fix(explain): address review findings — N+1 queries, duplicate decisions, silent errors

1. fetch_open_threads: replace N+1 loop (2 queries per thread) with a
   single query using correlated subqueries for note_count and started_by.
2. extract_key_decisions: track consumed notes so the same note is not
   matched to multiple events, preventing duplicate decision entries.
3. build_timeline_excerpt_from_pipeline: log tracing::warn on seed/collect
   failures instead of silently returning empty timeline.

.beads/last-touched

@@ -1 +1 @@
-bd-2i3z
+bd-9lbr

src/app/errors.rs

@@ -7,6 +7,10 @@ struct FallbackErrorOutput {
 struct FallbackError {
     code: String,
     message: String,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    suggestion: Option<String>,
+    #[serde(skip_serializing_if = "Vec::is_empty")]
+    actions: Vec<String>,
 }
 
 fn handle_error(e: Box<dyn std::error::Error>, robot_mode: bool) -> ! {
@@ -20,6 +24,8 @@ fn handle_error(e: Box<dyn std::error::Error>, robot_mode: bool) -> ! {
                         error: FallbackError {
                             code: "INTERNAL_ERROR".to_string(),
                             message: gi_error.to_string(),
+                            suggestion: None,
+                            actions: Vec::new(),
                         },
                     };
                     serde_json::to_string(&fallback)
@@ -59,6 +65,8 @@ fn handle_error(e: Box<dyn std::error::Error>, robot_mode: bool) -> ! {
             error: FallbackError {
                 code: "INTERNAL_ERROR".to_string(),
                 message: e.to_string(),
+                suggestion: None,
+                actions: Vec::new(),
             },
         };
         eprintln!(

src/app/handlers.rs

@@ -735,7 +735,7 @@ async fn handle_init(
         }
 
         let project_paths: Vec<String> = projects_flag
-            .unwrap()
+            .expect("validated: checked for None at lines 714-721")
             .split(',')
             .map(|p| p.trim().to_string())
             .filter(|p| !p.is_empty())
@@ -743,8 +743,10 @@ async fn handle_init(
 
         let result = run_init(
             InitInputs {
-                gitlab_url: gitlab_url_flag.unwrap(),
-                token_env_var: token_env_var_flag.unwrap(),
+                gitlab_url: gitlab_url_flag
+                    .expect("validated: checked for None at lines 714-721"),
+                token_env_var: token_env_var_flag
+                    .expect("validated: checked for None at lines 714-721"),
                 project_paths,
                 default_project: default_project_flag.clone(),
             },

src/app/robot_docs.rs

@@ -316,6 +316,17 @@ fn handle_robot_docs(robot_mode: bool, brief: bool) -> Result<(), Box<dyn std::e
                 "meta": {"elapsed_ms": "int"}
             }
         },
+        "explain": {
+            "description": "Auto-generate a structured narrative of an issue or MR",
+            "flags": ["<entity_type: issues|mrs>", "<IID>", "-p/--project <path>", "--sections <comma-list>", "--no-timeline", "--max-decisions <N>", "--since <period>"],
+            "valid_sections": ["entity", "description", "key_decisions", "activity", "open_threads", "related", "timeline"],
+            "example": "lore --robot explain issues 42 --sections key_decisions,activity --since 30d",
+            "response_schema": {
+                "ok": "bool",
+                "data": {"entity": "{type:string, iid:int, title:string, state:string, author:string, assignees:[string], labels:[string], created_at:string, updated_at:string, url:string?, status_name:string?}", "description_excerpt": "string?", "key_decisions": "[{timestamp:string, actor:string, action:string, context_note:string}]?", "activity": "{state_changes:int, label_changes:int, notes:int, first_event:string?, last_event:string?}?", "open_threads": "[{discussion_id:string, started_by:string, started_at:string, note_count:int, last_note_at:string}]?", "related": "{closing_mrs:[{iid:int, title:string, state:string, web_url:string?}], related_issues:[{entity_type:string, iid:int, title:string?, reference_type:string}]}?", "timeline_excerpt": "[{timestamp:string, event_type:string, actor:string?, summary:string}]?"},
+                "meta": {"elapsed_ms": "int"}
+            }
+        },
         "notes": {
             "description": "List notes from discussions with rich filtering",
             "flags": ["--limit/-n <N>", "--author/-a <username>", "--note-type <type>", "--contains <text>", "--for-issue <iid>", "--for-mr <iid>", "-p/--project <path>", "--since <period>", "--until <period>", "--path <filepath>", "--resolution <any|unresolved|resolved>", "--sort <created|updated>", "--asc", "--include-system", "--note-id <id>", "--gitlab-note-id <id>", "--discussion-id <id>", "--fields <list|minimal>", "--open"],
@@ -449,7 +460,8 @@ fn handle_robot_docs(robot_mode: bool, brief: bool) -> Result<(), Box<dyn std::e
         "17": "Not found",
         "18": "Ambiguous match",
         "19": "Health check failed",
-        "20": "Config not found"
+        "20": "Config not found",
+        "21": "Embeddings not built"
     });
 
