hg log output merging obscures individual commits for screen readers

Problem

The default hg log output uses temporal indentation and line wrapping that causes consecutive commit messages to be read as a single block by screen‑reader users, making it difficult to identify and navigate individual revision entries.

Likely Explanation

Screen readers linearize text output; without a clear boundary between commits, the announcements run together. Adding a single, unique delimiter line before each revision header creates an audible cue that a new commit begins, while leaving the existing plain‑text structure intact.

Confirmed Facts from Research

• A delimiter line (e.g., === HG LOG ENTRY ===) placed immediately before the revision header preserves the current command‑line signature and does not require new mandatory flags.
• Regex‑based parsers can ignore or consume the delimiter line, maintaining compatibility with existing automation tools.
• The delimiter must be a string that never appears in commit messages to avoid false positives.
• If a user disables the delimiter via an environment variable or configuration option (e.g., ui.log-delimiter=false), the output reverts to the original format, satisfying the graceful‑degradation constraint.

Recommendation

1. Introduce an optional configuration setting (e.g., ui.log-delimiter) that, when enabled, inserts the delimiter line before each commit entry.
2. Keep the default off to preserve backward compatibility for scripts that depend on exact line counts.
3. Document the delimiter string and its purpose so that parser authors can optionally handle it.
4. Defer a full JSON output mode (--output=accessible) to a separate enhancement; the delimiter approach addresses the immediate accessibility need with minimal risk.

Verification Steps

1. Run hg log with the delimiter enabled and compare output length; ensure scripts that extract the revision hash from the first line of each entry still succeed.
2. Feed the new output to a screen reader (NVDA, VoiceOver) and verify that each delimiter triggers a distinct commit announcement.
3. Test Mercurial's own log‑parsing utilities and popular third‑party tools (e.g., hgview) to confirm they still identify revision headers correctly.

Open Diagnostic Detail

If any downstream tooling is known to break on extra blank or non‑standard lines, please report the specific parser and its line‑count assumptions. That single detail would determine whether the default should remain off or can be safely flipped on.