fix(file-service): 400 on revoke of an unknown email

[gupta-sahil01]

What changes were proposed in this PR?

ResourceAccess.revoke dereferenced the result of UserDao.fetchOneByEmail(email) without a null check:

val granteeUid = new UserDao(ctx.configuration()).fetchOneByEmail(email).getUid

fetchOneByEmail returns null for an address with no account, so revoking a dataset or model share for an unregistered email threw a NullPointerException. The service registers no ExceptionMapper for it, so it surfaced as an opaque HTTP 500 rather than an actionable 400.

grant, in the same object, already performed the correct check. This PR extracts that check into a private resolveUidByEmail helper and routes both grant and revoke through it, mirroring ComputingUnitAccessResource.resolveUidByEmail added in #6446 for the same defect.

Affected endpoints:

• DELETE /api/access/dataset/revoke/{did}/{email}
• DELETE /api/access/model/revoke/{mid}/{email}

Behaviour note: revoke now also rejects placeholder accounts, matching grant and ComputingUnitAccessResource.

Any related issues, documentation, discussions?

Closes #8353.

Same defect as #6445, fixed in #6446 for ComputingUnitAccessResource only. That fix's rationale assumed the dataset/model/project resources already behaved correctly — true of their grant paths, but not their revoke paths.

How was this PR tested?

Added "reject a revoke for an email with no account" to DatasetAccessResourceSpec and ModelAccessResourceSpec.

sbt "FileService/testOnly *DatasetAccessResourceSpec *ModelAccessResourceSpec"

[info] Tests: succeeded 71, failed 0, canceled 0, ignored 0, pending 0
[info] All tests passed.

Originally found on a local bin/local-dev.sh stack, where DELETE /api/access/dataset/revoke/2/nobody@example.com returned HTTP 500 with:

java.lang.NullPointerException: Cannot invoke "...pojos.User.getUid()" because the return value of "...daos.UserDao.fetchOneByEmail(String)" is null
    at org.apache.texera.service.resource.ResourceAccess$.revoke(ResourceAccess.scala:288)
    at org.apache.texera.service.resource.DatasetAccessResource.$anonfun$revokeAccess$1(DatasetAccessResource.scala:138)

Was this PR authored or co-authored using generative AI tooling?

Generated-by: Claude Code

[github-actions]

Automated Reviewer Suggestions

Based on the git blame history of the changed files, we recommend the following reviewers:

• Contributors with relevant context: @tanishqgandhi1908
  You can notify them by mentioning @tanishqgandhi1908 in a comment.

[github-actions]

Backport auto-label report

This fix: PR was checked against each actively-supported release branch. release/* labels drive the post-merge backport, so add or remove one to change where this fix lands.

Release branch	Analysis
✅ release/v1.3	Change detected on this branch — label added; this fix is queued to backport here. Requested review from @mengw15.
✅ release/v1.2	Change detected on this branch — label added; this fix is queued to backport here. Requested review from @xuang7.

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[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.04%. Comparing base (cd4fd5a) to head (ffc8fac).

Additional details and impacted files

@@            Coverage Diff            @@
##               main    #8384   +/-   ##
=========================================
  Coverage     94.03%   94.04%           
- Complexity     4771     4785   +14     
=========================================
  Files          1196     1196           
  Lines         48757    48778   +21     
  Branches       5916     5918    +2     
=========================================
+ Hits          45850    45871   +21     
  Misses         1458     1458           
  Partials       1449     1449           

Flag	Coverage Δ		*Carryforward flag
access-control-service	81.00% <ø> (ø)
agent-service	99.32% <ø> (ø)		Carriedforward from cd4fd5a
amber	89.89% <ø> (ø)		Carriedforward from cd4fd5a
computing-unit-managing-service	73.67% <ø> (ø)
config-service	89.25% <ø> (+2.12%)	⬆️
file-service	87.92% <100.00%> (+0.01%)	⬆️
frontend	96.81% <ø> (ø)		Carriedforward from cd4fd5a
notebook-migration-service	79.31% <ø> (ø)
pyamber	98.47% <ø> (ø)		Carriedforward from cd4fd5a
workflow-compiling-service	77.19% <ø> (ø)

*This pull request uses carry forward flags. Click here to find out more.

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