     let workflows = serde_json::json!({

src/cli/autocorrect.rs

@@ -209,6 +209,16 @@ const COMMAND_FLAGS: &[(&str, &[&str])] = &[
         ],
     ),
     ("drift", &["--threshold", "--project"]),
+    (
+        "explain",
+        &[
+            "--project",
+            "--sections",
+            "--no-timeline",
+            "--max-decisions",
+            "--since",
+        ],
+    ),
     (
         "notes",
         &[
@@ -388,6 +398,7 @@ const CANONICAL_SUBCOMMANDS: &[&str] = &[
     "file-history",
     "trace",
     "drift",
+    "explain",
     "related",
     "cron",
     "token",

src/cli/commands/mod.rs

@@ -5,6 +5,7 @@ pub mod cron;
 pub mod doctor;
 pub mod drift;
 pub mod embed;
+pub mod explain;
 pub mod file_history;
 pub mod generate_docs;
 pub mod ingest;
@@ -35,6 +36,7 @@ pub use cron::{
 pub use doctor::{DoctorChecks, print_doctor_results, run_doctor};
 pub use drift::{DriftResponse, print_drift_human, print_drift_json, run_drift};
 pub use embed::{print_embed, print_embed_json, run_embed};
+pub use explain::{handle_explain, print_explain, print_explain_json, run_explain};
 pub use file_history::{print_file_history, print_file_history_json, run_file_history};
 pub use generate_docs::{print_generate_docs, print_generate_docs_json, run_generate_docs};
 pub use ingest::{

src/cli/mod.rs

@@ -277,6 +277,44 @@ pub enum Commands {
     /// Trace why code was introduced: file -> MR -> issue -> discussion
     Trace(TraceArgs),
 
+    /// Auto-generate a structured narrative of an issue or MR
+    #[command(after_help = "\x1b[1mExamples:\x1b[0m
+  lore explain issues 42                  # Narrative for issue #42
+  lore explain mrs 99 -p group/repo       # Narrative for MR !99 in specific project
+  lore -J explain issues 42               # JSON output for automation
+  lore explain issues 42 --sections key_decisions,open_threads  # Specific sections only
+  lore explain issues 42 --since 30d      # Narrative scoped to last 30 days
+  lore explain issues 42 --no-timeline    # Skip timeline (faster)")]
+    Explain {
+        /// Entity type: "issues" or "mrs" (singular forms also accepted)
+        #[arg(value_parser = ["issues", "mrs", "issue", "mr"])]
+        entity_type: String,
+
+        /// Entity IID
+        iid: i64,
+
+        /// Scope to project (fuzzy match)
+        #[arg(short, long)]
+        project: Option<String>,
+
+        /// Select specific sections (comma-separated)
+        /// Valid: entity, description, key_decisions, activity, open_threads, related, timeline
+        #[arg(long, value_delimiter = ',', help_heading = "Output")]
+        sections: Option<Vec<String>>,
+
+        /// Skip timeline excerpt (faster execution)
+        #[arg(long, help_heading = "Output")]
+        no_timeline: bool,
+
+        /// Maximum key decisions to include
+        #[arg(long, default_value = "10", help_heading = "Output")]
+        max_decisions: usize,
+
+        /// Time scope for events/notes (e.g. 7d, 2w, 1m, or YYYY-MM-DD)
+        #[arg(long, help_heading = "Filters")]
+        since: Option<String>,
+    },
+
     /// Detect discussion divergence from original intent
     #[command(after_help = "\x1b[1mExamples:\x1b[0m
   lore drift issues 42                    # Check drift on issue #42

src/core/error.rs

@@ -28,8 +28,11 @@ pub enum ErrorCode {
     OllamaUnavailable,
     OllamaModelNotFound,
     EmbeddingFailed,
+    EmbeddingsNotBuilt,
     NotFound,
     Ambiguous,
+    HealthCheckFailed,
+    UsageError,
     SurgicalPreflightFailed,
 }
 
