docs(prompt): align precedence docs with system prompt runtime

- Replace outdated linear ordering in prompt-assembly guide with
  current stable/context/volatile tier contract from system_prompt.py
- Clarify where memory/profile snapshots live versus skills guidance
- Document that pre_llm_call context is user-message injection, not
  cached system-prompt mutation
- Update architecture guide wording to reference system_prompt.py +
  prompt_builder.py tiered assembly

Closes #34118

website/docs/developer-guide/architecture.md

@@ -197,7 +197,7 @@ The synchronous orchestration engine (`AIAgent` in `run_agent.py`). Handles prov
 
 Prompt construction and maintenance across the conversation lifecycle:
 
-- **`prompt_builder.py`** — Assembles the system prompt from: personality (SOUL.md), memory (MEMORY.md, USER.md), skills, context files (AGENTS.md, .hermes.md), tool-use guidance, and model-specific instructions
+- **`system_prompt.py` + `prompt_builder.py`** — assembles the ordered system-prompt tiers (`stable` → `context` → `volatile`): identity/tool guidance/skills, context files, then memory/profile/timestamp blocks
 - **`prompt_caching.py`** — Applies Anthropic cache breakpoints for prefix caching
 - **`context_compressor.py`** — Summarizes middle conversation turns when context exceeds thresholds
 

website/docs/developer-guide/prompt-assembly.md

@@ -26,18 +26,18 @@ Primary files:
 
 ## Cached system prompt layers
 
-The cached system prompt is assembled in roughly this order:
+The cached system prompt is assembled as three ordered tiers (see `agent/system_prompt.py`):
 
-1. agent identity — `SOUL.md` from `HERMES_HOME` when available, otherwise falls back to `DEFAULT_AGENT_IDENTITY` in `prompt_builder.py`
-2. tool-aware behavior guidance
-3. Honcho static block (when active)
-4. optional system message
-5. frozen MEMORY snapshot
-6. frozen USER profile snapshot
-7. skills index
-8. context files (`AGENTS.md`, `.cursorrules`, `.cursor/rules/*.mdc`) — SOUL.md is **not** included here when it was already loaded as the identity in step 1
-9. timestamp / optional session ID
-10. platform hint
+1. **stable** — identity (`SOUL.md` or fallback), tool/model guidance, skills prompt, environment hints, platform hints
+2. **context** — caller-supplied `system_message` plus project context files (`.hermes.md` / `AGENTS.md` / `CLAUDE.md` / `.cursorrules`)
+3. **volatile** — built-in memory snapshot (`MEMORY.md`), user profile snapshot (`USER.md`), external memory-provider block, timestamp/session/model/provider line
+
+The final system prompt is then joined as: `stable` → `context` → `volatile`.
+
+This ordering matters for precedence discussions:
+- skills are part of the **stable** tier
+- memory/profile snapshots are part of the **volatile** tier
+- both are still in the cached system prompt (they are not injected as ad-hoc mid-turn overlays)
 
 When `skip_context_files` is set (e.g., subagent delegation), SOUL.md is not loaded and the hardcoded `DEFAULT_AGENT_IDENTITY` is used instead.
 
@@ -205,13 +205,15 @@ These are intentionally *not* persisted as part of the cached system prompt:
 - `ephemeral_system_prompt`
 - prefill messages
 - gateway-derived session context overlays
-- later-turn Honcho recall injected into the current-turn user message
+- later-turn Honcho/external recall injected into the current-turn user message
+
+`pre_llm_call` plugin context also lands in this API-call-time path: it is appended to the current turn's **user message**, not written into the cached system prompt. When multiple plugins return context, Hermes concatenates those context blocks (see [Hooks → `pre_llm_call`](../user-guide/features/hooks.md#pre_llm_call)).
 
 This separation keeps the stable prefix stable for caching.
 
 ## Memory snapshots
 
-Local memory and user profile data are injected as frozen snapshots at session start. Mid-session writes update disk state but do not mutate the already-built system prompt until a new session or forced rebuild occurs.
+Local memory and user profile data are captured in the system prompt's **volatile tier**. Mid-session writes update disk state but do not mutate the already-built cached system prompt until a rebuild path runs (new session, or explicit invalidation/rebuild flow such as compression-triggered rebuild).
 
 ## Context files