docs(pcs): the cap dump's trailing bits are don't-care

Mirrors CrispEmbed 75b1cf53 into both copies (test-copies-in-sync requires it).

The truecase head always emits 16 bits, but the reconstruction reads bit `c`
only for character `c` of the piece — the tail is padding the model fills
arbitrarily. A consumer comparing all 16 will fail a CORRECT artifact: the
q4_k-imatrix build differs from the f32 reference on bits 4..12 of `▁ok` (3
characters) while producing byte-identical text. CrispEmbed's pcs_parity.py did
exactly that until it was truncated to the piece length, so the note is worth
carrying next to the dump rather than only in the consumer.

Comment-only; verified test-copies-in-sync 47/47 and format.sh OK on 583 files.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: crispasr integration

crisp_punc/src/pcs.cpp

@@ -837,8 +837,13 @@ static PCSResult pcs_run(pcs_context& ctx, const std::vector<int>& token_ids) {
         // Two ints per token: thresholded boundary, then the hard argmax.
         dump("PCS_DUMP_SEG",
              [&](FILE* fp, int t) { fprintf(fp, "%d %d", result.sbd_preds[t] ? 1 : 0, seg_argmax[t] ? 1 : 0); });
-        // 16 bits per token, MSB-first by character position — the truecase head
-        // is per-CHARACTER within the token, not one flag per token.
+        // 16 bits per token, by character position — the truecase head is
+        // per-CHARACTER within the token, not one flag per token. ⚠ Only the
+        // first `len(piece)` bits are meaningful; the reconstruction reads bit
+        // c for character c and never looks further, so the tail is padding the
+        // model fills arbitrarily and a consumer MUST truncate before comparing.
+        // Comparing all 16 fails a correct artifact (see CrispEmbed
+        // tests/pcs_parity.py, which did exactly that until it was fixed).
         dump("PCS_DUMP_CAP", [&](FILE* fp, int t) {
             for (size_t c = 0; c < result.cap_preds[t].size(); c++) {
                 fputc(result.cap_preds[t][c] ? '1' : '0', fp);

src/pcs.cpp

@@ -837,8 +837,13 @@ static PCSResult pcs_run(pcs_context& ctx, const std::vector<int>& token_ids) {
         // Two ints per token: thresholded boundary, then the hard argmax.
         dump("PCS_DUMP_SEG",
              [&](FILE* fp, int t) { fprintf(fp, "%d %d", result.sbd_preds[t] ? 1 : 0, seg_argmax[t] ? 1 : 0); });
-        // 16 bits per token, MSB-first by character position — the truecase head
-        // is per-CHARACTER within the token, not one flag per token.
+        // 16 bits per token, by character position — the truecase head is
+        // per-CHARACTER within the token, not one flag per token. ⚠ Only the
+        // first `len(piece)` bits are meaningful; the reconstruction reads bit
+        // c for character c and never looks further, so the tail is padding the
+        // model fills arbitrarily and a consumer MUST truncate before comparing.
+        // Comparing all 16 fails a correct artifact (see CrispEmbed
+        // tests/pcs_parity.py, which did exactly that until it was fixed).
         dump("PCS_DUMP_CAP", [&](FILE* fp, int t) {
             for (size_t c = 0; c < result.cap_preds[t].size(); c++) {
                 fputc(result.cap_preds[t][c] ? '1' : '0', fp);