api: cap Get result capacity to lower retained heap

[snissn]

Summary

• cap Tree.Get return slice capacity to len(out) so API callers don't retain append-growth headroom
• apply the same cap behavior in Snapshot.Get for consistency
• strengthen TestGet_SafeCopy to assert cap(result)==len(result) for Get

Why

Get is an ownership boundary. Returning extra capacity can accidentally pin oversized backing arrays and inflate retained heap/RSS under heavy read/reuse patterns.

Validation

• go test ./TreeDB ./TreeDB/caching ./TreeDB/tree -count=1
• go vet ./TreeDB ./TreeDB/caching ./TreeDB/tree

[Copilot]

Pull request overview

This PR tightens TreeDB’s Get ownership boundary by ensuring returned []byte slices are capacity-cipped to their length, preventing callers from accidentally retaining append-growth headroom and inflating retained heap.

Changes:

• Cap tree.Tree.Get return slice capacity to len(out) via full-slice expression.
• Apply the same capacity capping behavior to cached caching.Snapshot.Get.
• Strengthen TestGet_SafeCopy to assert cap(result) == len(result) for Get.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
TreeDB/tree/tree.go	Caps Tree.Get return capacity to prevent retaining excess backing array capacity.
TreeDB/caching/snapshot.go	Caps Snapshot.Get return capacity for consistent safe-copy semantics in cached snapshots.
TreeDB/api_alloc_test.go	Adds assertions that Get returns a slice with cap == len.

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[Copilot]

Pull request overview

This PR aims to prevent Get APIs from returning []byte values with extra capacity, so callers don’t accidentally retain or reuse append headroom across an ownership boundary.

Changes:

• Cap the returned slice capacity in tree.Tree.Get to len(out) via a full-slice expression.
• Apply the same capacity-capping behavior in caching.Snapshot.Get.
• Strengthen TestGet_SafeCopy to assert cap(result) == len(result) for DB.Get.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
TreeDB/tree/tree.go	Caps Tree.Get return slice capacity to length and documents rationale.
TreeDB/caching/snapshot.go	Wraps Snapshot.Get to cap capacity after calling GetAppend.
TreeDB/api_alloc_test.go	Adds assertions that Get returns a slice with cap==len.

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[Copilot]

Pull request overview

Caps Get return slice capacity to its length so callers don’t retain append-growth headroom and unintentionally pin large backing arrays, reducing retained heap/RSS.

Changes:

• Cap Tree.Get’s returned []byte capacity to len(out) using full slice expressions.
• Apply the same capacity-capping behavior to Snapshot.Get.
• Strengthen TestGet_SafeCopy to assert cap(result) == len(result) for Get.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
TreeDB/tree/tree.go	Caps Tree.Get return slice capacity to length to avoid retaining excess backing array capacity.
TreeDB/caching/snapshot.go	Updates Snapshot.Get to cap returned slice capacity similarly (with explicit error handling).
TreeDB/api_alloc_test.go	Adds assertions ensuring Get results are capacity-capped to length.

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