fix(scripts): stop license checks failing on valid headers

[chethanuk]

Description

make license-check fails intermittently on files whose headers are correct, naming a different file each run.

Both license scripts test the header with echo "$header" | grep -q .... grep -q exits the moment it matches, so echo can lose the race on the write end and die of SIGPIPE (141). Both scripts run under set -o pipefail, which promotes that 141 to the pipeline's status, and ! pipeline then reads a header that is plainly present as missing.

Measured on internal/llmloop/compression.go — a 410-byte header, far under the 64KiB pipe buffer — with the CPU saturated: 4 spurious failures in 3000 iterations of the SPDX pipeline alone. End to end under the same load, verify-license.sh failed 5 of 10 runs on current main and 0 of 10 with this change.

has_header() in add-license.sh has the identical race, and there it is worse than a flake. A false negative makes add_header() prepend a second copyright block to a file that already has one — which is the duplicate SPDX header that had to be removed from internal/config/testconnection/testconnection.go during review of #605.

Feeding the header through a here-string removes the second process, so nothing is left to receive SIGPIPE. The year lookup was a grep | grep | head -1 chain carrying the same exposure (head -1 exits after one line), so it now uses bash's own regex match and spawns nothing.

Limitation

This ships without a test. Reproducing the race takes thousands of iterations under CPU saturation, so the test would become the flake it is meant to prevent. The fix is structural rather than probabilistic: with no second process in the pipeline, there is no SIGPIPE to deliver.

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Refactoring (no functional changes)
• Documentation update
• CI / Build / Tooling

How Has This Been Tested?

• make test passes locally
• Manual testing (describe below)

make check and make test both pass on current main.

• Year parity: the new [[ =~ ]] match against the old grep | grep | head -1 chain over 7 inputs, including a 5-digit year, a CopyrightX near-miss, no match at all, and two Copyright lines in one header. Identical results on all 7.
• Detection is unchanged, checked against a staged probe file: missing SPDX reports (missing SPDX identifier), year 1999 reports (invalid year: 1999), year 2099 reports (invalid year: 2099).
• make license-add run twice over a header-less file leaves exactly one SPDX-License-Identifier line, and the tree is unchanged on a fully-licensed checkout.
• Both scripts stay pure ASCII, as they are on main.

Checklist

• My code follows the project's coding style (go fmt, go vet)
• I have performed a self-review of my code
• I have added tests that prove my fix is effective or my feature works
• New and existing unit tests pass locally with my changes
• I have updated the documentation accordingly (if applicable)
• I have signed the CLA

See the Limitation note above on why no test is included.

Related Issues

None open for this; found while rebasing unrelated PRs, where license-check failed on files those branches never touched.

[github-actions]

✅ OpenCodeReview: Review complete: 0 finding(s) across 2 selected item(s).

[lizhengfeng101]

LGTM