fix: Old-format CIDs are warned but still silently dropped from the pool (#801)

- Change WARNING to explicitly state "legacy CID format ... migration not supported, skipping"
- Expand comment near the startswith('candidate_') guard to document the CID format
  contract and explain why re-admission is intentionally out of scope (no surviving
  generation_N.jsonl files from runs 1-6 exist in the repo)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tools/push3-evolution/evolve.sh

@@ -819,9 +819,14 @@ for fname in sorted(os.listdir(output_dir)):
                     continue
                 # Canonical CID format is "candidate_XXX" (zero-padded numeric suffix,
                 # e.g. "candidate_001"); gen_idx is derived from the enclosing filename.
-                # Old runs 1–6 used "gen{N}_c{MMM}" — see manifest.jsonl schema (#720).
+                # Old runs 1–6 used "gen{N}_c{MMM}" — that format is intentionally not
+                # re-admitted: no surviving generation_N.jsonl files from those runs exist
+                # in the repo, so migration is out of scope.  Any entry that does not match
+                # "candidate_" is skipped permanently.
                 if not cid.startswith('candidate_'):
-                    print(f'WARNING: skipping unrecognised CID format {cid!r} in {fname}')
+                    print(f'WARNING: legacy CID format {cid!r} in {fname} '
+                          f'(gen{{N}}_c{{MMM}} from runs 1-6) — '
+                          f'migration not supported, skipping')
                     continue
                 cand_str  = cid[len('candidate_'):]      # numeric suffix, e.g. "001"
                 push3_path = os.path.join(