DECISION NEEDED: ternary packing layout is arithmetically impossible (blocks 343 of 906 corpus files)

docs/now/2026-09-23-published-decision-needed-ternary-packing-layout-is-arithmetically-imp.md

@@ -0,0 +1,11 @@
+# NOW -- DECISION NEEDED: ternary packing layout is arithmetically impossible (blocks 343 of 906 corpus files) (published 2026-09-23)
+
+## A bee's work on #3873, published from `queen-3873` (Closes #3873)
+
+- The branch changes 1 file(s): `specs/base/types.t27`.
+- `git diff --stat origin/master...queen-3873` reads: 1 file changed, 10 insertions(+), 6 deletions(-)
+- This entry is written by the publisher, not by the bee. A pull request must
+  add exactly one `docs/now/` entry and a bee has no way to know that: its brief
+  names a boundary file and acceptance criteria, and `docs/now/` is neither.
+- What this entry does NOT establish: that the work is correct. The gates on the
+  pull request judge that, and they are the same gates every other change meets.

specs/base/types.t27

@@ -24,12 +24,12 @@ pub const Trit = enum(i8) {
 // Constants - PackedTrit
 // ============================================================================
 
-// PackedTrit: 8 trits packed into u8
-// Layout: [t7 t6 t5 t4 t3 t2 t1 t0] where each t ∈ {-1, 0, +1}
+// PackedTrit: 4 trits packed into u8
+// Layout: [t3 t2 t1 t0] where each t ∈ {-1, 0, +1}
 // Encoding: -1 → 10, 0 → 00, +1 → 01 (2 bits per trit)
-// So packed byte: [t7_1 t7_0][t6_1 t6_0]...[t0_1 t0_0]
+// So packed byte: [t3_1 t3_0][t2_1 t2_0][t1_1 t1_0][t0_1 t0_0]
 pub const PACKED_BITS_PER_TRIT : u8 = 2;
-pub const TRITS_PER_BYTE : u8 = 8;
+pub const TRITS_PER_BYTE : u8 = 4;
 
 // Trit value mapping (2-bit to trit)
 // -1 → 10b = 2, 0 → 00b = 0, +1 → 01b = 1
@@ -48,7 +48,7 @@ pub const PackedTrit = u8;  // Type alias
 // Can represent any value in 3^27 ≈ 7.6×10^12 states
 // Practical use: vector operations, VSA bindings, weight storage
 pub const TRITS_PER_WORD : u8 = 27;
-pub const WORD_BYTES : u8 = 5;   // ceil(27/8) = 5 bytes for 27 trits
+pub const WORD_BYTES : u8 = 7;   // ceil(27/4) = 7 bytes for 27 trits
 
 pub const TernaryWord = [WORD_BYTES]u8;  // Type alias
 
@@ -199,7 +199,11 @@ pub fn ternary_word_pack(src: []Trit, count: u8) TernaryWord {
     var result = [_]u8{0} ** WORD_BYTES;
 
     for (0..@min(count, TRITS_PER_WORD)) |i| {
-        result = pack_trit(src[i], @intCast(i), result);
+        const byte_index = i / TRITS_PER_BYTE;
+        const trit_in_byte = i % TRITS_PER_BYTE;
+        const old = result[byte_index];
+        const packed = pack_trit(src[i], trit_in_byte, old);
+        result[byte_index] = packed;
     }
 
     return result;