@@ -52,8 +55,11 @@ impl std::fmt::Display for ErrorCode {
             Self::OllamaUnavailable => "OLLAMA_UNAVAILABLE",
             Self::OllamaModelNotFound => "OLLAMA_MODEL_NOT_FOUND",
             Self::EmbeddingFailed => "EMBEDDING_FAILED",
+            Self::EmbeddingsNotBuilt => "EMBEDDINGS_NOT_BUILT",
             Self::NotFound => "NOT_FOUND",
             Self::Ambiguous => "AMBIGUOUS",
+            Self::HealthCheckFailed => "HEALTH_CHECK_FAILED",
+            Self::UsageError => "USAGE_ERROR",
             Self::SurgicalPreflightFailed => "SURGICAL_PREFLIGHT_FAILED",
         };
         write!(f, "{code}")
@@ -79,8 +85,11 @@ impl ErrorCode {
             Self::OllamaUnavailable => 14,
             Self::OllamaModelNotFound => 15,
             Self::EmbeddingFailed => 16,
+            Self::EmbeddingsNotBuilt => 21,
             Self::NotFound => 17,
             Self::Ambiguous => 18,
+            Self::HealthCheckFailed => 19,
+            Self::UsageError => 2,
             // Shares exit code 6 with GitLabNotFound — same semantic category (resource not found).
             // Robot consumers distinguish via ErrorCode string, not exit code.
             Self::SurgicalPreflightFailed => 6,
@@ -201,7 +210,7 @@ impl LoreError {
             Self::OllamaUnavailable { .. } => ErrorCode::OllamaUnavailable,
             Self::OllamaModelNotFound { .. } => ErrorCode::OllamaModelNotFound,
             Self::EmbeddingFailed { .. } => ErrorCode::EmbeddingFailed,
-            Self::EmbeddingsNotBuilt => ErrorCode::EmbeddingFailed,
+            Self::EmbeddingsNotBuilt => ErrorCode::EmbeddingsNotBuilt,
             Self::SurgicalPreflightFailed { .. } => ErrorCode::SurgicalPreflightFailed,
         }
     }

src/embedding/chunk_ids.rs

@@ -1,70 +0,0 @@
-pub const CHUNK_ROWID_MULTIPLIER: i64 = 1000;
-
-pub fn encode_rowid(document_id: i64, chunk_index: i64) -> i64 {
-    assert!(
-        (0..CHUNK_ROWID_MULTIPLIER).contains(&chunk_index),
-        "chunk_index {chunk_index} out of range [0, {CHUNK_ROWID_MULTIPLIER})"
-    );
-    document_id
-        .checked_mul(CHUNK_ROWID_MULTIPLIER)
-        .and_then(|v| v.checked_add(chunk_index))
-        .unwrap_or_else(|| {
-            panic!("encode_rowid overflow: document_id={document_id}, chunk_index={chunk_index}")
-        })
-}
-
-pub fn decode_rowid(rowid: i64) -> (i64, i64) {
-    assert!(
-        rowid >= 0,
-        "decode_rowid called with negative rowid: {rowid}"
-    );
-    let document_id = rowid / CHUNK_ROWID_MULTIPLIER;
-    let chunk_index = rowid % CHUNK_ROWID_MULTIPLIER;
-    (document_id, chunk_index)
-}
-
-#[cfg(test)]
-mod tests {
-    use super::*;
-
-    #[test]
-    fn test_encode_single_chunk() {
-        assert_eq!(encode_rowid(1, 0), 1000);
-    }
-
-    #[test]
-    fn test_encode_multi_chunk() {
-        assert_eq!(encode_rowid(1, 5), 1005);
-    }
-
-    #[test]
-    fn test_encode_specific_values() {
-        assert_eq!(encode_rowid(42, 0), 42000);
-        assert_eq!(encode_rowid(42, 5), 42005);
-    }
-
-    #[test]
-    fn test_decode_zero_chunk() {
-        assert_eq!(decode_rowid(42000), (42, 0));
-    }
-
-    #[test]
-    fn test_decode_roundtrip() {
-        for doc_id in [0, 1, 42, 100, 999, 10000] {
-            for chunk_idx in [0, 1, 5, 99, 999] {
-                let rowid = encode_rowid(doc_id, chunk_idx);
-                let (decoded_doc, decoded_chunk) = decode_rowid(rowid);
-                assert_eq!(
-                    (decoded_doc, decoded_chunk),
-                    (doc_id, chunk_idx),
-                    "Roundtrip failed for doc_id={doc_id}, chunk_idx={chunk_idx}"
-                );
-            }
-        }
-    }
-
-    #[test]
-    fn test_multiplier_value() {
-        assert_eq!(CHUNK_ROWID_MULTIPLIER, 1000);
-    }
-}

