[jaeyeom]

Summary

Resolves #397

• searchAuthoredTickets marked every ticket in a multi-ticket chunk unknown when that chunk mapped no PR, even if another chunk in the same run had already mapped one. UntrustedCloseReason then refused --close-merged for the whole set, including tabs already classified merged.
• The sweep is unknown only when no chunk mapped a PR and more than one ticket was searched. An empty chunk is no_pr when another chunk mapped a result. A fully empty multi-ticket sweep still warns and stays unknown.
• The unknown bucket in devtools/prsync/README.org matches that rule.

Demo

Before, six PR-less tickets in the first search chunk and a merged ticket in the next:

search "AP-1 OR AP-2 OR AP-3 OR AP-4 OR AP-5 OR AP-6" returned no matching PRs for any of 6 tickets; treating as unknown
close-merged refused: search classification is unknown

After, those six are no_pr, the merged ticket stays merged, and there is no unknown warning, so --close-merged can close it. Two chunks that both map nothing stay unknown, with one warning per chunk.

Test plan

• TestOrphansEmptyChunkIsNoPRWhenAnotherChunkMapped failed first with warnings = [search "AP-1 OR AP-2 OR AP-3 OR AP-4 OR AP-5 OR AP-6" returned no matching PRs for any of 6 tickets; treating as unknown], then passed (bazel test //devtools/prsync/internal/scan:go_default_test --test_filter='TestOrphansEmptyChunkIsNoPRWhenAnotherChunkMapped|TestOrphansAllEmptyMultiChunksStayUnknown|TestOrphansChunksWhenOverFiveOROperators|TestOrphansEmptySweepIsUnknownNotNoPR' --test_output=all --test_arg=-test.v)
• That same run passed TestOrphansAllEmptyMultiChunksStayUnknown, TestOrphansChunksWhenOverFiveOROperators, and TestOrphansEmptySweepIsUnknownNotNoPR
• go test ./devtools/prsync/... passed
• GOPACKAGESDRIVER= golangci-lint run ./devtools/prsync/internal/scan/... reported 0 issues, and golangci-lint run ./... during make check reported 0 issues
• make check-semgrep, make check-bazel-go-files, and make check-org-lint-tests passed (semgrep: 647 rules, 0 findings)
• make check is green

make check failed in oserrorsgodernize on four existing os.IsNotExist diagnostics in devtools/setup-dev/ansible/packages_data_test.go (lines 986, 1001, 1016, and 1154). Those are the diagnostics recorded on #396. check-semgrep, check-bazel-go-files, and check-org-lint-tests did not run inside that make check because lint-golangci stopped it. They were run separately and passed. bazel test //... reported 330 tests passed.

Reviewer notes

This is the first option in #397: trust the sweep per run. UntrustedCloseReason is unchanged. A merged tab is no longer paired with unknown from an empty sibling chunk, so the close proceeds. A sweep that maps nothing is still refused.