fix: truncate each tag individually in multi-tag templates

[nookyo]

Summary

Fix incorrect tag truncation in metadata-action when default-template produces multiple comma-separated tags. Previously, the entire rendered string was truncated as a single value, which caused trailing tags (e.g. {{short-sha}}) to be silently dropped. Now each tag is truncated independently.

Issue

Fixes #654

Breaking Change?

• Yes
• No

Scope / Project

actions/metadata-action

Implementation Notes

The root cause was in src/index.js: after fillTemplate() renders the template string, the result was passed directly to truncateTag() as one string. For a template like:

"{{ref-name}}-{{timestamp}}, {{ref-name}}-{{short-sha}}, {{ref-name}}, {{short-sha}}"

this produced a 155-char string that got sliced to 128, cutting off the last tags entirely.

Fix: split the rendered string by ,, trim each part, truncate each tag individually to tag-max-length, then rejoin with ", ". Extra tags (from extra-tags input) were already handled per-tag and required no changes.

Documentation in README.md updated to reflect the new per-tag truncation behavior, including an example from the original bug report.

Tests / Evidence

New integration test added in tests/integration.index.render.test.js:

"should truncate each tag individually when template contains multiple comma-separated tags"

Simulates a long branch name (fix-increase-integration-tests-memory) with template producing 4 comma-separated tags. Asserts:

• Every individual tag is ≤ 128 characters
• The {{short-sha}} tag (11 chars) is present and correct in the output

All 35 tests pass:

Test Suites: 5 passed, 5 total
Tests:       35 passed, 35 total

Additional Notes

The fix is backward-compatible - single-tag templates behave identically to before (split by , produces one element, truncated as usual).