fix(cli): --urls-file with a single row now works (#86)

A one-line --urls-file produced entries.len()==1, which the batch gates
(run_batch / run_batch_llm require >1) skipped, so control fell to the
single-scrape path — which reads cli.urls (empty) and errored 'no input
provided'. Two+ rows worked; exactly one did not.

Backfill the lone file URL into cli.urls before the gates so a one-line
file behaves identically to a positional URL (stdout, --output-dir, cloud
fallback, --raw-html, --diff, LLM paths). The comma/CSV url,filename parsing
is unchanged (verified irrelevant to this bug). Adds 3 network-free tests.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

crates/webclaw-cli/src/main.rs

@@ -864,6 +864,18 @@ fn collect_urls(cli: &Cli) -> Result<Vec<(String, Option<String>)>, String> {
     Ok(entries)
 }
 
+/// When `--urls-file` supplies exactly one URL and no positional URL was given,
+/// treat it like a single positional URL so a one-line file behaves identically
+/// to `webclaw <url>` (stdout, `--output-dir`, cloud fallback, `--raw-html`,
+/// `--diff`, LLM paths). Without this the lone file URL gives `entries.len() == 1`,
+/// which the batch gates skip, and the single path then finds an empty `cli.urls`
+/// and errors "no input provided". See issue #86.
+fn backfill_single_file_url(urls: &mut Vec<String>, entries: &[(String, Option<String>)]) {
+    if urls.is_empty() && entries.len() == 1 {
+        urls.push(entries[0].0.clone());
+    }
+}
+
 /// Result that can be either a local extraction or a cloud API JSON response.
 enum FetchOutput {
     Local(Box<ExtractionResult>),
@@ -2624,7 +2636,7 @@ async fn run_research(cli: &Cli, query: &str) -> Result<(), String> {
 async fn main() {
     dotenvy::dotenv().ok();
 
-    let cli = Cli::parse();
+    let mut cli = Cli::parse();
     init_logging(cli.verbose);
 
     // Subcommand path. Handled before the flag dispatch so a subcommand
@@ -2828,6 +2840,11 @@ async fn main() {
         }
     };
 
+    // A single URL sourced only from --urls-file must behave like a positional
+    // URL (issue #86): the batch gates below require len > 1, and the single
+    // path reads cli.urls, so a one-line file would otherwise hit "no input".
+    backfill_single_file_url(&mut cli.urls, &entries);
+
     // LLM modes: --extract-json, --extract-prompt, --summarize
     // When multiple URLs are provided, run batch LLM extraction over all of them.
     if has_llm_flags(&cli) {
@@ -2899,6 +2916,36 @@ mod tests {
     use super::*;
     use webclaw_core::Content;
 
+    // issue #86: a single URL sourced only from --urls-file must be promoted to
+    // a positional URL so it takes the single-scrape path (batch gates need >1).
+    #[test]
+    fn single_file_url_backfilled_into_positional() {
+        let mut urls: Vec<String> = Vec::new();
+        let entries = vec![("https://example.com".to_string(), None)];
+        backfill_single_file_url(&mut urls, &entries);
+        assert_eq!(urls, vec!["https://example.com".to_string()]);
+    }
+
+    #[test]
+    fn positional_urls_left_untouched() {
+        let mut urls = vec!["https://a.com".to_string()];
+        let entries = vec![("https://a.com".to_string(), None)];
+        backfill_single_file_url(&mut urls, &entries);
+        assert_eq!(urls, vec!["https://a.com".to_string()]);
+    }
+
+    #[test]
+    fn multiple_file_urls_not_backfilled() {
+        // 2+ URLs already route to run_batch, so cli.urls stays empty here.
+        let mut urls: Vec<String> = Vec::new();
+        let entries = vec![
+            ("https://a.com".to_string(), None),
+            ("https://b.com".to_string(), None),
+        ];
+        backfill_single_file_url(&mut urls, &entries);
+        assert!(urls.is_empty());
+    }
+
     fn empty_result(title: Option<&str>, url: Option<&str>, markdown: &str) -> ExtractionResult {
         ExtractionResult {
             metadata: Metadata {