fix(delegate-task): apply getAgentConfigKey normalization to isPlanAgent

[codeg-dev]

Summary

isPlanFamily was already fixed (in a previous commit) to normalize display names via getAgentConfigKey(), but isPlanAgent still used raw agentName.toLowerCase() without normalization.

This PR applies the same fix to isPlanAgent for consistency and correctness.

Changes

src/tools/delegate-task/constants.ts

• isPlanAgent: normalize agentName through getAgentConfigKey() before comparison (same as isPlanFamily)

src/tools/delegate-task/tools.test.ts

• Fix misleading test title: "returns true for 'planner' (matches via includes('plan'))" → describes the old bug, but assertion was already false. Corrected to "returns false for 'planner' (no longer matches via substring)"
• Add regression test for isPlanAgent with Metis/Momus/Atlas display names (all should return false)
• Add regression test for isPlanFamily with Metis/Momus/Atlas display names (all should return false)

Root Cause (from #3312)

Four agents have "(Plan ...)" or "- Plan ..." in their display names:

Config key	Display name
atlas	"Atlas - Plan Executor"
metis	"Metis - Plan Consultant"
momus	"Momus - Plan Critic"
prometheus	"Prometheus - Plan Builder"

Without getAgentConfigKey() normalization, display names containing "plan" as a substring could produce false-positives, and display names for legitimate plan-family agents (prometheus) would fail to match.

Testing

bun test src/tools/delegate-task/tools.test.ts --filter 'isPlan'
# 129 pass, 0 fail

Fixes #3312

---

Summary by cubic

Normalize agent names in isPlanAgent using getAgentConfigKey to avoid display-name mismatches and keep behavior consistent with isPlanFamily. Fixes #3312.

• Bug Fixes
  • Apply getAgentConfigKey normalization in isPlanAgent before comparing to PLAN_AGENT_NAMES.
  • Correct test title for "planner" (returns false; no substring match).
  • Add regression tests to ensure Metis/Momus/Atlas display names are not treated as plan or plan-family.

^{Written for commit 23d1257. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 2 files

Confidence score: 5/5

• Automated review surfaced no issues in the provided summaries.
• No files require special attention.

_{Auto-approved: Standardizes agent name normalization using getAgentConfigKey to ensure consistency and correct matching of display names, supported by new regression tests.}