JQL parser inconsistency - escaped square brackets \\[ \\] inside double-quoted strings fail

[Tripti Singh]

Square brackets escaped as \\[ and \\] inside double-quoted JQL string values
cause 0 results on some Jira Cloud instances, while other instances silently
strip the backslashes and return correct results.

## Steps to Reproduce
1. Have an issue type containing square brackets, e.g. "[System] Incident"
2. Run JQL:
project = 'AB5' and "issuetype" = "\\[System\\] Incident" order by id
3. On some Cloud instances: returns 0 results
4. On other Cloud instances: returns correct results (backslashes are ignored)

## Actual Behavior

- Some instances (strict parser): "\\[System\\] Incident" matches nothing
- Other instances (lenient parser): "\\[System\\] Incident" is treated as "[System] Incident" and works

## Environment
- Jira Cloud (newer /rest/api/latest/search/jql endpoint)

## Question

1. Are [ and ] officially reserved characters that require escaping inside
double-quoted JQL string values? They are not listed in the documented
reserved characters list.

2. Is this a known bug — the inconsistent parsing behavior across Jira Cloud
instances where escaped \\[  \\] works on some but returns 0 results on others?

3. We have removed the escaping of [ and ] from our JQL queries (i.e., we now
send "[System] Incident" instead of "\\[System\\] Incident" in quoted strings).
Will unescaped square brackets inside double-quoted values cause any issues
on any Jira Cloud instance?

[Arkadiusz Wroblewski]

Hello @Tripti Singh 

The reason one Cloud site accepts the backslashes while another returns zero results comes down to inconsistent parser leniency across different site versions. You shouldn't rely on that lenient behavior, as Jira's parser can interpret those backslashes differently depending on backend updates.

Dropping the bracket escaping for exact matches is definitely the right move here.