src/embedding/chunking.rs

@@ -1,107 +0,0 @@
-pub const CHUNK_MAX_BYTES: usize = 1_500;
-
-pub const EXPECTED_DIMS: usize = 768;
-
-pub const CHUNK_OVERLAP_CHARS: usize = 200;
-
-pub fn split_into_chunks(content: &str) -> Vec<(usize, String)> {
-    if content.is_empty() {
-        return Vec::new();
-    }
-
-    if content.len() <= CHUNK_MAX_BYTES {
-        return vec![(0, content.to_string())];
-    }
-
-    let mut chunks: Vec<(usize, String)> = Vec::new();
-    let mut start = 0;
-    let mut chunk_index = 0;
-
-    while start < content.len() {
-        let remaining = &content[start..];
-        if remaining.len() <= CHUNK_MAX_BYTES {
-            chunks.push((chunk_index, remaining.to_string()));
-            break;
-        }
-
-        let end = floor_char_boundary(content, start + CHUNK_MAX_BYTES);
-        let window = &content[start..end];
-
-        let split_at = find_paragraph_break(window)
-            .or_else(|| find_sentence_break(window))
-            .or_else(|| find_word_break(window))
-            .unwrap_or(window.len());
-
-        let chunk_text = &content[start..start + split_at];
-        chunks.push((chunk_index, chunk_text.to_string()));
-
-        let advance = if split_at > CHUNK_OVERLAP_CHARS {
-            split_at - CHUNK_OVERLAP_CHARS
-        } else {
-            split_at
-        }
-        .max(1);
-        let old_start = start;
-        start += advance;
-        // Ensure start lands on a char boundary after overlap subtraction
-        start = floor_char_boundary(content, start);
-        // Guarantee forward progress: multi-byte chars can cause
-        // floor_char_boundary to round back to old_start
-        if start <= old_start {
-            start = old_start
-                + content[old_start..]
-                    .chars()
-                    .next()
-                    .map_or(1, |c| c.len_utf8());
-        }
-        chunk_index += 1;
-    }
-
-    chunks
-}
-
-fn find_paragraph_break(window: &str) -> Option<usize> {
-    let search_start = floor_char_boundary(window, window.len() * 2 / 3);
-    window[search_start..]
-        .rfind("\n\n")
-        .map(|pos| search_start + pos + 2)
-        .or_else(|| window[..search_start].rfind("\n\n").map(|pos| pos + 2))
-}
-
-fn find_sentence_break(window: &str) -> Option<usize> {
-    let search_start = floor_char_boundary(window, window.len() / 2);
-    for pat in &[". ", "? ", "! "] {
-        if let Some(pos) = window[search_start..].rfind(pat) {
-            return Some(search_start + pos + pat.len());
-        }
-    }
-    for pat in &[". ", "? ", "! "] {
-        if let Some(pos) = window[..search_start].rfind(pat) {
-            return Some(pos + pat.len());
-        }
-    }
-    None
-}
-
-fn find_word_break(window: &str) -> Option<usize> {
-    let search_start = floor_char_boundary(window, window.len() / 2);
-    window[search_start..]
-        .rfind(' ')
-        .map(|pos| search_start + pos + 1)
-        .or_else(|| window[..search_start].rfind(' ').map(|pos| pos + 1))
-}
-
-fn floor_char_boundary(s: &str, idx: usize) -> usize {
-    if idx >= s.len() {
-        return s.len();
-    }
-    let mut i = idx;
-    while i > 0 && !s.is_char_boundary(i) {
-        i -= 1;
-    }
-    i
-}
-
-#[cfg(test)]
-#[path = "chunking_tests.rs"]
-mod tests;

src/gitlab/transformers/discussion.rs

@@ -53,14 +53,8 @@ pub struct NormalizedNote {
     pub position_head_sha: Option<String>,
 }
 
