refactor: rename Mode variants C/A to Lexical/Hybrid (closes #2)

The retrieval-mode enum used opaque single letters `Mode { C, A }`;
neither the identifier nor the operator-facing `--mode a` token
conveyed what the mode does. Rename to self-describing names that map
directly onto the glossary definitions:

  Mode::C -> Mode::Lexical  (BM25 + tag filter, offline, no IONOS)
  Mode::A -> Mode::Hybrid   (lexical u semantic -> RRF -> rerank)

Decisions taken (the issue's open questions, resolved):
- CLI canonical tokens are now `lexical` / `hybrid`; the default is
  `lexical`. The legacy `c` / `a` tokens stay accepted as
  case-insensitive input aliases (zero cost; protects hand-typed
  invocations). A unit test pins the alias contract.
- The diagnostics `mode` string (Debug-derived) now emits
  "Lexical"/"Hybrid". Verified safe: no downstream consumer parses it.
  doctate is the future integrator and embeds the library (the `Mode`
  enum), not the JSON string (design spec §103).
- The reserved, out-of-scope generative tier (spec's "Mode B") keeps
  conceptual room: a future `Mode::Generative` does not collide with
  the retrieval-strategy names Lexical/Hybrid.

Surface: enum + FromStr, CLI defaults and `eval --mode both`
expansion, the private `collect_mode_c`/`collect_mode_a` methods (now
`collect_lexical`/`collect_hybrid`) and their comments, the two
pipeline mode test files (renamed), the eval CLI test, the glossary
(old letter forms demoted to Avoid lists), and the spec CLI synopsis.

closes #2

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

docs/glossary.md

@@ -20,13 +20,13 @@ The BfArM Alpha-ID dataset mapping free-text diagnosis phrases to ICD-10-GM code
 **Avoid:** segment, unit, Einheit, Formulierung
 One caller-extracted diagnostic phrase (one input line) — the unit that is matched and ranked. In source code this concept is carried by the identifier `segment` (e.g. `split_segments`, `source_segments`), which is retained as a code term only.
 
-### Mode C
-**Avoid:** Modus C
-The lexical-baseline retrieval mode: BM25 over the corpus plus tag filtering, with no IONOS calls. Also the degrade target for Mode A.
+### Mode Lexical
+**Avoid:** Mode C, Modus C, mode c
+The lexical-baseline retrieval mode: BM25 over the corpus plus tag filtering, with no IONOS calls. Also the degrade target for Mode Hybrid.
 
-### Mode A
-**Avoid:** Modus A, semantic mode
-The hybrid retrieval mode: lexical and semantic (IONOS embedding) pools fused via RRF, then cross-encoder reranked. Degrades to Mode C on any IONOS failure.
+### Mode Hybrid
+**Avoid:** Mode A, Modus A, mode a, semantic mode
+The hybrid retrieval mode: lexical and semantic (IONOS embedding) pools fused via RRF, then cross-encoder reranked. Degrades to Mode Lexical on any IONOS failure.
 
 ### billable
 **Avoid:** abrechenbar, Abrechenbarkeit
@@ -42,11 +42,11 @@ The ClaML process of generating terminal sub-digit codes (e.g. `E11.90`) by appl
 
 ### RRF
 **Avoid:** —
-Reciprocal Rank Fusion: the rank-based method that merges the lexical and semantic candidate lists into one fused pool in Mode A.
+Reciprocal Rank Fusion: the rank-based method that merges the lexical and semantic candidate lists into one fused pool in Mode Hybrid.
 
 ### rerank
 **Avoid:** —
-The Mode A cross-encoder step that rescores the fused candidate pool against the query phrase, using the IONOS reranker model.
+The Mode Hybrid cross-encoder step that rescores the fused candidate pool against the query phrase, using the IONOS reranker model.
 
 ### corpus
 **Avoid:** Korpus, match corpus
@@ -58,11 +58,11 @@ The per-phrase, content-hash-keyed persistent store of corpus embeddings under `
 
 ### vector index
 **Avoid:** ANN index
-The in-RAM matrix of corpus embeddings searched by exact cosine similarity for the semantic pool. Built only when every corpus entry has a cached embedding; otherwise Mode A degrades.
+The in-RAM matrix of corpus embeddings searched by exact cosine similarity for the semantic pool. Built only when every corpus entry has a cached embedding; otherwise Mode Hybrid degrades.
 
