fix(agent-core): keep profile-routed subagent model on resume and retry

[elkaix]

Related Issue

No issue — problem described below.

Problem

An agent profile can route its subagents to a different model (a cheap
implementer under an expensive orchestrator, for example). That routing only
held on the initial spawn: resuming or retrying a subagent copied the parent
agent's model alias onto the child, so from the second turn on the subagent
silently ran on the orchestrator's model and the profile's effort setting was
dropped.

What changed

Resume and retry now re-resolve the child's model through the same precedence
as spawn — explicit run option, then profile, then parent — instead of copying
the parent's model. An alias the child's provider cannot resolve falls back to
the parent's model rather than failing at generate time. Added a regression
test covering resume with a profile-routed model and effort.

Checklist

• I have read the CONTRIBUTING document.
• I have linked a related issue, or explained the problem above.
• I have added tests that prove my feature works.
• Ran gen-changesets skill, or this PR needs no changeset.
• Ran gen-docs skill, or this PR needs no doc update. (internal behavior, no CLI docs surface)

Summary by CodeRabbit

• Bug Fixes
  • Subagents now retain their assigned model and effort settings when resumed or retried.
  • Invalid or unavailable model aliases gracefully fall back to the parent agent’s model.
  • Profile configuration issues no longer prevent subagent resume or retry operations.

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Review details

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

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Run ID: e6f953f3-442d-42a4-8704-5a96a4ec942f

📥 Commits

Reviewing files that changed from the base of the PR and between ba48a91 and f6a2d58.

📒 Files selected for processing (1)

• packages/agent-core/test/session/subagent-host.test.ts

📝 Walkthrough

Walkthrough

Subagent initialization, resume, and retry now use centralized configuration. Profile-selected model aliases and effort levels are preserved when aliases resolve, with fallback to the parent model when they do not.

Changes

Subagent model preservation

Layer / File(s)	Summary
Model alias resolution packages/agent-core/src/agent/config/index.ts	ConfigState exposes canResolveModel. Provider resolution now accepts an explicit model alias while preserving fallback behavior.
Centralized child configuration packages/agent-core/src/session/subagent-host.ts, packages/agent-core/test/session/subagent-host.test.ts, .changeset/keep-subagent-routed-model.md	Initial setup, resume, and retry use shared configuration. Explicit options take priority, followed by profile settings and parent defaults. Tests verify preservation of the profile-routed model and effort.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Sequence Diagram(s)

sequenceDiagram
  participant SubagentHost
  participant ProfileResolver
  participant ConfigState
  participant ChildAgent
  SubagentHost->>ProfileResolver: Resolve profile settings
  ProfileResolver-->>SubagentHost: Return model and effort
  SubagentHost->>ConfigState: Validate model alias
  ConfigState-->>SubagentHost: Return resolution status
  SubagentHost->>ChildAgent: Apply model, effort, thinking level, and fast mode

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🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title uses the fix prefix, stays within 72 characters, uses imperative mood, and clearly describes the subagent model-routing correction.
Description check	✅ Passed	The description includes all required sections, explains the problem and solution, and confirms tests, changesets, documentation, and contribution checks.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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npx https://pkg.pr.new/@pythoughts/pythinker-code@f6a2d58

commit: f6a2d58

[coderabbitai]

🧹 Nitpick comments (1)

packages/agent-core/test/session/subagent-host.test.ts (1)

1375-1425: 📐 Maintainability & Code Quality | 🔵 Trivial | ⚡ Quick win

Cover profile-routed configuration in retry.

The existing host.retry test covers rate-limit recovery but not profile-selected configuration. Add a Vitest case that retries a profile-routed child and asserts modelAlias and thinkingLevel retain the profile values.

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@packages/agent-core/test/session/subagent-host.test.ts` around lines 1375 -
1425, Add a Vitest case for SessionSubagentHost.retry that configures a child
with a routed ResolvedAgentProfile, triggers a retry, and verifies the retry
preserves the profile’s modelAlias and thinkingLevel rather than the parent
configuration. Reuse the existing profile-routing setup and assertions from the
resume test while exercising retry-specific flow.

Source: Coding guidelines

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Nitpick comments:
In `@packages/agent-core/test/session/subagent-host.test.ts`:
- Around line 1375-1425: Add a Vitest case for SessionSubagentHost.retry that
configures a child with a routed ResolvedAgentProfile, triggers a retry, and
verifies the retry preserves the profile’s modelAlias and thinkingLevel rather
than the parent configuration. Reuse the existing profile-routing setup and
assertions from the resume test while exercising retry-specific flow.

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

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Run ID: c2af45df-3e70-4496-b19e-324a06fd32f0

📥 Commits

Reviewing files that changed from the base of the PR and between 251fb87 and ba48a91.

📒 Files selected for processing (4)

• .changeset/keep-subagent-routed-model.md
• packages/agent-core/src/agent/config/index.ts
• packages/agent-core/src/session/subagent-host.ts
• packages/agent-core/test/session/subagent-host.test.ts