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Agentic-Bridle/docs/adr/0005-get-rules-tool-with-session-gating.md
wtclaude 06917d43e2 docs: add phased implementation plan and architecture decision records 
Turns the design doc into an ordered, dependency-correct build plan (phases
0-9) with an exit criterion per phase, and records the twelve architectural
decisions it rests on as ADRs.

Decisions: single Rust binary with routed compose services; Streamable HTTP
only; per-agent bearer tokens with clientInfo as a display hint only; SQLite;
get_rules delivered via session gating; full-document rule delivery; project_id
from day one; enforcement tier scoped to Bridle-mediated actions; stable tool
list on upstream failure; OpenAI-compatible embeddings with model/dim guarding;
pattern RAG gated behind a spike; CLAUDE.md + AGENTS.md as v1 renderer targets.

Deviates from the design doc's original 1-8 ordering by moving the audit log
and multi-project schema into phase 1, building the admin API incrementally
rather than all at the Web Panel phase, downgrading vendor guardrail sourcing
to manual-first, and gating the pattern-example RAG behind a validation spike.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019RZerbsHGF9Ka3bKhCjJ9m
2026-08-08 14:33:27 -05:00

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ADR-0005: Rules delivered via get_rules, enforced by session gating

Status: Accepted (2026-08-08)

Context

Bridle's premise is that the canonical ruleset governs every agent session. But an MCP server can only offer a get_rules tool — it cannot make a model call it. Meanwhile Claude Code auto-loads CLAUDE.md from disk and Codex auto-loads AGENTS.md from disk, unprompted, every session. A tool the model may skip is strictly weaker than a file the harness injects.

Three delivery mechanisms were considered:

  1. A local sync client (bridle sync or a session-start hook) writing rendered files to disk — reliable across agents today, but adds a client-side component the design doc does not have.
  2. The instructions field of the MCP initialize result — no client install, but whether a given client injects it into the system prompt varies and would need per-agent empirical testing.
  3. The get_rules tool alone — matches the design doc, but leaves delivery best-effort.

Decision

Deliver rules through the get_rules(project_id, agent_type) tool, and make it reliable by gating the session: any other tool call before get_rules has succeeded returns a structured error naming the required call. Per-session state tracks whether rules have been fetched.

Consequences

  • Delivery becomes effectively guaranteed using only the in-band MCP mechanism — no client-side component to install or maintain per agent.
  • Costs one extra round-trip at the start of each session.
  • The error message is part of the product surface and must be unambiguous enough that an agent recovers on the first try.
  • Populating the initialize instructions field remains available later as belt-and-braces. It reuses the same renderer, requires no client install, and does not change this architecture.
  • Session state now matters: the gate flag must be scoped to the MCP session, and session loss means re-fetching.