Contract — R93 B6 stake_discount_bps Rename

Round: R93 debug-sweep · XS scope Audit: docs/audits/r93-b6-reputation-field-rename-audit.md β task: 2e8978e9-e83d-4c3a-a20a-bf66cacc9251

§1. Invariants

ID	Invariant
I-1	reputation_check_gates MCP output uses field name effective_stake_bps (not stake_discount_bps).
I-2	The underlying stake_discount(...) function name at src/domains/reputation/limits.ts:172 is unchanged.
I-3	The arithmetic is unchanged. For an unknown node (score=0, stake=10000), the output value remains 100000.
I-4	src/__tests__/domains/reputation/tools.test.ts references the new field name; tests pass.
I-5	MCP tool description string in registerColibriTool reflects the new field name.
I-6	Build + lint + test gates remain green.

§2. Non-invariants

• N-1. The underlying stake_discount(...) function name is preserved (it describes the formula).
• N-2. Heritage chain docs (docs/contracts/p2-5-1-tools-contract.md, docs/audits/p2-5-1-tools-audit.md) — field-name references updated to match the new wire shape, but the historical sub-task numbering stays.
• N-3. CLAUDE.md / README / quick-start changelog entries — not modified in this slice.

§3. Acceptance criteria

• AC-1. git grep stake_discount_bps returns 0 hits in the worktree HEAD.
• AC-2. git grep effective_stake_bps returns the same locations the old name occupied (5 files).
• AC-3. npm run build && npm run lint && npm test exit 0.

Proceeding to packet.