_for_manual(self, article: Article) -> str:
         """
         return article.body
 
+    def rewrite_max_length(self, article: Article) -> int | None:
+        """Return the max output length for an auto-rewrite of ``article``.
+
+        Short-form platforms append the canonical URL to rewritten content
+        (see ``_append_canonical_url``). If the LLM is told to write up to
+        ``max_content_length`` characters and the URL is appended afterwards,
+        the final post exceeds the platform limit and the content-length check
+        fails. Returning a reduced budget lets the rewrite leave room for the
+        URL.
+
+        Subclasses that append the URL should set ``appends_canonical_url``.
+        Returns ``None`` when the platform has no character limit.
+        """
+        if self.max_content_length is None:
+            return None
+
+        budget = self.max_content_length
+        if (
+            self.appends_canonical_url
+            and article.canonical_url
+            and article.canonical_url not in (article.body or "")
+        ):
+            # Reserve room for the "\n\n" separator plus the URL itself.
+            budget -= len(article.canonical_url) + 2
+
+        # Guard against limits smaller than a canonical URL.
+        return max(budget, 1)
+
     def _check_content_length(self, content: str) -> str | None:
         """Check if content exceeds platform limit.
 

src/crier/platforms/bluesky.py

@@ -99,6 +99,7 @@ class Bluesky(Platform):
     base_url = "https://bsky.social/xrpc"
     max_content_length = 300  # Bluesky character limit
     is_short_form = True
+    appends_canonical_url = True
     api_key_url = "https://bsky.app/settings/app-passwords"
     supports_threads = True
     supports_stats = True

src/crier/platforms/linkedin.py

@@ -25,6 +25,7 @@ class LinkedIn(Platform):
     base_url = "https://api.linkedin.com/v2"
     compose_url = "https://www.linkedin.com/feed/?shareActive=true"
     max_content_length = 3000
+    appends_canonical_url = True
     supports_stats = True
     api_key_url = None  # Requires OAuth app setup
 

src/crier/platforms/mastodon.py

@@ -28,3 +28,4 @@ class Mastodon(FediversePlatform):
     description = "Short posts (500 chars)"
     max_content_length = 500
     default_instance = "mastodon.social"
+    appends_canonical_url = True

src/crier/platforms/threads.py

@@ -26,6 +26,7 @@ class Threads(Platform):
     base_url = "https://graph.threads.net/v1.0"
     max_content_length = 500  # Threads character limit
     is_short_form = True
+    appends_canonical_url = True
     api_key_url = "https://developers.facebook.com/"
     supports_delete = False
     supports_stats = True

src/crier/platforms/twitter.py

@@ -22,6 +22,7 @@ class Twitter(Platform):
     description = "Short posts (280 chars, manual)"
     max_content_length = 280  # Twitter character limit
     is_short_form = True
+    appends_canonical_url = True
     compose_url = "https://twitter.com/compose/tweet"
     api_key_url = None  # Manual mode only
     supports_delete = False

src/crier/publishing.py

@@ -113,7 +113,7 @@ def prepare_publish(
         posted_content = rewrite_content
     elif auto_rewrite and llm_provider:
         platform_obj = get_platform(platform)(api_key)
-        max_len = platform_obj.max_content_length
+        max_len = platform_obj.rewrite_max_length(article)
         if max_len and len(article.body) > max_len:
             rw = auto_rewrite_for_platform(
                 article, platform, max_len, llm_provider,

tests/test_platforms.py

@@ -142,6 +142,88 @@ def test_check_content_length_exceeds_limit(self):
         assert "280" in error
 
