feat: Tiered history retrieval (hot/cold layer pattern)

Feature Proposal: Tiered History Retrieval

Problem

Agent history.md files grow unbounded. Currently Scribe summarizes at 12KB, but agents read everything — no distinction between recent context and archived knowledge. This wastes context window tokens and slows agent startup.

Proposed Solution

Formalize a two-tier retrieval pattern inspired by ClawMongo's tiered projection model:

Hot layer (history.md): Last ~20 entries. Always read at spawn time. Fresh, actionable context.
Cold layer (history-archive.md): Summarized older entries. Read only when agent explicitly needs historical context.

Implementation

Spawn prompt change: agents read history.md (hot) by default. Only read history-archive.md when the task references past decisions or old patterns.
Scribe summarization: when history.md exceeds threshold, move old entries to archive with summaries (already partially implemented).
Search cold: add a 'search archive' pattern agents can invoke when they need historical context.

Benefits

Reduced context window usage (~60% less tokens for history)
Faster agent startup
No external DB required — pure file-based

Prior Art

Inspired by ClawMongo's tiered retrieval model (https://clawmongo.site) which uses ID-only projections for 10x context reduction. Adapted for Squad's file-based architecture.

feat(skills): add tiered-history skill — hot/cold history split for c…

fix: REPL UX fixes — 10 issues resolved with 52 new tests (github#608)

📋 Assigned to Procedures (Prompt Engineer)

Issue: #595 — feat: Tiered history retrieval (hot/cold layer pattern)

Procedures will pick this up in the next Copilot session.

For Copilot coding agent: If enabled, this issue will be worked automatically.
Otherwise, start a Copilot session and say:
Procedures, work on issue #595

🏗️ Squad Triage — Flight (Lead)

Issue: #595 — feat: Tiered history retrieval (hot/cold layer pattern)
Assigned to: DSKY (TUI Engineer)
Reason: Issue relates to frontend/UI work

@copilot evaluation: 🔴 Not suitable — issue involves work outside the coding agent's capability profile.

Team roster:

Flight (Lead) → label: squad:flight
Procedures (Prompt Engineer) → label: squad:procedures
EECOM (Core Dev) → label: squad:eecom
FIDO (Quality Owner) → label: squad:fido
PAO (DevRel) → label: squad:pao
CAPCOM (SDK Expert) → label: squad:capcom
CONTROL (TypeScript Engineer) → label: squad:control
Surgeon (Release Manager) → label: squad:surgeon
Booster (CI/CD Engineer) → label: squad:booster
GNC (Node.js Runtime) → label: squad:gnc
Network (Distribution) → label: squad:network
RETRO (Security) → label: squad:retro
INCO (CLI UX & Visual Design) → label: squad:inco
GUIDO (VS Code Extension) → label: squad:guido
Telemetry (Aspire & Observability) → label: squad:telemetry
VOX (REPL & Interactive Shell) → label: squad:vox
DSKY (TUI Engineer) → label: squad:dsky
Sims (E2E Test Engineer) → label: squad:sims
Handbook (SDK Usability) → label: squad:handbook
Ralph (Work Monitor) → label: squad:ralph
@copilot (Coding Agent) → label: squad:copilot

To reassign, remove the current squad:* label and add the correct one.

Triage: Contributor-submitted tiered history retrieval feature. Hot/cold layer pattern for context management. Assigned to Procedures (agent memory architecture).

🔄 Ralph status: Feature — 2-tier history retrieval. Research done in #686. Subset of #600 (which adds wiki tier). No implementation PR yet.