[mhutchinson]

C2SP specs (tlog-proof@v1, tlog-checkpoint, tlog-cosignature, and tlog-policy) define decimal integers as base-10 representations without leading zeros (except for 0 itself), with tlog-proof leaf indices bounded to 0..2^63-1 and tlog-policy group thresholds bounded to 1..n (with n >= 1).

Previously:

• proof.TLogProof.Unmarshal used strconv.ParseUint(idxStr, 10, 64), accepting leading zeros (e.g. 007) and indices >= 2^63.
• log.Checkpoint.Unmarshal and note.formatRFC6962STH accepted leading zeros on the checkpoint tree size line.
• policy.TLogPolicy.Unmarshal and witness.ParsePolicy accepted leading zeros on numeric group thresholds.
• witness.ParsePolicy accepted group thresholds of 0 and groups with 0 members, producing a Group{N: 0} that trivially satisfied any checkpoint.

Reject leading zeros across all decimal integer parsers, bound tlog-proof leaf indices to 63 bits, and require group thresholds in witness.ParsePolicy to satisfy 1 <= k <= n with at least one member.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.44%. Comparing base (fa00c16) to head (6818d47).
⚠️ Report is 203 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #293      +/-   ##
==========================================
+ Coverage   82.57%   90.44%   +7.87%     
==========================================
  Files           5       10       +5     
  Lines         241     1057     +816     
==========================================
+ Hits          199      956     +757     
- Misses         30      101      +71     
+ Partials       12        0      -12     

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