feat: session memory bridge — inject and persist context across sessions

[OneStepAt4time]

Summary

Sessions are stateless — each new session starts from zero. A memory bridge would allow sessions to read/write shared context, enabling continuity across related tasks without manual copy-paste of context.

Problem

• Hep works on 3 parallel worktrees. Session A fixes a bug in webhook.ts, Session B needs to know about that fix to avoid conflicts.
• No way to persist learnings from one session to the next (e.g., "this module uses Zod v3.23").
• Currently relies on human (Athena/Ema) manually providing context via prompt — error-prone and slow.

Proposed API

• POST /v1/memory — write key/value entry with optional TTL and session scope
• GET /v1/memory/:key — read entry (latest value or merged history)
• GET /v1/memory?prefix=webhook.* — list entries by key prefix
• DELETE /v1/memory/:key — remove entry
• Auto-inject: session creation accepts memoryKeys: string[] → bridge injects values into system prompt

Storage

• Default: in-memory Map with optional JSON file persistence
• Key structure: namespace/key (e.g., session/abc123/context, global/project-structure)
• TTL support for auto-expiry

Acceptance Criteria

• Memory bridge module (src/memory-bridge.ts)
• REST API endpoints for CRUD
• Auto-injection into session system prompt via memoryKeys
• TTL support with auto-expiry
• JSON file persistence option
• Tests for read/write/expiry/injection
• Backward compatible (disabled by default, opt-in via config)

Priority

P1 — foundational for multi-session workflows and v2.5.0 roadmap

References

• feat: session memory store — persist and share context between sessions #748 (session memory store — P1)
• feat: session memory persistence and injection #751 (session memory persistence — P3, Hep's version)
• OMC: src/features/context/ — context injection patterns
• CC: CLAUDE.md auto-injection on session start

[OneStepAt4time]

🔧 Starting work on this. Approach: in-memory Map + JSON file persistence, REST API (POST/GET/DELETE /v1/memory), TTL support, auto-inject via memoryKeys config. Worktree: feat/783-memory-bridge. ETA: ~45 min.

[OneStepAt4time]

✅ PR #951 opened. Core module + tests done. Routes and injection coming in follow-up. CI green. CC got stuck twice — fell back to direct implementation.

[OneStepAt4time]

✅ PR #951 merged. Core module done. Routes + session injection in follow-up PR.