 
+class TestRewriteMaxLength:
+    """Tests for Platform.rewrite_max_length URL headroom logic."""
+
+    def test_no_limit_returns_none(self, sample_article):
+        """Platforms without a character limit have no rewrite budget."""
+        platform = DevTo("k")
+        assert platform.max_content_length is None
+        assert platform.rewrite_max_length(sample_article) is None
+
+    def test_non_appending_platform_full_budget(self):
+        """Platforms that don't append the URL keep the full limit."""
+        platform = DevTo("k")  # long-form, appends_canonical_url=False
+        # DevTo has no limit; use a hypothetical limited non-appender instead
+        class Limited(Platform):
+            name = "limited"
+            max_content_length = 300
+
+            def publish(self, article): ...
+            def update(self, article_id, article): ...
+            def list_articles(self, limit=10): ...
+            def get_article(self, article_id): ...
+
+        p = Limited("k")
+        assert p.appends_canonical_url is False
+        article = Article(title="t", body="x",
+                          canonical_url="https://example.com/a")
+        assert p.rewrite_max_length(article) == 300
+
+    def test_appending_platform_reserves_url_room(self):
+        """Budget subtracts canonical URL + separator for URL-appenders."""
+        platform = Bluesky("handle:pw")
+        url = "https://example.com/blog/some-post"
+        article = Article(title="t", body="x", canonical_url=url)
+        budget = platform.rewrite_max_length(article)
+        assert budget == 300 - len(url) - 2
+        # Final post (budget + separator + URL) fits exactly within the limit.
+        assert budget + len(url) + 2 <= platform.max_content_length
+
+    def test_appending_platform_no_url_full_budget(self):
+        """Without a canonical URL nothing is reserved."""
+        platform = Bluesky("handle:pw")
+        assert platform.rewrite_max_length(
+            Article(title="t", body="x", canonical_url=None)
+        ) == 300
+
+    def test_url_already_in_body_not_double_counted(self):
+        """A rewrite that already contains the URL isn't penalised."""
+        platform = Bluesky("handle:pw")
+        url = "https://example.com/blog/some-post"
+        article = Article(title="t", body="x " + url, canonical_url=url)
+        assert platform.rewrite_max_length(article) == 300
+
+    def test_limit_smaller_than_url_floored_at_one(self):
+        """Even a tiny limit never yields a non-positive budget."""
+        class Tiny(Platform):
+            name = "tiny"
+            max_content_length = 5
+            appends_canonical_url = True
+
+            def publish(self, article): ...
+            def update(self, article_id, article): ...
+            def list_articles(self, limit=10): ...
+            def get_article(self, article_id): ...
+
+        p = Tiny("k")
+        url = "https://example.com/a-very-long-canonical-url"
+        assert p.rewrite_max_length(
+            Article(title="t", body="x", canonical_url=url)
+        ) == 1
+
+    @pytest.mark.parametrize("platform_cls", [Bluesky, Twitter, Mastodon])
+    def test_short_form_url_appenders_flag_set(self, platform_cls):
+        """URL-appending short-form platforms opt into the headroom logic."""
+        p = platform_cls("k")
+        assert p.appends_canonical_url is True
+
+    def test_threads_appends_canonical_url(self):
+        """Threads (user_id:token key) opts into the headroom logic too."""
+        p = Threads("12345:token")
+        assert p.appends_canonical_url is True
+
+
 class TestTwitterManualMode:
     """Tests for Twitter manual mode platform."""
 

tests/test_publishing.py

@@ -123,6 +123,7 @@ def test_prepare_publish_auto_rewrite_success(mode, key, parse, get_plat, auto_r
 
     inst = MagicMock()
     inst.max_content_length = 300
+    inst.rewrite_max_length.return_value = 300
     get_plat.return_value = lambda _k: inst
 
     llm_provider = MagicMock()
@@ -156,6 +157,7 @@ def test_publish_one_auto_rewrite_failure(mode, key, parse, get_plat, auto_rw):
 
     inst = MagicMock()
     inst.max_content_length = 300
+    inst.rewrite_max_length.return_value = 300
     get_plat.return_value = lambda _k: inst
 
     llm_provider = MagicMock()