Diagnose: ownership rules not assigning issues

# Diagnose: ownership rules not assigning issues

## Step 1: check the syntax

Rules are `type:pattern owners`, one per line:

```
path:src/backend/* #backend-team
path:src/api/* #api-team
```

Patterns are unix globs (`*`, `?`), not regex. A rule written as regex (`path:src/backend/.*`) matches nothing. Owners are emails or `#team` names separated by spaces.

## Step 2: check what the rule matches against

`path` matches file paths in stack traces, which are build-output paths, not repo paths. If you build into `dist/`, the stack trace says `dist/...` while your rule says `src/...`. Either write rules against the built paths or set up code mappings so Sentry normalizes them. The issue details page has an ownership editor showing suggested paths from the actual event: use those suggestions instead of guessing.

## Step 3: check precedence and one-shot behavior

Ownership rules beat CODEOWNERS. And once an issue is assigned (manually or automatically), auto-assignment turns off for that issue. If someone assigned it by hand during triage, the rules will never reassign it. Unassign it to let automation take over again.

## Step 4: CODEOWNERS specifics

CODEOWNERS import needs code mappings configured first, plus external team/user mappings (source-control identities to Sentry users/teams); rules without mappings are silently ignored. The file caps at 3MB. Also note the scope: ownership only applies to error issues, not performance or replay issues. If those go unassigned, that is by design.

## Verify

Create a test issue with a stack frame matching a rule path and confirm assignment within a minute. For CODEOWNERS, confirm the team mapping resolves: an unmapped team name fails silently.