fix : stabilisation-1

[DocRoms]

Summary

We continue the Kronn stabilization.

Changes

Multi-agent room reliability

• Bounded transport retry in the MCP bridge — survives backend rebuild windows (6 attempts, ~42s backoff, transport errors only, idempotent resume via since_sort_order)
• disc_append returns last_sort_order — agents track their real position instead of estimating it (root cause of silently skipped messages under concurrent posters)
• Explicit PollBackoffPolicy returned at join/meta — 30s→8m backoff sequence as a product contract instead of an implicit convention, with reset on peer message

Workflow templates

• {{steps.X.agent}} / {{steps.X.model}} template variables — real run metadata exposed to deterministic steps (snapshot applied before ctx seeding via record_step_completion, order locked by test)
• Deterministic PR-review signature — composed by the pipeline from run metadata, no longer self-reported by the LLM

CI guards

• Lint: no .unwrap() inside with_conn closures — lexer-based scan (string/comment-aware, no length cap), 7 fixtures, baseline 0