docs: add post-v2.1.0 fixes to CHANGELOG [Unreleased] before release preparation #555

Goal

Make the [Unreleased] changelog section complete so the v2.2.0 release-preparation PR can move it into the dated section and the generated release notes are accurate.

Background

docs/release-process.md makes the changelog the source for release notes. #550 recorded the post-v2.1.0 changes, but the section has no entry that mentions several user-visible fixes merged since v2.1.0 (git log v2.1.0..origin/main):

• fix: preserve literal PATH entries during deduplication #547 preserve literal PATH entries during deduplication (base_std_* PATH helpers)
• fix: reject non-root git update paths #544 reject non-root Git update paths (lib_git.sh)
• fix: preserve exact string and list semantics under nocasematch #543 preserve exact string and list semantics under nocasematch
• fix: validate integer range before arithmetic #545 validate integer range before arithmetic

Entries for #546 (completion traversal) and the CI items (#538, #539) are present, which suggests the others were missed or merged after the section was written.

Scope

• Review git log v2.1.0..origin/main against CHANGELOG.md [Unreleased] and add missing user-visible entries under Fixed/Changed/Security.
• Re-check immediately before release preparation, since merges continue (ci: add fail-closed validation aggregates #551 and others).

Acceptance Criteria

• Each user-visible merged change since v2.1.0 appears in [Unreleased] (or is explicitly judged internal).
• Wording follows the existing section style; no behavior is described that was not merged.
• tests/changelog-guard.sh and ./tests/validate.sh pass.

Validation

Compare git log --oneline v2.1.0..origin/main with the changelog; run ./tests/validate.sh.

Project Fields

• Status: Backlog
• Priority: P2
• Area: Docs
• Size: S
• Issue type: Task
• Assignee: codeforester
• Milestone: v2.2.0

Agent Assignment

Assignee: @codeforester. Found during the pre-release documentation walkthrough of 2026-10-07 at the origin/main heads of base-bash-libs (454aabc) and base-bash-libs-demo (5e598be). No repository content was changed by the review.