feat(e2b): support naming cloned sandbox via metadata extensions

[AiRanthem]

Summary

• Adds two new metadata keys for POST /sandboxes on the clone path:
  • e2b.agents.kruise.io/sandbox-name — sets ObjectMeta.Name (mutually exclusive with the next).
  • e2b.agents.kruise.io/sandbox-generate-name — sets ObjectMeta.GenerateName prefix.
• Default behavior is unchanged when neither key is provided (GenerateName: <checkpointID>-).
• Validates inputs as DNS-1123 label (apivalidation.NameIsDNSLabel); the canonical K8s validator with prefix=true masks the trailing - for GenerateName prefixes. Both keys are stripped from Metadata so they don't leak onto sandbox annotations.
• AlreadyExists collision (only reachable when sandbox-name is set) maps to 409 Conflict via the manager's typed ErrorConflict.
• Naming is a first-class field on infra.CloneSandboxOptions; newSandboxFromTemplate uses an explicit switch so the Name/GenerateName precedence is visible at the call site rather than relying on K8s semantics.

Public-contract note (beyond the design spec)

The claim path actively rejects these keys with 400 Bad Request (sandbox-name and sandbox-generate-name are only supported for clone). Caller-controlled naming on the claim path is owned by SandboxSet and is out of scope; failing fast is preferable to silently dropping the request.

Design

docs/superpowers/specs/2026-05-12-clone-sandbox-name-design.md (in the design branch; not included in this PR).

Test plan

• go build ./...
• go vet ./pkg/servers/e2b/... ./pkg/sandbox-manager/...
• go test ./pkg/servers/e2b/... ./pkg/sandbox-manager/...
• parseExtensionSandboxNaming table covers mutual exclusion, empty values, dot rejection, trailing-dash prefix, and key-stripping.
• ValidateAndInitCloneOptions rejects both Name and GenerateName set together.
• newSandboxFromTemplate honors Name, GenerateName, and falls back to <checkpointID>-.
• TestCreateSandboxWithClone_Naming end-to-end: Extensions.Name / Extensions.GenerateName flow through to the resulting Sandbox ObjectMeta.
• TestSandboxManager_CloneSandbox "explicit name collision returns conflict" maps to ErrorConflict.
• TestMapCloneSandboxError confirms only manager-wrapped conflict maps to 409 (raw apierrors.AlreadyExists is not specially mapped — manager is expected to wrap).
• TestCreateSandboxWithClaim_NamingExtensionRejected confirms claim path returns 400.

[kruise-bot]

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[codecov]

Codecov Report

❌ Patch coverage is 92.72727% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 76.01%. Comparing base (5d3212b) to head (a0f1110).
⚠️ Report is 3 commits behind head on master.

Files with missing lines	Patch %	Lines
pkg/servers/e2b/models/extensions.go	86.20%	2 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #385      +/-   ##
==========================================
+ Coverage   75.90%   76.01%   +0.10%     
==========================================
  Files         145      145              
  Lines       10626    10673      +47     
==========================================
+ Hits         8066     8113      +47     
  Misses       2212     2212              
  Partials      348      348              

Flag	Coverage Δ
unittests	76.01% <92.72%> (+0.10%)	⬆️

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[kruise-bot]

@AiRanthem: PR needs rebase.

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