feat(core): FetchQuery / FetchOpts / FetchResult / FetchKind (fb-35)

Domain types for `kebab fetch` 3 modes (chunk / doc / span). All
types Serialize so wire layers hand them through serde_json
directly. FetchKind is snake_case-renamed to match the wire
discriminator literal in fetch_result.v1.

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

crates/kebab-core/src/fetch.rs

@@ -0,0 +1,87 @@
+//! p9-fb-35 verbatim fetch domain types.
+//!
+//! Three modes (chunk / doc / span) carried by [`FetchQuery`]; one
+//! response shape ([`FetchResult`]) discriminated by [`FetchKind`].
+//! All types are `Serialize` so the CLI / MCP wire layers can hand
+//! them straight through `serde_json::to_value`.
+
+use serde::{Deserialize, Serialize};
+use time::OffsetDateTime;
+
+use crate::asset::WorkspacePath;
+use crate::chunk::Chunk;
+use crate::ids::{ChunkId, DocumentId};
+
+#[derive(Clone, Debug)]
+pub enum FetchQuery {
+    Chunk(ChunkId),
+    Doc(DocumentId),
+    Span {
+        doc_id: DocumentId,
+        line_start: u32,
+        line_end: u32,
+    },
+}
+
+#[derive(Clone, Debug, Default)]
+pub struct FetchOpts {
+    /// chunk mode only: ±N chunks. None = no surrounding context.
+    pub context: Option<u32>,
+    /// doc / span mode only: chars/4 budget. None = no cap.
+    pub max_tokens: Option<usize>,
+}
+
+#[derive(Clone, Copy, Debug, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(rename_all = "snake_case")]
+pub enum FetchKind {
+    Chunk,
+    Doc,
+    Span,
+}
+
+#[derive(Clone, Debug, Serialize, Deserialize)]
+pub struct FetchResult {
+    pub kind: FetchKind,
+    pub doc_id: DocumentId,
+    pub doc_path: WorkspacePath,
+    #[serde(with = "time::serde::rfc3339")]
+    pub indexed_at: OffsetDateTime,
+    pub stale: bool,
+    // chunk mode payloads
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub chunk: Option<Chunk>,
+    #[serde(skip_serializing_if = "Vec::is_empty", default)]
+    pub context_before: Vec<Chunk>,
+    #[serde(skip_serializing_if = "Vec::is_empty", default)]
+    pub context_after: Vec<Chunk>,
+    // doc / span payloads
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub text: Option<String>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub line_start: Option<u32>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub line_end: Option<u32>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub effective_end: Option<u32>,
+    pub truncated: bool,
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn fetch_opts_default_is_all_none() {
+        let o = FetchOpts::default();
+        assert!(o.context.is_none());
+        assert!(o.max_tokens.is_none());
+    }
+
+    #[test]
+    fn fetch_kind_serializes_snake_case() {
+        let v = serde_json::to_value(FetchKind::Chunk).unwrap();
+        assert_eq!(v, serde_json::json!("chunk"));
+        let v = serde_json::to_value(FetchKind::Span).unwrap();
+        assert_eq!(v, serde_json::json!("span"));
+    }
+}

crates/kebab-core/src/lib.rs

@@ -23,6 +23,7 @@ pub mod vector;
 pub mod errors;
 pub mod traits;
 pub mod normalize;
+pub mod fetch;
 
 // Re-export the most commonly used items at the crate root, mirroring the
 // public surface listed in the task spec.
@@ -68,3 +69,4 @@ pub use traits::{
     SourceScope, TokenChunk, VectorStore,
 };
 pub use normalize::{nfc, to_posix};
+pub use fetch::{FetchKind, FetchOpts, FetchQuery, FetchResult};