 ### degrade
 **Avoid:** —
-Mode A falling back to Mode C when any IONOS step fails (embed, rerank, or a missing vector index); the request is still answered and `degraded` is set in diagnostics. Distinct from the 5-char-parent lookup fallback in `meta_lookup`.
+Mode Hybrid falling back to Mode Lexical when any IONOS step fails (embed, rerank, or a missing vector index); the request is still answered and `degraded` is set in diagnostics. Distinct from the 5-char-parent lookup fallback in `meta_lookup`.
 
 ### tag filter
 **Avoid:** —

docs/specs/2026-05-18-alpha-id-icd-suggestion-design.md

@@ -197,9 +197,9 @@ alpha-id index build [--sample N | --full] [--confirm]
                                   #   Korpus+ClaML parsen, bge-m3-Embeddings,
                                   #   Lexik-+Vektorindex persistieren (resumierbar)
 alpha-id suggest [FILE|-]         # Formulierungs-Liste (eine pro Zeile) → Top-10
-   --mode c|a  --top 10  --billable-only  --valid-only
+   --mode lexical|hybrid  --top 10  --billable-only  --valid-only
    --chapters I,J  --exclude-exotic  --json|--table
-alpha-id eval --mode c|a --cases N --seed S [--gold PATH]
+alpha-id eval --mode lexical|hybrid --cases N --seed S [--gold PATH]
 ```
 
 - Config-TOML: IONOS-Endpoint/Modellnamen/Pool-Größen/Pfad-Defaults, per Flags überschreibbar.

src/bin/alpha_id.rs

@@ -19,7 +19,7 @@ enum Cmd {
     /// Suggest ICD codes for a dictation (FILE or - for stdin)
     Suggest {
         input: String,
-        #[arg(long, default_value = "c")] mode: String,
+        #[arg(long, default_value = "lexical")] mode: String,
         #[arg(long, default_value_t = 10)] top: usize,
         #[arg(long)] billable_only: bool,
         #[arg(long)] valid_only: bool,
@@ -29,7 +29,7 @@ enum Cmd {
     },
     /// Run the eval harness
     Eval {
-        #[arg(long, default_value = "c")] mode: String,
+        #[arg(long, default_value = "lexical")] mode: String,
         #[arg(long, default_value_t = 200)] cases: usize,
         #[arg(long, default_value_t = 42)] seed: u64,
     },
@@ -152,7 +152,7 @@ fn main() {
         }
         Cmd::Eval { mode, cases, seed } => {
             let modes: Vec<Mode> = if mode == "both" {
-                vec![Mode::C, Mode::A]
+                vec![Mode::Lexical, Mode::Hybrid]
             } else {
                 vec![mode.parse().expect("mode")]
             };

src/model.rs

@@ -78,14 +78,14 @@ impl Filter {
 }
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
-pub enum Mode { C, A }
+pub enum Mode { Lexical, Hybrid }
 
 impl FromStr for Mode {
     type Err = String;
     fn from_str(s: &str) -> Result<Self, String> {
         match s.to_ascii_lowercase().as_str() {
-            "c" => Ok(Mode::C),
-            "a" => Ok(Mode::A),
+            "lexical" | "c" => Ok(Mode::Lexical),
+            "hybrid" | "a" => Ok(Mode::Hybrid),
             other => Err(format!("unknown mode: {other}")),
         }
     }

src/pipeline.rs

@@ -38,8 +38,8 @@ impl Pipeline {
             m
         };
         // Build the semantic index only if EVERY corpus entry already has a
-        // cached embedding; otherwise leave it `None` so Mode A degrades to C
-        // rather than mispairing partial vectors.
+        // cached embedding; otherwise leave it `None` so Mode Hybrid degrades to
+        // Lexical rather than mispairing partial vectors.
         let vector = match EmbeddingStore::open(&cfg.index_dir, &cfg.embed_model) {
             Ok(store) if entries.iter().all(|e| store.has(&e.text)) => {
                 let vecs: Option<Vec<Vec<f32>>> =
@@ -108,9 +108,9 @@ impl Pipeline {
         })
     }
 
-    /// Mode C candidate collection: lexical pool per segment. This is the
-    /// exact original behavior; it is also the degrade fallback for Mode A.
-    fn collect_mode_c(&self, segments: &[String]) -> Vec<Candidate> {