-fn parse_timestamp(ts: &str) -> i64 {
-    match iso_to_ms(ts) {
-        Some(ms) => ms,
-        None => {
-            warn!(timestamp = ts, "Invalid timestamp, defaulting to epoch 0");
-            0
-        }
-    }
+fn parse_timestamp(ts: &str) -> Result<i64, String> {
+    iso_to_ms_strict(ts)
 }
 
 pub fn transform_discussion(
@@ -133,7 +127,15 @@ pub fn transform_notes(
         .notes
         .iter()
         .enumerate()
-        .map(|(idx, note)| transform_single_note(note, local_project_id, idx as i32, now))
+        .filter_map(|(idx, note)| {
+            match transform_single_note(note, local_project_id, idx as i32, now) {
+                Ok(n) => Some(n),
+                Err(e) => {
+                    warn!(note_id = note.id, error = %e, "Skipping note with invalid timestamp");
+                    None
+                }
+            }
+        })
         .collect()
 }
 
@@ -142,7 +144,10 @@ fn transform_single_note(
     local_project_id: i64,
     position: i32,
     now: i64,
-) -> NormalizedNote {
+) -> Result<NormalizedNote, String> {
+    let created_at = parse_timestamp(&note.created_at)?;
+    let updated_at = parse_timestamp(&note.updated_at)?;
+
     let (
         position_old_path,
         position_new_path,
@@ -156,7 +161,7 @@ fn transform_single_note(
         position_head_sha,
     ) = extract_position_fields(&note.position);
 
-    NormalizedNote {
+    Ok(NormalizedNote {
         gitlab_id: note.id,
         project_id: local_project_id,
         note_type: note.note_type.clone(),
@@ -164,8 +169,8 @@ fn transform_single_note(
         author_id: Some(note.author.id),
         author_username: note.author.username.clone(),
         body: note.body.clone(),
-        created_at: parse_timestamp(&note.created_at),
-        updated_at: parse_timestamp(&note.updated_at),
+        created_at,
+        updated_at,
         last_seen_at: now,
         position,
         resolvable: note.resolvable,
@@ -182,7 +187,7 @@ fn transform_single_note(
         position_base_sha,
         position_start_sha,
         position_head_sha,
-    }
+    })
 }
 
 #[allow(clippy::type_complexity)]

