gate prepare resolves operator-supplied artifact paths without doubling

[clkao]

Gate reviews now accept operator-supplied paths without doubled state roots, keeping approval work moving under the no-retry rule.

What changed

• Resolve artifact and reference paths against explicit launch context.
• Preserve omitted-context wrong-root refusal.
• Fail ambiguous and unsafe sources before mutation.
• Align operator and First Officer documentation.

Evidence

• Full and race suites: 22/22 packages passed each.
• Layer surface: +183 net LOC across 6 files versus +151 estimated.
• Approved tolerance: +110 to +215 net LOC and at most 7 files.

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9n