+    /// Mode Lexical candidate collection: lexical pool per segment. This is the
+    /// exact original behavior; it is also the degrade fallback for Mode Hybrid.
+    fn collect_lexical(&self, segments: &[String]) -> Vec<Candidate> {
         let mut candidates: Vec<Candidate> = Vec::new();
         for (si, seg) in segments.iter().enumerate() {
             let lex = self.lexical.search(seg, self.pool_size).unwrap_or_default();
@@ -131,11 +131,11 @@ impl Pipeline {
         candidates
     }
 
-    /// Mode A candidate collection: per segment, fuse a lexical pool with a
+    /// Mode Hybrid candidate collection: per segment, fuse a lexical pool with a
     /// semantic pool (IONOS embedding + in-RAM vector search) via RRF, then
     /// cross-encoder rerank the fused pool. ANY error (IONOS unreachable, no
     /// vector index, embed/rerank failure) propagates so `suggest` degrades.
-    fn collect_mode_a(&self, segments: &[String], calls: &mut usize)
+    fn collect_hybrid(&self, segments: &[String], calls: &mut usize)
         -> Result<Vec<Candidate>, AppError> {
         let client = IonosClient::new(&self.cfg.ionos_base_url, &self.cfg.token_path)?;
         let vector = self.vector.as_ref()
@@ -199,14 +199,14 @@ impl Pipeline {
         let mut degraded = false;
 
         let candidates: Vec<Candidate> = match mode {
-            Mode::C => self.collect_mode_c(&segments),
-            Mode::A => match self.collect_mode_a(&segments, &mut ionos_calls) {
+            Mode::Lexical => self.collect_lexical(&segments),
+            Mode::Hybrid => match self.collect_hybrid(&segments, &mut ionos_calls) {
                 Ok(c) => c,
                 Err(_) => {
-                    // Total degradation: any failure → Mode C fallback,
+                    // Total degradation: any failure → Mode Lexical fallback,
                     // request still answered, never panics.
                     degraded = true;
-                    self.collect_mode_c(&segments)
+                    self.collect_lexical(&segments)
                 }
             },
         };

tests/cli_tests.rs

@@ -12,3 +12,21 @@ fn cli_suggest_outputs_json_with_codes() {
     assert!(s.contains("\"icd_code\""));
     assert!(s.contains("E11"));
 }
+
+/// The renamed canonical CLI token `--mode lexical` is accepted and the
+/// diagnostics line reports the new variant name `Lexical` (not the legacy `C`),
+/// confirming the enum rename reaches observable CLI output.
+#[test]
+fn cli_suggest_accepts_canonical_lexical_token() {
+    let out = Command::new(env!("CARGO_BIN_EXE_alpha-id"))
+        .args(["suggest", "--mode", "lexical", "-"])
+        .arg("--config").arg("config/default.toml")
+        .env("ALPHA_ID_STDIN", "Diabetes mellitus Typ 2")
+        .output().unwrap();
+    assert!(out.status.success(), "stderr: {}", String::from_utf8_lossy(&out.stderr));
+    let stdout = String::from_utf8_lossy(&out.stdout);
+    assert!(stdout.contains("E11"));
+    let stderr = String::from_utf8_lossy(&out.stderr);
+    assert!(stderr.contains("mode Lexical"),
+        "diagnostics should report canonical mode name; stderr: {stderr}");
+}

tests/eval_compare_tests.rs

@@ -1,9 +1,9 @@
 use std::process::Command;
 
 #[test]
-fn eval_mode_c_runs_and_reports_billable_recall() {
+fn eval_lexical_runs_and_reports_billable_recall() {
     let out = Command::new(env!("CARGO_BIN_EXE_alpha-id"))
-        .args(["eval", "--mode", "c", "--cases", "30"])
+        .args(["eval", "--mode", "lexical", "--cases", "30"])
         .arg("--config").arg("config/default.toml")
         .output().unwrap();
     assert!(out.status.success(), "stderr: {}", String::from_utf8_lossy(&out.stderr));
@@ -15,7 +15,7 @@ fn eval_mode_c_runs_and_reports_billable_recall() {
 fn eval_is_deterministic_same_seed() {
     let run = || {
         let out = Command::new(env!("CARGO_BIN_EXE_alpha-id"))
