fix: truncate default harness name for long project names

[jariy17]

Summary

• agentcore project create --name <name> (no --template) defaulted the harness name to the project name. CFN builds the physical HarnessName as ${projectName}_${harnessName}, capped at 40 chars, so any project name > 19 chars produced a name that failed synth with no recovery other than hand-editing agentcore.json and app/<name>/harness.json.
• When the doubled form would exceed the 40-char CFN cap, derive the harness name as <truncated-projectName>_<sha256[:5]> so ${projectName}_${harnessName} stays ≤ 40 chars and distinct project names never collide. Short project names keep the historical harness.name == projectName behavior.

Repro (before this change)

agentcore project create --name HealthCareProfessional
cd HealthCareProfessional
agentcore project deploy
# ✕ Synthesizing CloudFormation templates
#   AgentCore CDK synthesis failed: Harness name
#   "HealthCareProfessional_HealthCareProfessional" is 45 characters;
#   the maximum is 40 (CloudFormation HarnessName limit).

After

projectName (len)	harness.name written to harness.json	CFN physical (len)
shortproj (9)	shortproj (unchanged)	shortproj_shortproj (19)
HealthCareProfessional (22)	HealthCareP_59ceb (17)	HealthCareProfessional_HealthCareP_59ceb (40)

Existing short-name projects: byte-identical output, no behavior change.

Test plan

• bun run typecheck
• bun test src/handlers/project/create/ (24/24 pass)
• Scaffold HealthCareProfessional locally; confirm harness.json receives HealthCareP_59ceb and derived CFN name is exactly 40 chars
• Scaffold shortproj locally; confirm harness name is unchanged
• Full agentcore project deploy against real AWS (skipped — no fixture account handy; reviewers may want to spot-check)

Notes

• Not addressed here: project add harness (separate handler; users passing a name explicitly are still expected to pick something short) and projects with name > ~34 chars, where no harness name can fit and a create-time validation error would be the right guardrail. Happy to add in a follow-up if reviewers want.
• The underlying constraint lives in @aws/agentcore-l3-cdk-constructs — fixing it there (turn the synth-time throw into a deterministic truncation + Annotations.addWarning) would eliminate the trap at the root and cover every scaffolder, not just project create. This CLI fix stops the bleed today.

[agentcore-devx-automation]

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

[agentcore-devx-automation]

AgentCore Harness Review

Verdict: Looks good

Nice small fix. Math checks out for the reachable input space: ProjectNameSchema caps project names at 23 chars (^[A-Za-z][A-Za-z0-9]{0,22}$), and for any projectName in [1, 23]:

• Length ≤ 19: returned as-is, combined project_project ≤ 39 chars.
• Length 20–23: budget = 40 - len - 1 ∈ [16, 19], prefixLen = budget - 6 ∈ [10, 13], result is ${prefix}_${5-hex-hash} = budget chars, combined = exactly len + 1 + budget = 40. ✓

Result always starts with a letter (inherited from projectName), so it passes HarnessNameSchema's ^[a-zA-Z]... regex.

A couple of minor observations that don't block:

• The prefixLen <= 0 fallback in defaultHarnessNameFor (src/handlers/project/create/index.ts:184) is currently unreachable given ProjectNameSchema.max(23), but if it ever were reached it would return a bare 5-char hex hash, which can begin with a digit and would fail HarnessNameSchema's leading-letter regex. Consider prefixing the hash with a letter (e.g. h${hash}) or asserting/erroring, to make the helper self-consistent independent of upstream validation.
• No unit tests were added for defaultHarnessNameFor. Given it's a pure function with tight boundary conditions around the 40-char CFN cap, a quick test covering the 19/20-char boundary and the max-23 case would be worthwhile — this is exactly the kind of arithmetic that regresses silently if either limit changes.

[agentcore-devx-automation]

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

[agentcore-devx-automation]

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

[codecov-commenter]

Codecov Report

❌ Patch coverage is 71.42857% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 96.97%. Comparing base (9be9780) to head (b83a66d).
⚠️ Report is 3 commits behind head on refactor.

Files with missing lines	Patch %	Lines
src/handlers/project/create/index.ts	71.42%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##           refactor    #2233      +/-   ##
============================================
- Coverage     96.97%   96.97%   -0.01%     
============================================
  Files           559      559              
  Lines         38581    38587       +6     
============================================
+ Hits          37414    37418       +4     
- Misses         1167     1169       +2     

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