src/main.rs

@@ -13,23 +13,24 @@ use lore::cli::autocorrect::{self, CorrectionResult};
 use lore::cli::commands::{
     IngestDisplay, InitInputs, InitOptions, InitResult, ListFilters, MrListFilters,
     NoteListFilters, RefreshOptions, RefreshResult, SearchCliFilters, SyncOptions, TimelineParams,
-    delete_orphan_projects, open_issue_in_browser, open_mr_in_browser, parse_trace_path,
-    print_count, print_count_json, print_cron_install, print_cron_install_json, print_cron_status,
-    print_cron_status_json, print_cron_uninstall, print_cron_uninstall_json, print_doctor_results,
-    print_drift_human, print_drift_json, print_dry_run_preview, print_dry_run_preview_json,
-    print_embed, print_embed_json, print_event_count, print_event_count_json, print_file_history,
-    print_file_history_json, print_generate_docs, print_generate_docs_json, print_ingest_summary,
-    print_ingest_summary_json, print_list_issues, print_list_issues_json, print_list_mrs,
-    print_list_mrs_json, print_list_notes, print_list_notes_json, print_related_human,
-    print_related_json, print_search_results, print_search_results_json, print_show_issue,
-    print_show_issue_json, print_show_mr, print_show_mr_json, print_stats, print_stats_json,
-    print_sync, print_sync_json, print_sync_status, print_sync_status_json, print_timeline,
-    print_timeline_json_with_meta, print_trace, print_trace_json, print_who_human, print_who_json,
-    query_notes, run_auth_test, run_count, run_count_events, run_cron_install, run_cron_status,
-    run_cron_uninstall, run_doctor, run_drift, run_embed, run_file_history, run_generate_docs,
-    run_ingest, run_ingest_dry_run, run_init, run_init_refresh, run_list_issues, run_list_mrs,
-    run_me, run_related, run_search, run_show_issue, run_show_mr, run_stats, run_sync,
-    run_sync_status, run_timeline, run_token_set, run_token_show, run_who,
+    delete_orphan_projects, handle_explain, open_issue_in_browser, open_mr_in_browser,
+    parse_trace_path, print_count, print_count_json, print_cron_install, print_cron_install_json,
+    print_cron_status, print_cron_status_json, print_cron_uninstall, print_cron_uninstall_json,
+    print_doctor_results, print_drift_human, print_drift_json, print_dry_run_preview,
+    print_dry_run_preview_json, print_embed, print_embed_json, print_event_count,
+    print_event_count_json, print_file_history, print_file_history_json, print_generate_docs,
+    print_generate_docs_json, print_ingest_summary, print_ingest_summary_json, print_list_issues,
+    print_list_issues_json, print_list_mrs, print_list_mrs_json, print_list_notes,
+    print_list_notes_json, print_related_human, print_related_json, print_search_results,
+    print_search_results_json, print_show_issue, print_show_issue_json, print_show_mr,
+    print_show_mr_json, print_stats, print_stats_json, print_sync, print_sync_json,
+    print_sync_status, print_sync_status_json, print_timeline, print_timeline_json_with_meta,
+    print_trace, print_trace_json, print_who_human, print_who_json, query_notes, run_auth_test,
+    run_count, run_count_events, run_cron_install, run_cron_status, run_cron_uninstall, run_doctor,
+    run_drift, run_embed, run_file_history, run_generate_docs, run_ingest, run_ingest_dry_run,
+    run_init, run_init_refresh, run_list_issues, run_list_mrs, run_me, run_related, run_search,
+    run_show_issue, run_show_mr, run_stats, run_sync, run_sync_status, run_timeline, run_token_set,
+    run_token_show, run_who,
 };
 use lore::cli::render::{ColorMode, GlyphMode, Icons, LoreRenderer, Theme};
 use lore::cli::robot::{RobotMeta, strip_schemas};
@@ -222,6 +223,25 @@ fn main() {
         Some(Commands::Trace(args)) => handle_trace(cli.config.as_deref(), args, robot_mode),
         Some(Commands::Cron(args)) => handle_cron(cli.config.as_deref(), args, robot_mode),
         Some(Commands::Token(args)) => handle_token(cli.config.as_deref(), args, robot_mode).await,
+        Some(Commands::Explain {
+            entity_type,
+            iid,
+            project,
+            sections,
+            no_timeline,
+            max_decisions,
+            since,
+        }) => handle_explain(
+            cli.config.as_deref(),
+            &entity_type,
+            iid,
+            project.as_deref(),
+            sections,
+            no_timeline,
+            max_decisions,
+            since.as_deref(),
+            robot_mode,
+        ),
         Some(Commands::Drift {
             entity_type,
             iid,

src/search/fts.rs

@@ -119,15 +119,12 @@ pub fn search_fts(
 }
 
 pub fn generate_fallback_snippet(content_text: &str, max_chars: usize) -> String {
-    if content_text.chars().count() <= max_chars {
-        return content_text.to_string();
-    }
-
-    let byte_end = content_text
-        .char_indices()
-        .nth(max_chars)
-        .map(|(i, _)| i)
-        .unwrap_or(content_text.len());
+    // Use char_indices to find the boundary at max_chars in a single pass,
+    // short-circuiting early for large strings instead of counting all chars.
+    let byte_end = match content_text.char_indices().nth(max_chars) {
+        Some((i, _)) => i,
+        None => return content_text.to_string(), // content fits within max_chars
+    };
     let truncated = &content_text[..byte_end];
 
     if let Some(last_space) = truncated.rfind(' ') {

src/timeline/seed.rs

@@ -411,7 +411,9 @@ fn round_robin_select_by_discussion(
         let mut made_progress = false;
 
         for (disc_idx, &discussion_id) in discussion_order.iter().enumerate() {
-            let notes = by_discussion.get(&discussion_id).unwrap();
+            let notes = by_discussion
+                .get(&discussion_id)
+                .expect("key present: inserted into by_discussion via discussion_order");
             let note_idx = indices[disc_idx];
 
             if note_idx < notes.len() {