docs: clarify query pipeline, Findere trick, and input formats

Fix a stray prefix in the README heading and update documentation to reflect the query pipeline's operation on `s-mers` (`s = k - z + 1`) with post-partition z-window filtering. Clarify the Findere trick, including k-mer size reduction, consecutive match requirements, and false positive rate calculations. Additionally, expand input format documentation to cover supported file extensions, gzip compression, recursive directory handling, and `query` command specifications.

README.md

@@ -1 +1,107 @@
-toto
+# obikmer
+
+`obikmer` is a Rust toolkit for indexing, querying, and comparing DNA sequences
+represented as sets of k-mers. It targets individual genome datasets (tens of
+Gbases) with maximum efficiency in computation, memory, and disk usage.
+
+## Key principles
+
+**Compact k-mer encoding.** Each k-mer is stored in a `u64` at 2 bits/base.
+k is odd, k ∈ [11, 31], fixed at runtime. The canonical form `min(kmer, revcomp(kmer))`
+halves the effective space by collapsing both strands.
+
+**Superkmer-based partitioning.** Sequences are decomposed into superkmers —
+maximal runs of k-mers sharing the same minimizer. Superkmers route naturally to
+partitions via the minimizer hash, enabling partition-parallel indexing and querying
+with no cross-partition communication.
+
+**Layered MPHF index.** Each partition holds a stack of layers. Each layer is a
+minimal perfect hash function (MPHF) over the k-mers of one input genome, paired
+with a per-genome presence/count matrix. Queries scatter k-mers to their partition,
+probe each layer in order, and aggregate results.
+
+**Approximate indexing (Findere).** With `-z Z`, the index stores k-mers of size
+`s = k − z + 1` instead of k. At query time, results are produced at size s, then
+a per-genome sliding window of size z aggregates z consecutive s-mer hits into one
+confirmed k-mer answer. This reduces the false-positive rate from `1/2^b` per s-mer
+to `1/2^(b·z)` per k-mer, at the cost of z−1 unconfirmed positions at each sequence
+break. The aggregation window spans the full query sequence, not individual superkmers,
+to avoid false negatives at superkmer boundaries.
+
+**Multi-genome.** A single index can hold any number of genomes. Each k-mer slot
+carries a per-genome count or presence vector. Distance matrices, NJ/UPGMA trees,
+and classification are derived from these vectors without rebuilding the index.
+
+## Input formats
+
+    Command              Formats accepted
+    ───────────────────  ──────────────────────────────────────────────────────────────
+    index, superkmer     FASTA (.fa .fasta), FASTQ (.fq .fastq), GenBank flat file
+                         (.gb .gbk .gbff), all optionally gzip-compressed.
+                         Directories expanded recursively. Streaming stdin via -.
+    query                FASTA, FASTQ, optionally gzip-compressed. Stdin via -.
+
+Non-ACGT characters act as hard breaks between k-mer segments in all formats.
+
+## Commands
+
+    Command    Role
+    ─────────  ────────────────────────────────────────────────────────────────────
+    index      Build a genome index from sequence files.
+               Runs scatter → dereplicate → count → layered MPHF.
+               Resumes automatically if interrupted.
+    merge      Merge multiple independently built indexes into one.
+    rebuild    Filter and compact an existing index: apply count thresholds,
+               drop layers, rewrite as a single-layer index.
+    reindex    Convert evidence in-place across all layers:
+               exact (evidence.bin) ↔ approximate (fingerprint.bin).
+               Does not touch the MPHF or unitigs.
+    query      Query an index with FASTA/FASTQ sequences.
+               Annotates each sequence with per-genome k-mer match counts
+               and optional per-position coverage vectors (--detail).
+               Parallel over sequence chunks.
+    distance   Compute a pairwise Bray-Curtis or Jaccard distance matrix
+               between all indexed genomes.
+               Optionally outputs a Newick NJ or UPGMA tree.
+    annotate   Add or update genome metadata (taxonomy, etc.) from a CSV
+               file; or dump the current metadata as CSV.
+    estimate   Dry-run: resolve and print approximate-index parameters
+               (z, evidence bits b, FP rates) given any two of (b, z, fp).
+               Does not touch any index.
+    dump       Dump all indexed k-mers as CSV with per-genome counts or
+               presence flags.
+    superkmer  Extract superkmers from a sequence file and write to stdout.
+               Diagnostic / pipeline use.
+    unitig     Dump the unitig sequences stored in a built index. Debug use.
+    utils      Miscellaneous utilities.
+               --new-label NEW=OLD  renames a genome label in-place.
+
+## Quick start
+
+```sh
+# Build an exact index for two genomes
+obikmer index --kmer-size 31 --label genome_a genome_a.fa --output index/
+obikmer index --kmer-size 31 --label genome_b genome_b.fa --output index/
+
+# Convert to approximate index (z=5, 8-bit fingerprints)
+obikmer reindex --approx -z 5 --evidence-bits 8 index/
+
+# Query reads
+obikmer query index/ reads.fq.gz > annotated.fa
+
+# Pairwise distances
+obikmer distance index/ > distances.tsv
+```
+
+## Parameter constraints
+
+    Parameter              Constraint
+    ─────────────────────  ──────────────
+    k  (--kmer-size)       odd, 11 ≤ k ≤ 31
+    m  (--minimizer-size)  odd, 3 ≤ m ≤ k−1
+    z  (-z, --approx only) 1 ≤ z ≤ k−1
+
+## Documentation
+
+Extended architecture and implementation notes are in `docmd/`. Build with
+`make doc` (requires Python + MkDocs Material).

