⬆️ version bump to v4.5

- Update obioptions.Version from "Release 4.4.29" to "/v/ Release v5"
- Update version.txt from 4.29 → .30
(automated by Makefile)

autodoc/docmd/pkg/obialign/backtracking.md

@@ -0,0 +1,30 @@
+# Semantic Description of `obialign` Backtracking Module
+
+The `_Backtracking` function implements a **traceback algorithm** for sequence alignment, reconstructing the optimal path through an alignment matrix.
+
+## Core Functionality
+
+- **Input**:  
+  - `pathMatrix`: Encodes alignment decisions (match/mismatch/gap) as integers.  
+  - `lseqA`, `lseqB`: Lengths of sequences A and B.  
+  - `path`: Pre-allocated slice to store the traceback path.
+
+- **Output**: A compact representation of alignment steps, alternating between:
+  - Diagonal moves (`ldiag`): Matches/mismatches (one step in both sequences).
+  - Horizontal/vertical moves (`lleft` or `lup`): Gaps in sequence B (horizontal) or A (vertical).
+
+## Algorithm Highlights
+
+- **Reverse traversal** from `(lseqA−1, lseqB−1)` to origin.
+- **Batching logic**: Consecutive gaps in same direction are aggregated (e.g., `lleft += step`) to compress run-length encoding.
+- **Path reconstruction**: Steps are pushed *backwards* into the `path` slice using a moving pointer `p`.
+- **Memory efficiency**: Uses `slices.Grow()` to preallocate space and logs resizing for debugging.
+
+## Encoded Path Semantics
+
+Each pair in the returned slice encodes:
+- `[diag_count, move_type]`, where `move_type` is either a gap length (`lleft > 0`: horizontal, or `lup < 0`: vertical) or zero (end of diagonal run).
+
+## Use Case
+
+Enables efficient reconstruction and serialization of alignment paths—ideal for tools requiring low-level control over dynamic programming backtracking (e.g., pairwise aligners, edit-distance decompositions).