Context hygiene at insert time: result ids, read stubs, the cap, recall

Harness spec 3.0.0 (context.md, loop.json `context`), in session/results.ts,
applied by the engine when a result goes into the conversation and never
afterwards:

- every result is headed by its id ([#0001]); a read also by the path as
  given, its lines, the file's length and the first 8 hex digits of the
  content's SHA-256; an empty file says so;
- a read of an unchanged file whose lines lie inside an earlier full read is
  a stub naming it; a list/glob/grep repeated with the same arguments and the
  same result is "Same result as #…";
- output over 400 lines or 40,000 characters keeps head and tail with the
  elided line; the full result is kept with the session (a new `results`
  table in sessions.db, gone with the session);
- edit, multiedit, write and apply_patch answer with their hunks under a
  bracket with the new content's hash; a new file is "Created, N lines.";
- recall (new built-in tool) shows any stored result, or a range of it, also
  after a resume; ids are never reused;
- compaction appends the table of the reads still in the conversation to the
  summary.

A stub only ever points at a result still in the conversation, so after a
compaction, an /undo or a rewind the file is read in full. compaction.prune
is gone: cutting old outputs in place threw the prompt cache away (an old
config's key is dropped with a warning). blocks/context.md is in the prompt
wherever recall is offered. Conformance runner for the `context` area (11
cases pass).

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

src/config/schema.ts

@@ -276,7 +276,7 @@ export const Config = z.strictObject({
     })
     .optional(),
   question: z.strictObject({ unattended: z.enum(["recommended", "first", "fail"]).optional().describe("With nobody to answer (headless): take the recommended option, the first, or fail.") }).optional(),
-  compaction: z.strictObject({ auto_at: z.number().min(0.1).max(1).optional(), prune: z.boolean().optional() }).optional().describe("Automatic context management: past auto_at of the window, old tool outputs are pruned, then the conversation is compacted. auto_at: 1 turns it off."),
+  compaction: z.strictObject({ auto_at: z.number().min(0.1).max(1).optional() }).optional().describe("Automatic context management: past auto_at of the window, the conversation is compacted. auto_at: 1 turns it off. (Old tool outputs are never cut afterwards: that would make the server read the whole conversation again.)"),
   instructions: z.string().max(4000).optional().describe("Custom instructions: how you want to be helped, in your own words (at most 4000 characters). Appended near the end of the system prompt, under \"## How the person you are talking to wants to be helped\" — as in the LLeMbas web UI. (A list of files here, from an older config, is read as instruction_files.)"),
   instruction_files: z.array(z.string()).optional().describe("More instruction files for the system prompt, besides AGENTS.md / CLAUDE.md."),
   search: z