docmd/architecture/query.md

@@ -8,7 +8,7 @@ Given a set of query sequences, determine for each sequence how many of its k-me
 
 ## Input
 
-- Query sequences in FASTA or FASTQ format (gzip supported, streaming stdin supported).
+- Query sequences in FASTA or FASTQ format (gzip supported, streaming stdin supported). GenBank flat files are not supported at query time (only at index time).
 - Sequences shorter than k bases are silently skipped.
 - Non-ACGT characters are handled by the superkmer decomposition layer: they act as hard breaks, producing shorter superkmers (identical to the behaviour at indexing time).
 
@@ -19,45 +19,50 @@ Given a set of query sequences, determine for each sequence how many of its k-me
 The query follows the same superkmer-based partitioning strategy used at indexing time.
 
 ```
-for each batch of sequences:
+for each chunk of sequences (parallel workers via obipipeline):
-    build QueryBatch: decompose all sequences into superkmers, deduplicate
+    build QueryBatch: decompose all sequences into s-mers via superkmers, deduplicate
+    allocate seq_results[seq_idx][smer_pos] = None  ← per-sequence s-mer result vectors
     split superkmers by partition via minimiser hash
     for each partition p:
         query_partition(p, superkmers_routed_to_p)
             → load QueryLayer(s) for p
-            → for each kmer in each superkmer: MphfLayer::find(kmer)
+            → for each s-mer in each superkmer: MphfLayer::find(smer)
-        apply_findere(sk_kmer_results, effective_z)   ← per superkmer
+        fill seq_results[seq_idx][kmer_offset + j] from partition results
-        broadcast confirmed results back to each (seq_idx, kmer_offset)
+    for each sequence:
+        apply_findere(seq_results[seq_idx], effective_z)  ← per full sequence
+        accumulate confirmed k-mer results into acc and cov
     emit annotated sequences
 ```
 
 Superkmers that appear more than once in the batch (same sequence or across sequences) are deduplicated: each unique `RoutableSuperKmer` is queried once per partition, and the result is broadcast to every `SKDesc` entry that references it.
 
-Parallelism is **not yet active** in the current implementation: batches are processed sequentially on a single thread despite the `--threads` flag being parsed. The `QueryBatch` / `split_by_partition` design is structured to support per-partition parallelism in a future iteration.
+**Findere requires full-sequence aggregation.** `apply_findere` is applied once per sequence on the complete s-mer result vector, after all partitions have contributed. Applying it per superkmer would produce false negatives at superkmer boundaries, where the z-window spans two superkmers.
+
+Batches are processed in parallel via `obipipeline` workers; the `--threads` flag controls the number of worker threads.
 
