docs: add the Track C findings to the agent guide

Track C finished: 13 of 16 implementation attempts passed. Its report
proposed three more changes, applied here:

- Codex opened the agent guide in 1 of 8 attempts. The README now
  names the agent guide at the start of Installation.
- One attempt computed expiry from the clock in a query, so a hold
  read as released before the reminder ran. The agent guide now says
  that a reminder changes state only when it runs and that a query
  must read the committed state.
- The current-release note now also appears where Track C pointed.

Author: cardmagic

CHANGELOG.md

@@ -2,6 +2,9 @@
 
 ## Unreleased
 
+- The README names the agent guide at the start of Installation, and the agent
+  guide says that a reminder changes state only when it runs under
+  `solid_objects start`, so a query must not compute expiry from the clock.
 - `docs/agents.md` now tells agents to install the current release instead of
   a remembered version, says that step 5 is required before the first call,
   shows the two arguments of `reject`, and lists four API mistakes from

README.md

@@ -44,7 +44,8 @@ And so much more.
 
 ## Installation
 
-Solid Objects requires Ruby 3.3 or newer and Rails 7.1 or newer.
+Solid Objects requires Ruby 3.3 or newer and Rails 7.1 or newer. Coding agents
+should follow the [agent guide](docs/agents.md), which gives each step in order.
 
 ```bash
 bundle add solid_objects

docs/agents.md

@@ -166,6 +166,9 @@ Obey these rules in actor code:
   write in the same database.
 - Do not call an external API in a handler. Use `emit` and an effect handler.
 - Write each handler so that it can run again. Delivery is at least once.
+- A reminder changes state only when it runs, and it runs only while
+  `solid_objects start` runs. Do not compute expiry from the clock in a query;
+  read the state that the reminder committed.
 
 Avoid these mistakes:
 

examples/quickstart/README.md

@@ -46,6 +46,9 @@ bin/rails db:migrate
 bin/rails solid_objects:doctor
 ```
 
+`bundle add solid_objects` installs the current release. Do not pin an older
+version from memory; the API changed between releases.
+
 The generator writes `config/initializers/solid_objects.rb` and copies the
 migrations. The migrations add the Solid Objects tables to the application's
 existing database.