feat: add production-side compile-time interface assertions for engine and condition types

[Copilot]

The repo had zero production-side var _ Interface = (*Concrete)(nil) guards — all 7 CodingAgentEngine implementors and all 10 ConditionNode node types were entirely unguarded, meaning a broken contract surfaces at a distant call site rather than at the declaration.

Changes

• 7 CodingAgentEngine assertions — one guard added directly after each struct definition:

  • CopilotEngine, ClaudeEngine, CodexEngine, GeminiEngine, AntigravityEngine, PiEngine, BehaviorDefinedEngine

• 10 ConditionNode assertions — grouped block added in expression_nodes.go immediately after the interface declaration:

  • ExpressionNode, AndNode, OrNode, NotNode, DisjunctionNode, FunctionCallNode, PropertyAccessNode, StringLiteralNode, BooleanLiteralNode, ComparisonNode

// expression_nodes.go
var (
    _ ConditionNode = (*ExpressionNode)(nil)
    _ ConditionNode = (*AndNode)(nil)
    _ ConditionNode = (*OrNode)(nil)
    // ... 7 more
)

// behavior_defined_engine.go
var _ CodingAgentEngine = (*BehaviorDefinedEngine)(nil)

Zero runtime overhead. Engine refactors now fail at the declaration site.

[github-actions]

✅ PR Code Quality Reviewer completed the code quality review.

[github-actions]

✅ Design Decision Gate 🏗️ completed the design decision gate check.

No ADR enforcement needed: PR does not have the 'implementation' label and has ≤100 new lines of code in business logic directories (28 additions detected).

[github-actions]

✅ Test Quality Sentinel completed test quality analysis.

No test files were added or modified in this PR. Test Quality Sentinel skipped.

[Copilot]

Pull request overview

This PR adds production-side compile-time interface assertions to ensure all CodingAgentEngine implementations and all ConditionNode expression node types continue to satisfy their respective interfaces, causing contract breaks to fail at the type declaration site instead of at downstream call sites.

Changes:

• Added var _ CodingAgentEngine = (*<Engine>)(nil) assertions for each of the 7 engine structs.
• Added a grouped var (...) block asserting all 10 ConditionNode implementation types satisfy ConditionNode.

Show a summary per file

File	Description
pkg/workflow/pi_engine.go	Adds compile-time assertion that *PiEngine implements CodingAgentEngine.
pkg/workflow/gemini_engine.go	Adds compile-time assertion that *GeminiEngine implements CodingAgentEngine.
pkg/workflow/expression_nodes.go	Adds grouped compile-time assertions that all ConditionNode node types implement ConditionNode.
pkg/workflow/copilot_engine.go	Adds compile-time assertion that *CopilotEngine implements CodingAgentEngine.
pkg/workflow/codex_engine.go	Adds compile-time assertion that *CodexEngine implements CodingAgentEngine.
pkg/workflow/claude_engine.go	Adds compile-time assertion that *ClaudeEngine implements CodingAgentEngine.
pkg/workflow/behavior_defined_engine.go	Adds compile-time assertion that *BehaviorDefinedEngine implements CodingAgentEngine.
pkg/workflow/antigravity_engine.go	Adds compile-time assertion that *AntigravityEngine implements CodingAgentEngine.

Review details

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• Files reviewed: 8/8 changed files
• Comments generated: 0
• Review effort level: Low

[github-actions]

🧠 Matt Pocock Skills Reviewer has completed the skills-based review. ✅

[github-actions]

LGTM. Straightforward compile-time interface assertions placed correctly at declaration sites. No issues found.

🧵 Reviewed using Impeccable skills by Impeccable Skills Reviewer · 11.4 AIC · ⌖ 6.68 AIC · ⊞ 5K

[github-actions]

Skills-Based Review 🧠

Applied /codebase-design — changes are solid.

📋 Key Themes & Highlights

Key Themes

• Correct idiom — var _ Interface = (*Concrete)(nil) is the canonical Go compile-time assertion pattern; all 17 guards are correctly placed immediately after struct definitions.
• Zero runtime cost — no behavioural change, purely a compile-time safety net.
• Grouped vs scattered — ConditionNode assertions are consolidated in a single var (\u2026) block in expression_nodes.go; CodingAgentEngine assertions are one-per-file. This is a minor inconsistency (see inline comment).

Positive Highlights

• ✅ Placement immediately after each struct definition makes the contract visible at the declaration site.
• ✅ Grouped block for ConditionNode types is easy to scan at a glance.
• ✅ PR description is clear and self-contained.

🧠 Reviewed using Matt Pocock's skills by Matt Pocock Skills Reviewer · 18.1 AIC · ⌖ 4.41 AIC · ⊞ 6.7K
_{Comment /matt to run again}

[github-actions]

[/codebase-design] Minor: the CodingAgentEngine assertions are scattered one-per-file while the ConditionNode assertions are consolidated in a single var (...) block. Consider grouping all engine assertions in a dedicated file (e.g. engine_assertions.go) or at minimum alongside the CodingAgentEngine interface declaration, to make the full set of implementors visible at a glance — mirroring the style already used in expression_nodes.go.

@copilot please address this.

[github-actions]

Compile-time interface guards are correctly placed and complete.

Coverage check

CodingAgentEngine (7 types)

All 6 builtins registered in NewEngineRegistry plus BehaviorDefinedEngine (registered dynamically) are guarded. UniversalLLMConsumerEngine is a mixin only, never directly registered — no guard needed there.

ConditionNode (10 types)

Grouped block in expression_nodes.go covers all concrete node types visible in the package.

Placement

Guards are placed immediately after each struct definition, which is the idiomatic Go convention for these assertions. Zero runtime overhead, correct semantics.

🔎 Code quality review by PR Code Quality Reviewer · 50.7 AIC · ⌖ 4.32 AIC · ⊞ 5.6K
_{Comment /review to run again}

[github-actions]

🎉 This pull request is included in a new release.

Release: v0.82.10