 ---
 
 ## Findere z-window filter
 
-For approximate and hybrid index modes, a raw k-mer hit is a positive from the fingerprint test with false-positive rate 1/2^b. The Findere scheme reduces the effective FP rate to 1/2^(b·z) by requiring **z consecutive k-mers** to all test positive before any of them is counted as a confirmed match.
+For approximate index modes, the index physically stores s-mers of size `s = k_user − z + 1`. At query time, `set_k(s)` is in effect, so queries naturally produce s-mer results. `apply_findere` then aggregates z consecutive s-mer results into one k_user-mer answer:
-
-`apply_findere` implements this as a sliding-window confirmation, independently for each genome:
 
 ```rust
 fn apply_findere(
-    results: &[Option<Box<[u32]>>],
+    results: &[Option<Box<[u32]>>],  // N s-mer results
     z: usize,
     n_genomes: usize,
-) -> Vec<Option<Box<[u32]>>>
+) -> Vec<Option<Box<[u32]>>>         // N − z + 1 k_user-mer results
 ```
 
-For each genome g, a position i is confirmed if there exists at least one window of z consecutive positions `[j, j+z)` that contains i and where all z positions are present for g (i.e. `results[pos]` is `Some(row)` and `row[g] > 0`). The implementation uses a single O(n) sliding-window scan per genome.
+Input length N (s-mers), output length N − z + 1 (k_user-mers).
 
-Unconfirmed positions are zeroed in the returned row. If all genomes are zeroed for a position, it is returned as `None`.
+For each genome g independently, a sliding window of size z scans the input. Output position i is confirmed for genome g iff all z values `results[i..i+z][g]` are nonzero (`None` counts as zero for all genomes). The scan is O(n) per genome.
 
-**Short superkmers**: when a superkmer contains fewer than z k-mers, no complete z-window can be formed. Rather than discarding all results, `apply_findere` returns them unchanged (no filter applied). This avoids penalising legitimate short sequences near read ends.
+Output values come from `results[i]` (leftmost s-mer of each window); genomes not confirmed are zeroed. If all genomes are zero, the position is returned as `None`.
 
-**Exact indexes**: `z` is effectively 1 (every k-mer is its own window). `apply_findere` is a no-op.
+**Short sequences**: when the s-mer count is less than z, no complete window can form — `apply_findere` returns an empty vector. K-mers from sequences shorter than k_user are not emitted.
+
+**Exact indexes**: `z = 1`, `apply_findere` is a passthrough (output length = input length).
 
 ### Effective z at query time
 
@@ -105,20 +110,20 @@ genome_totals[g] += if presence { u32::from(v >= threshold) } else { v }
 
 ## Coverage vectors (`--detail`)
 
-When `--detail` is requested, a 3-D accumulator `cov[seq_idx][genome][kmer_pos]` is allocated before the partition loop, with dimensions derived from `batch.n_kmers`:
+When `--detail` is requested, a 3-D accumulator `cov[seq_idx][genome][kmer_pos]` is allocated after all partitions are queried, with dimensions derived from `n_kmers_out = n_smers − z + 1` (k_user-mer positions, not s-mer positions):
 
 ```
-cov[seq_idx][g][abs_pos] += contribution
+cov[seq_idx][g][pos] += contribution
-where abs_pos = desc.kmer_offset + local_pos  (absolute kmer position in the sequence)
+where pos is the k_user-mer index in the filtered (post-Findere) vector
 ```
 
-Coverage reflects confirmed k-mers only (post-Findere). The vectors are emitted in the JSON annotation under the key `"coverage"`.
+Coverage reflects confirmed k_user-mers only. The vectors are emitted in the JSON annotation under the key `"coverage"`.
 
 ---
 
 ## `kmer_missing` semantics
 
-`kmer_missing` counts k-mers that returned `None` from the index before Findere filtering — i.e. k-mers truly absent from every layer. K-mers that were found in the index but rejected by the z-window filter are not counted as missing.
+`kmer_missing` counts k_user-mer positions where the first s-mer (`seq_results[seq_idx][pos]`) is `None` — i.e. absent from the index entirely. K-mers where the z-window fails because a later s-mer is absent or zero are not counted as missing (the first s-mer being present is used as proxy for index membership).
 
 ---
 
@@ -151,7 +156,7 @@ Genome keys follow the iteration order of `meta.genomes`.
 | `kmer_strict_matches` | object | always | per-genome accumulated value (label → count or 0/1) |
 | `coverage` | object | `--detail` | per-genome array of per-position contributions (label → [u32]) |
 
-`kmer_count + kmer_missing` ≤ total k-mers in the sequence. The gap (if any) corresponds to k-mers found in the index but rejected by the Findere z-window filter.
+`kmer_count + kmer_missing` ≤ total k_user-mers in the sequence. The gap corresponds to k_user-mers whose z-window was not fully confirmed (at least one s-mer absent or zero for all genomes) but whose first s-mer was present in the index.
 
