add unreachable_pub lint, fix all 17 violations

pub → pub(crate) for SseReader methods (used across child modules).
pub → pub(super) for openai::stream_events, tool definitions, store
helpers. pub → private for normalize_link and differentiate_hub_with_graph
(only used within their own files).

Co-Authored-By: Proof of Concept <poc@bcachefs.org>

src/hippocampus/store/parse.rs

@@ -23,7 +23,7 @@ pub struct MemoryUnit {
     pub source_ref: Option<String>,
 }
 
-pub fn classify_filename(filename: &str) -> NodeType {
+pub(super) fn classify_filename(filename: &str) -> NodeType {
     let bare = filename.strip_suffix(".md").unwrap_or(filename);
     if bare.starts_with("daily-") { NodeType::EpisodicDaily }
     else if bare.starts_with("weekly-") { NodeType::EpisodicWeekly }
@@ -147,7 +147,7 @@ fn extract_md_links(content: &str, re: &Regex, source_file: &str) -> Vec<String>
         .collect()
 }
 
-pub fn normalize_link(target: &str, source_file: &str) -> String {
+fn normalize_link(target: &str, source_file: &str) -> String {
     let source_bare = source_file.strip_suffix(".md").unwrap_or(source_file);
 
     if target.starts_with('#') {

src/hippocampus/store/types.rs

@@ -434,7 +434,7 @@ pub struct GapRecord {
 }
 
 /// Per-node agent visit index: node_key → (agent_type → last_visit_timestamp)
-pub type VisitIndex = HashMap<String, HashMap<String, i64>>;
+pub(super) type VisitIndex = HashMap<String, HashMap<String, i64>>;
 
 // The full in-memory store
 #[derive(Default, Serialize, Deserialize)]
@@ -557,7 +557,7 @@ capnp_message!(AgentVisit,
     skip: [],
 );
 
-pub fn new_visit(node_uuid: [u8; 16], node_key: &str, agent: &str, outcome: &str) -> AgentVisit {
+pub(super) fn new_visit(node_uuid: [u8; 16], node_key: &str, agent: &str, outcome: &str) -> AgentVisit {
     AgentVisit {
         node_uuid,
         node_key: node_key.to_string(),
@@ -588,7 +588,7 @@ capnp_message!(TranscriptSegment,
     skip: [],
 );
 
-pub fn new_transcript_segment(transcript_id: &str, segment_index: u32, agent: &str) -> TranscriptSegment {
+pub(super) fn new_transcript_segment(transcript_id: &str, segment_index: u32, agent: &str) -> TranscriptSegment {
     TranscriptSegment {
         transcript_id: transcript_id.to_string(),
         segment_index,