fix(deepagents): replace same-name middleware in createDeepAgent

[Hunter Lovell (hntrl)]

Summary

createDeepAgent now merges user-provided middleware into the assembled middleware stack by .name, replacing matching entries in place instead of appending duplicates. This gives users a direct path to override built-in middleware configuration (such as summarization) without introducing duplicate triggers. The same replacement behavior now applies to declarative subagent middleware stacks.

Changes

libs/deepagents/src/agent.ts

• Reused shared middleware merge semantics when composing the root middleware stack, so matching middleware names replace existing entries at their current position.
• Applied the same merge-by-name behavior to declarative subagent middleware assembly before cache middleware is appended.
• Preserved existing stack ordering guarantees while preventing duplicate named middleware.

libs/deepagents/src/profiles/harness/merge.ts

• Exported mergeMiddleware so the same merge-by-name logic can be reused by createDeepAgent.

libs/deepagents/src/agent.test.ts

• Added coverage for root middleware replacement by name and declarative subagent middleware replacement by name.
• Asserted both de-duplication (SummarizationMiddleware appears once) and ordering behavior.

.changeset/hunter-middleware-replace-by-name.md

• Added a patch changeset for deepagents describing the middleware replacement behavior.

[changeset-bot]

🦋 Changeset detected

Latest commit: 1decaab

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 3 packages

Name	Type
deepagents	Patch
deepagents-acp	Patch
@deepagents/evals	Patch

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