[kholdrex]

merge() adds the named destinations of the appended document one at a time. For each one it checks title in names and then add_named_destination_array() scans the array again to find where to insert, so a document with many named destinations takes quadratic time.

For documents with at least 32 named destinations, the string entries now go into a set for the lookup. If the existing keys are sorted, the new destinations are collected and sorted into the array once at the end. Putting each one before the first greater key, as add_named_destination_array() does, gives the same order as that stable sort. Arrays with unsorted keys still use the old insertion, and documents with fewer destinations keep the old code, since building the index reads the whole array.

writer.append(reader) with all destinations on one page:

Named destinations	main	this PR
2,000	0.24 s	0.04 s
4,000	0.88 s	0.07 s
8,000	3.3 s	0.19 s

The resulting /Names arrays and written files are the same as on main in about 1,300 generated cases (unsorted and odd-length arrays, indirect arrays, byte string keys, clone_from writers, appending the same file twice), and appending many small documents into a large array is as fast as before.

AI assistance: Claude Code (Claude Opus 5.5) helped write and measure this, and Codex (GPT-6 Astra) reviewed it. I reviewed the change and ran the test suite.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.81%. Comparing base (f5b3f07) to head (8178a59).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4360   +/-   ##
=======================================
  Coverage   98.81%   98.81%           
=======================================
  Files          59       59           
  Lines       12139    12197   +58     
  Branches     2310     2318    +8     
=======================================
+ Hits        11995    12053   +58     
  Misses         70       70           
  Partials       74       74           

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.