feat(core): SearchOpts domain type for budget controls (fb-34)

3 optional knobs (max_tokens, snippet_chars, cursor); Default = all
None = no enforcement (backwards-compat existing search behavior).

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

crates/kebab-core/src/lib.rs

@@ -51,7 +51,7 @@ pub use metadata::{
 };
 pub use search::{
     DocFilter, DocSummary, RetrievalDetail, SearchFilters, SearchHit,
-    SearchMode, SearchQuery,
+    SearchMode, SearchOpts, SearchQuery,
 };
 pub use answer::{
     Answer, AnswerCitation, AnswerRetrievalSummary, ModelRef, RefusalReason, TokenUsage,

crates/kebab-core/src/search.rs

@@ -96,6 +96,18 @@ pub struct DocSummary {
     pub chunker_version: ChunkerVersion,
 }
 
+/// p9-fb-34: caller-supplied output budget knobs for `App::search_with_opts`.
+/// All `None` = no enforcement (existing behavior).
+#[derive(Clone, Debug, Default, PartialEq, Serialize, Deserialize)]
+pub struct SearchOpts {
+    /// chars/4 approximation of wire JSON token cost. None = no cap.
+    pub max_tokens: Option<usize>,
+    /// Per-hit snippet character cap. None = use config default.
+    pub snippet_chars: Option<usize>,
+    /// Opaque base64 cursor from a previous response. None = first page.
+    pub cursor: Option<String>,
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -135,4 +147,12 @@ mod tests {
         assert_eq!(v["indexed_at"], "2026-05-09T12:00:00Z");
         assert_eq!(v["stale"], true);
     }
+
+    #[test]
+    fn search_opts_default_is_all_none() {
+        let opts = SearchOpts::default();
+        assert!(opts.max_tokens.is_none());
+        assert!(opts.snippet_chars.is_none());
+        assert!(opts.cursor.is_none());
+    }
 }