TestLink

I have a unique issue with testlink and haven't been able to find help in the user manuals or other threads.

Our company uses an Agile software life cycle model. So test cases run against a particular build need not be run again for the next build release as there is no new code added to an existing feature.
When i add a test case to a test plan, it will show against all builds. There is no way to assign it only to a particular build number

When test cases are assigned to a certain build and you have already passed or failed it, you can still see the same test case when you are executing the test plan for the next build; but it will show up as "not run" by default.

1) How can I configure testlink so that i can only see the test cases that have not been executed in the previous build or that have been failed so I can re-run it. If it already passed then It should not show up in my list.
OR
2) Can the result of the test case run in a particular build be copied to the next build only if it is marked as 'PASS' ?

This would save us a lot of time

TL uses test plan+platforms to create N sets of test case to be executed. Builds are used during execution, and can be used to assign testers to different test cases in (test plan, platform). The features you request are not present on TestLink.
One (not complete solution) may be is create a test plan for each sprint. Standard reports are done at Test Plan level => you will not be able to create a report with result from multiple test plans (if your choice is one test plan for sprint).
When Tester Assignment was refactored to add to (test plan,platform) build, idea was that test cases that has NOT TO BE RUN on a BUILD will remain WITHOUT TESTER ASSIGNED (unassigned). May be this can help you.

Thank you!! This will definitely help.