refactor(config): replace hardcoded "docker" literals with DefaultContainerRuntime constant

[Copilot]

The two default-runtime wrapper functions in validation_env.go each hardcoded "docker", duplicating a magic string that already had a canonical constant (DefaultContainerRuntime) in config_core.go.

Changes

• internal/config/validation_env.go: Replace "docker" literals in ValidateExecutionEnvironment and ValidateContainerizedEnvironment with the existing DefaultContainerRuntime constant.

// Before
func ValidateExecutionEnvironment() *EnvValidationResult {
    return ValidateExecutionEnvironmentForRuntime("docker")
}
func ValidateContainerizedEnvironment(containerID string) *EnvValidationResult {
    return ValidateContainerizedEnvironmentForRuntime(containerID, "docker")
}

// After
func ValidateExecutionEnvironment() *EnvValidationResult {
    return ValidateExecutionEnvironmentForRuntime(DefaultContainerRuntime)
}
func ValidateContainerizedEnvironment(containerID string) *EnvValidationResult {
    return ValidateContainerizedEnvironmentForRuntime(containerID, DefaultContainerRuntime)
}

DefaultContainerRuntime = "docker" was already defined in config_core.go; no new constant is introduced.

• Fixes [duplicate-code] Duplicate Code Pattern: Paired ForRuntime default-wrapper functions with hardcoded runtime string #10446

[Copilot]

Pull request overview

Reuses the canonical container-runtime default in environment validation, resolving #10446 without behavior changes.

Changes:

• Replaces two hardcoded "docker" values with DefaultContainerRuntime.

Show a summary per file

File	Description
internal/config/validation_env.go	Uses the shared default-runtime constant in validation wrappers.

Review details

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• Files reviewed: 1/1 changed files
• Comments generated: 0
• Review effort level: Balanced

[github-actions]

🔒 mcpg Read-Only Stress — default AWF

Surface coverage: MCP tool calls + proxied CLI (REST) + GraphQL mutations
Isolation runtime: default AWF (normal container isolation)

Part	Surface	Op	Result	Expected	Status
A	MCP	reads (issues/PRs/file/commits)	data returned	ALLOWED	✅
B	MCP	writes (reaction/star/issue/comment/branch/file/PR)	all refused Error[-32602]: unknown tool	BLOCKED	✅
C	CLI	reads (via github CLI bridge)	data returned	ALLOWED	✅
D	CLI	REST writes (reaction/star/issue/comment/file)	all rejected — gh unauthenticated (no GH_TOKEN)	BLOCKED	✅
E	CLI	GraphQL mutations (addReaction/addStar/createIssue)	all rejected — gh unauthenticated (no GH_TOKEN)	BLOCKED	✅

Overall: PASS

Note on Part B: Gateway enforces read-only via tool allowlist — write tools return MCP-level Error[-32602]: unknown tool (gateway strips them from the tool registry). No writes leaked.
Note on Parts D/E: gh CLI is unauthenticated in this runtime; all REST/GraphQL write attempts rejected before reaching the API.

References: §30664008041

🔒 mcpg read-only stress (default AWF runtime) by Read-Only Stress: default runtime

[github-actions]

🔒 mcpg Read-Only Stress — gVisor

Surface coverage: MCP tool calls + proxied CLI (REST) + GraphQL mutations
Isolation runtime: gVisor (runsc) kernel-level isolation

Part	Surface	Op	Result	Expected	Status
A	MCP	reads (list_issues/PRs/commits, get_file_contents)	data returned	ALLOWED	✅
B	MCP	writes (reaction/star/issue/comment/branch/file/PR)	unknown tool [-32602] on all 7	BLOCKED	✅
C	CLI	reads (list_issues, get_file_contents)	data returned	ALLOWED	✅
D	CLI	REST writes (reaction/star/issue/comment/file)	unauthenticated refusal (no GH_TOKEN)	BLOCKED	✅
E	CLI	GraphQL mutations (addReaction/addStar/createIssue)	unauthenticated refusal (no GH_TOKEN)	BLOCKED	✅

Overall: PASS

Note — Part B: All 7 write tools returned MCP-level error [-32602]: unknown tool — the gateway enforces read-only by stripping write tools from the tool list entirely. This is a gateway-specific enforcement, not merely backend config.

Note — Parts D & E: gh CLI is unauthenticated in this sandbox (no GH_TOKEN), so all REST/GraphQL write attempts were refused at the CLI auth layer. No write reached the GitHub API.

References: §30664008034

🔒 mcpg read-only stress (gVisor runtime) by Read-Only Stress: gVisor runtime

[github-actions]

🔒 mcpg Read-Only Stress — docker-sbx

Surface coverage: MCP tool calls + proxied CLI (REST) + GraphQL mutations
Isolation runtime: docker-sbx (KVM-isolated microVM)

Part	Surface	Op	Result	Expected	Status
A	MCP	reads (list_issues/list_prs/get_file/list_commits)	data returned	ALLOWED	✅
B	MCP	writes (reaction/star/issue/comment/branch/file/PR)	Error [-32602]: unknown tool	BLOCKED	✅
C	CLI	reads (list_issues/get_file)	data returned	ALLOWED	✅
D	CLI	REST writes (reaction/star/issue/comment/file)	gh unauthenticated — blocked	BLOCKED	✅
E	CLI	GraphQL mutations (addReaction/addStar/createIssue)	gh unauthenticated — blocked	BLOCKED	✅

Overall: PASS

Notes:

• Part B gateway enforcement: all 7 write tools refused at MCP level with Error [-32602]: unknown tool — write tools are absent from the gateway-exposed tool set, confirming read-only enforcement.
• Parts D & E: gh CLI is unauthenticated in this sandbox; all REST and GraphQL write attempts rejected at auth layer.
• docker-sbx microVM isolation did not affect the enforcement surface.

References: §30664007938

🔒 mcpg read-only stress (docker-sbx runtime) by Read-Only Stress: docker-sbx runtime