fix: cap block header count parameter

[tolga-tom-nook]

Fixes an impossible block-header count guard in api/views/headers.py.

The previous condition used count < 1 and count > 2000, which can never be true. As a result, /rest/block/headers/{block_pointer}/0, negative counts, and very large counts bypassed the intended default/cap behavior and were passed through to the model layer.

This PR changes the guard to count < 1 or count > 2000 and now includes focused regression coverage for:

• count=0, count=-1, and count=5000 defaulting to the safe 2000-header bound;
• non-numeric count returning the existing parameter error without a model call;
• valid in-range counts continuing to call the model unchanged.

Bounty context / claim:

• Bitgesell contribution bounty: BGL PR bounty hunt ($10000 overall budget) bitgesell#39
• Bitgesell broader contribution budget: BGL (Bitgesell) Bounty/Improvement Program ($50000 budget) bitgesell#81
• Requested liquid payout rail if accepted: USDT / USDC-compatible EVM address 0x4a76c7E64C08cF29B59eFC640b4ada97A270d428

Validation:

• python3 -m py_compile api/views/headers.py test/pytest/blocks_data/test_block_headers_count_validation_unit.py
• python3 -m pytest -q --confcutdir=test/pytest/blocks_data test/pytest/blocks_data/test_block_headers_count_validation_unit.py → 3 passed
• git diff --check

---

Executor refresh — 2026-06-17T08:57:30Z

Revalidated payout-readiness for the Bitgesell #81/#39 direct-USDT candidate:

• GitHub live check: PR remains open/authored by tolga-tom-nook, MERGEABLE / CLEAN; no maintainer requested-changes review found.
• Local validation: python3 -m py_compile api/views/headers.py test/pytest/blocks_data/test_block_headers_count_validation_unit.py passed.
• Local validation: python3 -m pytest -q --confcutdir=test/pytest/blocks_data test/pytest/blocks_data/test_block_headers_count_validation_unit.py passed (3 passed).
• Local validation: git diff --check origin/master...HEAD passed.
• Branch remains current enough for review: git rev-list --left-right --count origin/master...HEAD = 0 2.

Evidence: /home/ubuntu/tom-agent/opportunity-os/evidence_bundle/bitgesell_bglapiserver_pr8_revalidation_20260617T085730Z/summary.md

[MyTH-zyxeon]

Maintainers - this looks like a narrow, reviewer-friendly bounty slice for the Bitgesell improvement program.

What seems concretely useful here:

• Root cause is explicit and easy to validate: count < 1 and count > 2000 can never trigger, so invalid / oversized header counts leak through instead of collapsing to the intended safe bound.
• Patch scope stays tight: request validation + regression coverage, without broad API or model-layer changes.
• The acceptance surface is small enough to review quickly.

Suggested acceptance checks:

1. /rest/block/headers/{block_pointer}/0 no longer passes 0 through and returns the bounded/default behavior instead.
2. oversized values like 5000 are capped the same way.
3. existing normal in-range requests still behave unchanged.
4. negative / malformed path values still follow the repo's existing error-handling path rather than introducing a new behavior contract by accident.

If you want a different cap/default behavior than 2000, calling that out here should let the author adjust without broadening the PR.