fix(migrate): make the plan and next steps easier to read

[notgitika]

Description

Addresses the readability feedback on agentcore migrate from the bug bash notes:

• Spacing. There's now a blank line between the progress lines (✓ Planning the refactor of …) and Migration plan: …. With --yes, there's also one before apply's progress.
• Test-library note. The AGENTCORE_MIGRATE_CDK_LIBRARY note comes after Full plan: … and is one line. The install command only appears after migrating, in the next steps, which is when it's needed. This only shows when the test override is set.
• Install from the project root. The install command is now npm install --prefix agentcore/cdk <lib> --no-save instead of cd agentcore/cdk && …, so agentcore deploy runs right after it without changing directory. It also works the same in shells where cd … && doesn't.
• Plan file stack section:
  • It's flatter, with one First v1 deploy: … line and then one row per change (creates, deletes, replaces, updates).
  • Expected in-place updates no longer carry a warning label. That label made it look like there were two warning sections.
  • The separate Replacements: verdict is folded into the First v1 deploy line, which now also counts resources that must be kept.
  • A note under the refactor table explains that the new logical IDs come from the v1 CDK app's construct paths, and that only the IDs change.

Before:

  Then the first v1 deploy:
    updates in place
      warning AWS::BedrockAgentCore::Runtime ApplicationRuntimeAgentRuntime93CA6260: the v1 deploy updates it in place: EnvironmentVariables, … change
    creates, deletes, and replaces nothing else
  Replacements: 0 replacements; no resource that must be kept is replaced or deleted

After:

  First v1 deploy: replaces nothing; updates 1 resource in place
    updates   AWS::BedrockAgentCore::Runtime ApplicationRuntimeAgentRuntime93CA6260: EnvironmentVariables, … change

Related Issue

No public issue; this addresses bug bash feedback on #2584.

Documentation PR

Not applicable (CLI output only).

Type of Change

• Bug fix
• New feature
• Breaking change
• Documentation update
• Other (please describe):

Testing

• I ran bun test
• I ran the relevant end-to-end tests with bun run test:e2e, or explained why they are not applicable. Instead of e2e, I ran it live: I deployed a new v0 project (runtime, memory and gateway) with CLI 0.31.1, previewed and migrated it with this build, then ran the printed npm install --prefix … and agentcore deploy from the project root. The deploy succeeded.
• I ran bun run typecheck
• I ran bun run lint:check
• I ran bun run format:check
• I ran bun run build
• If I modified src/assets/, I updated affected snapshots with bun test <test-file> --update-snapshots and committed them

Checklist

• I have read the CONTRIBUTING document
• I have added any necessary tests that prove my fix is effective or my feature works
• I have updated the documentation accordingly
• I have added an appropriate example to the documentation to outline the feature, or no new docs are needed
• My changes generate no new warnings
• Any dependent changes have been merged and published

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[agentcore-devx-automation]

Claude Security Review: no high-confidence findings. (run)

[agentcore-devx-automation]

AgentCore Harness Review

Verdict: Looks good

This is a focused presentation/wording cleanup for agentcore migrate with matching test updates. The logic changes are small and sensible:

• deployImpact now computes mustKeep and renders the actual blocker count. Previously the branch always said (none that must be kept) even when there were blockers in replaced/removed — this is a real bug fix.
• The rows() helper unifies the per-change rendering; action is padded to width 8, which fits all four verbs (creates/deletes/replaces/updates).
• overrideInstallCommand switches from cd agentcore/cdk && npm install … to npm install --prefix agentcore/cdk … --no-save, which keeps the user in the project root so the follow-up agentcore deploy just works. --prefix has been supported by npm for a long time.
• The redundant the v1 deploy updates it in place: prefix is dropped from the update reason now that the row's action column already says updates.

Nothing jumped out as needing changes before merge.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.59%. Comparing base (c480abb) to head (4235806).

Additional details and impacted files

@@            Coverage Diff            @@
##           refactor    #2612   +/-   ##
=========================================
  Coverage     96.58%   96.59%           
=========================================
  Files           700      700           
  Lines         57638    57631    -7     
=========================================
- Hits          55672    55666    -6     
+ Misses         1966     1965    -1     

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