 ---
 
@@ -171,7 +176,7 @@ obikmer query <index> [--detail] [--mismatch] [--count-missing]
 | `--count-missing` | off | Add `kmer_missing` field to JSON |
 | `--force-presence` | off | Report 0/1 per genome regardless of index counts |
 | `--presence-threshold` | 1 | Minimum count to declare genome present |
-| `-T` / `--threads` | all CPUs | Worker threads (parallelism not yet active) |
+| `-T` / `--threads` | all CPUs | Worker threads |
 
 `--mismatch` is accepted but currently ignored with a warning on stderr.
 
@@ -181,5 +186,4 @@ obikmer query <index> [--detail] [--mismatch] [--count-missing]
 
 - **`--mismatch`**: 1-mismatch approximate matching — generate `3·k` single-substitution variants per k-mer, look each up independently.
 - **Read classification** (`--classify`): assign each read to the genome with the highest match score.
-- **Parallelism**: activate per-partition or per-sequence worker threads using the already-parsed `--threads` value.
 - **Whitelist / blacklist filtering**: threshold-based accept/reject on per-genome match scores.

docmd/implementation/evidence_elimination.md

@@ -35,15 +35,18 @@ stored at `s` belongs to the legitimate k-mer at that slot. The FP event is:
 P(FP per k-mer) = 1 / 2^b
 ```
 
-The Findere trick raises the effective window to z consecutive k-mers. A query
+The Findere trick reduces the indexed k-mer size. When the user specifies k_user
-succeeds only when all z fingerprint checks pass, reducing the per-window FP rate:
+and z, the index physically stores k-mers of size `s = k_user − z + 1`. At query
+time, the same s-mer size is used. After collecting per-position s-mer results
+over the full query sequence, a sliding window of size z aggregates z consecutive
+s-mer hits into one confirmed k_user-mer hit, reducing the per-window FP rate:
 
 ```
-P(FP per z-window) = 1 / 2^(b·z)
+P(FP per k_user-mer) = 1 / 2^(b·z)
 ```
 
-The effective indexed k-mer length is `k − z + 1`: a query for a (k+z−1)-mer
+`IndexConfig::kmer_size` stores `s = k_user − z + 1`, not k_user. Both indexing
-decomposes into z overlapping k-mers, all of which must match.
+and querying use this stored size via `set_k(idx.kmer_size())`.
 
 Parameters b and z are stored in `layer_meta.json` (`EvidenceKind::Approx { b, z }`).
 
@@ -167,12 +170,12 @@ any index. It accepts the same `--evidence-bits`, `-z`, and `--fp` flags and
 additionally accepts `-k` to display the effective indexed k-mer length:
 
 ```
-k (query):             31
+k (user):              31
-k (indexed):           31
+k (indexed, s=k-z+1):  27
-z:                     1
+z:                     5
 evidence bits (b):     8
-FP per k-mer:          3.906e-3  (1/2^8)
+FP per s-mer:          3.906e-3  (1/2^8)
-FP per z-window:       3.906e-3  (1/2^8)
+FP per k-mer window:   9.537e-7  (1/2^(8·5))
 ```
 
 Useful for choosing parameters before committing to an index build.

docmd/index.md

@@ -25,7 +25,8 @@
 - Maximum efficiency in computation, memory, and disk usage
 - k odd, k ∈ [11, 31], fixed at runtime; kmer fits in a u64 (2 bits/base)
 - Canonical form: `min(kmer, revcomp(kmer))` reduces strand-symmetric space by half
-- Input formats: FASTA, FASTQ, gzip, streaming stdin; `index` reads from stdin automatically when no input files are provided (`-` can also be passed explicitly among other paths)
+- Input formats for `index`/`superkmer`: FASTA (`.fa`, `.fasta`), FASTQ (`.fq`, `.fastq`), GenBank flat file (`.gb`, `.gbk`, `.gbff`), all optionally gzip-compressed; directories expanded recursively; streaming stdin via `-`
+- Input formats for `query`: FASTA, FASTQ, optionally gzip-compressed; streaming stdin via `-`
 
 ## Parameter constraints (enforced at CLI)