harness: unify agent + manager prompts into single template (closes #519)

docs/agent-hierarchy.md

@@ -156,9 +156,12 @@ in `migrate.rs` (idempotent, marker-guarded).
 
 ### E — prompt + tools
 
-- `prompts/manager.md` vs `prompts/agent.md` — two separate system
-  prompts. **Per-agent cap list** of what the agent can do, rendered
-  into a single parametrised prompt at boot.
+- `prompts/system.md` with `<!-- role:agent -->` / `<!-- role:manager -->`
+  marker blocks, assembled by `hive_ag3nt::prompt::render` based on
+  flavor (closes #519). **Per-agent cap list** of what the agent can
+  do — already a single parametrised prompt; once #513 lands the
+  marker grammar grows `cap:<group>` blocks the renderer reads from
+  the per-agent ToolGroup set.
 - `mcp.rs::Flavor::{Agent, Manager}` controls which MCP tools claude
   sees. Already structured this way internally — the per-flavour
   allow-list becomes a per-cap-set lookup.

docs/approvals.md

@@ -360,7 +360,8 @@ updates the manager itself.
 
 ## Manager policy
 
-From `hive-ag3nt/prompts/manager.md`: the manager does NOT
+From `hive-ag3nt/prompts/system.md` (`<!-- role:manager -->` block,
+rendered via `hive_ag3nt::prompt::render`): the manager does NOT
 rubber-stamp sub-agent config requests. It verifies (role match,
 package legitimacy, cheaper alternative, blast radius) before
 committing and calling `request_apply_commit`.
@@ -447,7 +448,8 @@ regular claude turn so the manager can react. Variants
   asker sees the matching `QuestionAnswered`.
 
 To add a new event: new `HelperEvent` variant + call sites + update
-`prompts/manager.md` so the manager knows the new shape.
+`prompts/system.md` (`<!-- role:manager -->` block, the lifecycle-
+event list) so the manager knows the new shape.
 
 ## Auto-update on startup
 

docs/turn-loop.md

@@ -163,11 +163,14 @@ socket at `/run/hive/` once at startup:
 - `claude-settings.json` — the `--settings` blob (auto-compact and
   auto-memory off, effortLevel medium).
 - `claude-system-prompt.md` — rendered from
-  `hive-ag3nt/prompts/{agent,manager}.md` with `{label}` and
-  `{operator_pronouns}` substituted. Pronouns come from
-  `HIVE_OPERATOR_PRONOUNS` env (set by the meta flake from
-  `services.hive-c0re.operatorPronouns`, default `she/her`).
-  Passed via `--system-prompt-file`.
+  `hive-ag3nt/prompts/system.md` by `hive_ag3nt::prompt::render`:
+  HTML-comment markers (`<!-- role:agent -->...<!-- /role:agent -->`,
+  same for `role:manager`) gate the role-specific blocks (closes
+  #519); everything else is shared. Then `{label}` and
+  `{operator_pronouns}` get substituted in the assembled output.
+  Pronouns come from `HIVE_OPERATOR_PRONOUNS` env (set by the meta
+  flake from `services.hive-c0re.operatorPronouns`, default
+  `she/her`). Passed via `--system-prompt-file`.
 
 The shared per-turn plumbing lives in `hive_ag3nt::turn::{write_mcp_config,
 write_settings, write_system_prompt, run_turn, drive_turn,