Shorten the idea to its three claims

[andreisavu]

"The idea" ran 39 lines and 307 words before a reader met a function name.
It is 22 lines and 189 words now, and it makes the same three claims.

What was doubled

Each claim had a paragraph and a three-bullet list under it, and the
bullets restated the paragraph above them.

• "Cost follows events" and "An idle session costs nothing" were two
  bullets for one fact.
• "Inside one agent every technique serves the same domain, so the
  techniques compose" restated the sentence above it.
• "Agents with owners, working in a workspace built for collaboration"
  restated "Ambion makes the team first-class".

The bullets are gone and the paragraphs hold anything they added. A reader
of the three bold leads still gets the section's claims, which is what the
writing guidance asks of a page.

What stayed

Both framings, as CLAUDE.md requires: agents wait for events, and the
agent is the ownership boundary.

• Agents should wait for events. Unchanged in substance.
• The agent is the ownership boundary. The lead was "the unit of
  context engineering, and the ownership boundary"; the sentence under it
  makes the first half, so the lead names the boundary. The step from a
  shared context window to an agent no team can improve is one sentence
  now, and it keeps the argument the claim rests on.
• Every agent that keeps growing arrives at multi-agent collaboration.
  The lead dropped "Ambion starts there", which the paragraph says.

Also

Two sentences ran to 26 words against the 25 the writing rules allow for a
description. One of them predates this change. Both are two sentences now.

Checks

pnpm run check:format passes. The change is one section of README.md,
so no code, test or contract moved.