Milestone 3.5.C.5 — Context FormatterCopy Anchor Link

Status: Completed Goal: Track C — Context Assembly Engine
Phase: 3.5 — Extraction & Context Assembly
Estimated effort: 2 days
Track: Track C — Context Assembly Engine
Depends on: 3.5.C.4 (packer v2)
ADR: ADR-0070

Why This Milestone ExistsCopy Anchor Link

Memories are untrusted input and must be wrapped as data with a per-assembly nonce (SECURITY.md §7.3). Conversation history is trusted and must stay as native role messages. Planning docs disagreed on history position; this milestone locks order in code + ADR and corrects ARCHITECTURE.md’s stale “history last” line.

Non-GoalsCopy Anchor Link

• Full AssembleContext orchestrator (budget → retrieve → score → pack → format) — 3.5.C.6
• gRPC / proto changes
• Amending ADR-0038 (gRPC contract) or ADR-0042 (self-hosted LLM adapter)

File layout (as shipped)Copy Anchor Link

services/context/app/formatter.py   # ContextFormatter, FormattedContext, CATEGORY_ORDER
services/context/app/config.py      # IBEX_CONTEXT_FORMATTER_NONCE_BYTES
services/context/tests/test_formatter.py

Settings / env:

• IBEX_CONTEXT_FORMATTER_NONCE_BYTES (default 16) — secrets.token_urlsafe nbytes

Final Locked OrderingCopy Anchor Link

1. Directive (always first — sets behavior before any content)
2. Conversation history (native role: content lines — not XML-wrapped)
3. Memories by category (procedural → factual → preference → behavioral → episodic)
4. Tool schemas (if applicable)

Rationale for History in position 2: “lost in the middle” — history stays near the start where attention is reliable.

Memory wrap:

<ibex_memory nonce="{nonce}" id="{memory_id}" category="{category}">
{content}
</ibex_memory>

Success signalsCopy Anchor Link

• CATEGORY_ORDER = procedural → factual → preference → behavioral → episodic
• History at position 2 as native role: content (not XML-wrapped)
• ADR-0070 accepted (new ADR; not ADR-0042)
• Golden-output exact-match fixture (directive + 2 history turns + 3 memories)
• Nonce uniqueness + spoofed-tag neutralization tests
• ARCHITECTURE.md format/budget order aligned with locked ordering