DD: refactor finishMoveKeys and finishMoveShards into focused helpers

[saintstack]

Both functions grew past 400-500 lines of a single deeply-nested try/loop. Extract the four sequential phases each performs — decode planning snapshot, build dest SS interfaces, wait outside a transaction for destination readiness, re-verify and commit — into standalone helpers so the top-level functions read as orchestration loops.

finishMoveKeys (~440 → ~180 lines) delegates to:

• DecodedKeyServersState + decodeKeyServersState() — two-pass keyServers validation with the empty-dest / subset-of-team tolerance from the planning loop; returns nullopt when the iteration's range is already fully moved.
• buildKeysDestServerInterfaces() — reads serverList entries and returns (interfaces, read version) so the caller can drop the txn before the long wait.
• waitForKeysDestServers() — issues waitForShardReady() for SSes and TSSes, applies the counter-based TSS ignore policy, returns the ready count.
• reverifyKeysDestAndCommit() — post-wait re-read, KRM-boundary re-truncation, destUnchanged() check, keyServers/serverKeys writes, commit. Returns false on dest change so the caller retries via the existing retryAfterPostWaitChange().

finishMoveShards (~525 → ~271 lines) delegates to shards-specific analogs (the two flavors' TSS policy, dest-decode invariants, and post-wait writes differ enough that forcing shared code hurts readability):

• DecodedShardsKeyServers + decodeAndPreCheckShards() — dataMoveId stamp check on every sub-range and the per-sub-range AUDIT_DATAMOVE_PRE_CHECK (coroutine because of the audit call). Throws retry() and sets cancelDataMove on stamp mismatch, matching prior behavior.
• buildShardsDestServerInterfaces() — like the keys flavor but throws retry() on missing serverList entries rather than asserting, matching the pre-refactor shards code.
• waitForShardsDestServers() — implements the time-based skipTss latch (all SSes ready for DD_WAIT_TSS_DATA_MOVE_DELAY without TSS catching up → skip TSS for the remainder of the move).
• ReverifyShardsResult (enum) + reverifyShardsAndCommit() — handles all three concurrent-change branches (dataMove deleted / phase changed / dest changed) uniformly via retryAfterPostWaitChange(), plus KRM re-truncation, bulk-load task completion, partial-vs-full commit, and dataMove metadata clear. Returns {RetryLoop, PartialCommitted, FullyCommitted} so the outer loop can distinguish "keep going on the same move" from "move complete".

Pure refactor: no behavior change intended. Every CODE_PROBE, TraceEvent, ASSERT, error-code branch, and control-flow decision from the current finishMoveKeys / finishMoveShards on origin/main is preserved — including the newer post-#13364 machinery (retryAfterPostWaitChange, KRM boundary re-truncation with rare probes, ASSERT rereadEnd <= end, per-iteration FlowLock take/release). The catch handlers, backoff paths, and retry-cap semantics are untouched.

Two joshua runs back-to-back:

20260701-195314-stack-refactor-8d063fe367fe89d0 compressed=True data_size=37315233 duration=2111916 ended=100000 fail_fast=10 max_runs=100000 pass=100000 priority=100 remaining=0 runtime=0:33:10 sanity=False started=100000 stopped=20260701-202624 submitted=20260701-195314 timeout=5400 username=stack-refactor
20260701-211819-stack-refactor2-dbca4f2c3122dcd3 compressed=True data_size=37316315 duration=2610790 ended=100000 fail_fast=10 max_runs=100000 pass=100000 priority=100 remaining=0 runtime=0:41:54 sanity=False started=100000 stopped=20260701-220013 submitted=20260701-211819 timeout=5400 username=stack-refactor2

Code review
review-findings.md

(This PR includes attention for item #2 in the review-findings.md list)

[foundationdb-ci]

Result of foundationdb-pr-clang-ide on Linux RHEL 9

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• Duration 0:21:52
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[foundationdb-ci]

Result of foundationdb-pr-macos-m1 on macOS 14.x

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[foundationdb-ci]

Result of foundationdb-pr-clang on Linux RHEL 9

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[foundationdb-ci]

Result of foundationdb-pr-clang-arm on Linux RHEL 9

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[foundationdb-ci]

Result of foundationdb-pr-macos on macOS 14.x

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[foundationdb-ci]

Result of foundationdb-pr on Linux RHEL 9

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[foundationdb-ci]

Result of foundationdb-pr-cluster-tests on Linux RHEL 9

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• Duration 1:02:52
• Result: ✅ SUCCEEDED
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