Harness spec 3.0.0-draft: prompts, the link, and the changelog

blocks/context.md tells the model about stubs and recall; blocks/workspace.md
tells a chat's model its view. blocks/library.md and blocks/prototypes.md are
the CLI's alone. acp.md: `instance` on session/new, a client-opened session
runs on the chat's model and no other (the own-model notice is gone),
capability `show` with `_lembas/show`, memory through the instance. README:
the new fields and the 3.0.0 section. VERSION 3.0.0-draft.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

harness/prompts/blocks/context.md

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+<!-- LLeMbas CLI and LLeMbas, spec 3.0.0: how tool results are kept short (context.md). -->
+# Tool results
+- Every tool result starts with its id in brackets, like `[#a3f2]`. A read's bracket also says the path, the lines shown, the file's length and a short hash of its content: `[#a3f2 src/app.ts lines 1-200 of 340 sha 1c9e04ab]`.
+- Reading a file that has not changed since an earlier read in this conversation returns a stub instead of the lines: `Unchanged since #a3f2, which already shows lines 1-200.` The content is in that earlier result. Use it; do not read the file again to see it.
+- A listing or search repeated with the same result returns `Same result as #f001.` in the same way.
+- Long output is shortened to its beginning and its end, with `[1234 lines elided, full output #c9d0]` between them.
+- `recall` with an id shows that stored result in full, or from a line on: for lines left out of a shortened output, or for a result from before the conversation was summarised. Nothing is lost; recall only what you need.
+- An edit answers with the diff of the change, not the whole file. The earlier read with that diff applied is the file now: read it again only for lines you have not seen.
+- After the conversation is summarised, earlier results are no longer in front of you. The summary ends with a table of the files read before it, with their ids; a file read again then comes back in full.