feat(source/kafka): cold-group seek/lag, typed start-offset option, honest vendor-boundary docs - #200
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…onest vendor-boundary docs P1-4: SeekToStart/SeekToEnd/SeekToTime enumerated partitions from committed offsets only, so a fresh group (nothing committed) silently no-oped. Partition discovery now falls back to a kmsg MetadataRequest for any consume topic without commits; Lag keeps the committed baseline but reports an error (exported ErrNoCommittedOffsets sentinel) instead of a misleading 0 for a cold group, and excludes never-committed partitions. P1-5: WithStartOffset(kafka.StartEarliest|StartLatest) maps onto kgo.ConsumeStartOffset for brand-new groups (default earliest = franz-go default); committed partitions always resume from their commit. Cold-start posture documented in package doc and README. P1-3: 'No franz-go type appears in an exported signature' corrected to the real boundary in kafka.go package doc and README: the neutral Inlet/ Subscription/Message seam is vendor-free; WithSASL/WithBalancer/ WithClientOptions/WithClient deliberately expose franz-go types as power seams. Core Seekable/LagReporter doc comments updated to match backend behavior. Tests: cold-group seek discovery, committed-vs-metadata partition selection, mixed-topic coverage, Lag cold-group sentinel + partial-commit counting, metadata error propagation, WithStartOffset mapping.
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Checkpoint 2/5 — P1 fixes on the road to source/v1.0.0
Stacked on #199 (checkpoint 1).
P1-4 — cold-group Seek/Lag silently no-oping
SeekToStart/End/Timebuilt requests purely fromCommittedOffsets(); a fresh group got an empty request and succeeded while doing nothing. NowassignedPartitionsenumerates committed offsets per topic where present and falls back to broker metadata (kmsg.MetadataRequest) for topics without commits — seeks always act.Lagneeds a committed baseline: it now returns exportedErrNoCommittedOffsets(errors.Is-matchable) for a cold group instead of0, nil, and counts only partitions with commits (documented).P1-5 — initial start-offset policy exposed + documented
New
WithStartOffset(kafka.StartEarliest | kafka.StartLatest)mapping tokgo.ConsumeStartOffset; default stays earliest (franz-go's default), committed partitions always resume from commit regardless. Cold-start posture documented in the package doc (# Cold start) and README (## Cold start).P1-3 — false vendor-free claim corrected
"No franz-go type appears in an exported signature" was false. Rewritten to the real boundary in both
kafka.gopackage doc and README: neutral seam vendor-free;WithSASL/WithBalancer/WithClientOptions/WithClientare deliberate typed power seams. CoreSeekable/LagReporterdocs updated to describe actual enumeration/baseline semantics.Evidence (run locally on this branch)
GOWORK=off go build ./... && go vet ./... && go test -race -count=1 ./...go vet ./... && go test -race -count=1 . ./memsourceNew tests (all pass under
-race -count=1):TestSeekToStartColdGroupDiscoversPartitions,TestSeekToEndUsesCommittedWhenPresent,TestSeekToTimeColdGroupMixedTopics,TestLagColdGroupErrorsWithSentinel,TestLagPartialCommitsCountOnlyCommitted,TestTopicPartitionsErrorPropagates,TestWithStartOffsetOptionConfigAndMapping.Regressions vs baseline: none (full suites green). API diff vs review-approved list: adds only
WithStartOffset,StartOffset+StartEarliest/StartLatestconstants, andErrNoCommittedOffsetssentinel — all required by approved P1 fixes.