-            .args(["eval", "--mode", "c", "--cases", "40", "--seed", "42"])
+            .args(["eval", "--mode", "lexical", "--cases", "40", "--seed", "42"])
             .arg("--config").arg("config/default.toml")
             .output().unwrap();
         assert!(out.status.success(), "stderr: {}", String::from_utf8_lossy(&out.stderr));

tests/model_tests.rs

@@ -15,6 +15,15 @@ fn filter_default_accepts_everything() {
 
 #[test]
 fn mode_parses_from_str() {
-    assert_eq!("a".parse::<Mode>().unwrap(), Mode::A);
-    assert_eq!("c".parse::<Mode>().unwrap(), Mode::C);
+    assert_eq!("lexical".parse::<Mode>().unwrap(), Mode::Lexical);
+    assert_eq!("hybrid".parse::<Mode>().unwrap(), Mode::Hybrid);
+}
+
+#[test]
+fn mode_letter_aliases_still_parse_to_new_variants() {
+    // The legacy `c`/`a` CLI tokens remain accepted aliases (case-insensitive)
+    // for the renamed canonical `lexical`/`hybrid` modes.
+    assert_eq!("c".parse::<Mode>().unwrap(), Mode::Lexical);
+    assert_eq!("a".parse::<Mode>().unwrap(), Mode::Hybrid);
+    assert_eq!("A".parse::<Mode>().unwrap(), Mode::Hybrid);
 }

tests/pipeline_hybrid_tests.rs

@@ -2,11 +2,11 @@ use alpha_id::pipeline::Pipeline;
 use alpha_id::model::{Config, Filter, Mode};
 
 #[test]
-fn mode_a_degrades_to_c_when_ionos_unreachable() {
+fn hybrid_degrades_to_lexical_when_ionos_unreachable() {
     let mut cfg = Config::load("config/default.toml").unwrap();
     cfg.ionos_base_url = "http://127.0.0.1:1".into(); // refused
     let p = Pipeline::load(&cfg).unwrap();
-    let res = p.suggest("Diabetes mellitus Typ 2", Mode::A, &Filter::default(), 10);
+    let res = p.suggest("Diabetes mellitus Typ 2", Mode::Hybrid, &Filter::default(), 10);
     assert!(res.diagnostics.degraded);                 // fell back
     assert!(!res.suggestions.is_empty());              // still answered
     assert!(res.suggestions.iter().any(|s| s.icd_code.starts_with("E11")));

tests/pipeline_lexical_tests.rs

@@ -6,23 +6,23 @@ fn cfg() -> Config {
 }
 
 #[test]
-fn mode_c_end_to_end_real_data() {
+fn lexical_end_to_end_real_data() {
     let p = Pipeline::load(&cfg()).unwrap();
     let dictation = "Patient mit Diabetes mellitus Typ 2\n\nArterielle Hypertonie";
-    let res = p.suggest(dictation, Mode::C, &Filter::default(), 10);
+    let res = p.suggest(dictation, Mode::Lexical, &Filter::default(), 10);
     assert!(!res.suggestions.is_empty());
     assert!(res.suggestions.len() <= 10);
     assert!(res.suggestions.iter().any(|s| s.icd_code.starts_with("E11")));
     assert!(res.suggestions.iter().any(|s| s.icd_code.starts_with("I10")));
     assert_eq!(res.diagnostics.segment_count, 2);
-    assert_eq!(res.diagnostics.mode, "C");
+    assert_eq!(res.diagnostics.mode, "Lexical");
 }
 
 #[test]
 fn billable_only_filter_excludes_three_digit_v_codes() {
     let p = Pipeline::load(&cfg()).unwrap();
     let f = Filter { billable_only: true, valid_only: true, chapters: None, exclude_exotic: false };
-    let res = p.suggest("Cholera", Mode::C, &f, 10);
+    let res = p.suggest("Cholera", Mode::Lexical, &f, 10);
     assert!(res.suggestions.iter().all(|s| s.tags.billable && s.tags.valid));
 }
 
@@ -30,7 +30,7 @@ fn billable_only_filter_excludes_three_digit_v_codes() {
 fn billable_only_keeps_diabetes_5th_digit_codes() {
     let p = Pipeline::load(&cfg()).unwrap();
     let f = Filter { billable_only: true, valid_only: true, chapters: None, exclude_exotic: false };
-    let res = p.suggest("Diabetes mellitus Typ 2", Mode::C, &f, 10);
+    let res = p.suggest("Diabetes mellitus Typ 2", Mode::Lexical, &f, 10);
     assert!(res.suggestions.iter().any(|s| s.icd_code.starts_with("E11") && s.tags.billable),
         "billable E11.x must survive --billable-only; got {:?}",
         res.suggestions.iter().map(|s| (&s.icd_code, s.tags.billable)).collect::<Vec<_>>());