refactor: replace raw engine strings with typed constants.*Engine

[Copilot]

Switch statements and inline comparisons over engineID in compiler_yaml_lookups.go, firewall.go, and strict_mode_permissions_validation.go used raw string literals ("copilot", "claude", "codex", etc.) despite typed constants already existing in pkg/constants. Typos silently misroute behavior with no compiler or IDE feedback.

Changes

• compiler_yaml_lookups.go — Replace raw string cases in all 4 switches (getVersionForSetup, getInstallationVersion, getDefaultAgentModel, getDefaultModelOverrideVar)
• firewall.go — Replace raw string comparisons in enableFirewallByDefaultForCopilot and enableFirewallByDefaultForClaude
• strict_mode_permissions_validation.go — Replace raw string comparison in validateStrictFirewall; add constants import

// Before
switch engineID {
case "copilot":
    return string(constants.DefaultCopilotVersion)
case "claude":
    return string(constants.DefaultClaudeCodeVersion)
}

if engineID != "copilot" && engineID != "codex" { ... }

// After
switch engineID {
case string(constants.CopilotEngine):
    return string(constants.DefaultCopilotVersion)
case string(constants.ClaudeEngine):
    return string(constants.DefaultClaudeCodeVersion)
}

if engineID != string(constants.CopilotEngine) && engineID != string(constants.CodexEngine) { ... }

engineID remains string throughout — no signature changes. The string(constants.*Engine) cast is the lowest-risk approach and requires no refactoring outside these three files.

[Copilot]

Pull request overview

Replaces raw engine string literals ("copilot", "claude", "codex", "opencode", "crush", "pi", "gemini") with the typed constants.*Engine values (cast to string) in three workflow files, eliminating typo risk and aligning with constants already defined in pkg/constants/engine_constants.go.

Changes:

• Switch cases in compiler_yaml_lookups.go (4 functions) updated to use string(constants.*Engine).
• Engine comparisons in firewall.go (enableFirewallByDefaultForCopilot, enableFirewallByDefaultForClaude) updated similarly.
• strict_mode_permissions_validation.go updated, adding the constants import.

Show a summary per file

File	Description
pkg/workflow/compiler_yaml_lookups.go	Replaces raw strings with typed engine constants in version/model lookup switches.
pkg/workflow/firewall.go	Uses typed constants for engine comparisons in default-firewall helpers.
pkg/workflow/strict_mode_permissions_validation.go	Uses typed constants for engine check; adds constants import.
.github/workflows/outcome-collector.lock.yml	Regenerated lock file with version/image bumps; unrelated to refactor purpose.

Copilot's findings

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• Files reviewed: 4/4 changed files
• Comments generated: 0