feat(mar-887): shared agent SDK file inside the agent folder

[Thebeatkicks]

Stage 1 of MAR-886. There were two copies of the agent runtime and no shared
module; ADR 0032 recorded the fork as a later packet's job, and this is that
packet.

What this is

agent-kit/template/dash-agent-sdk.mjs is the runtime as one self-contained ESM
file — node builtins only, no package, no node_modules — that ships inside
the agent folder beside agent.mjs and is imported from it by relative path.
Both scaffolders and the packaged sample write the same bytes.

The templates keep their definition and their task logic and nothing else:
agent-kit/template/agent.mjs goes from 1060 lines to 554,
tools/dash-mcp/template/agent.mjs from 743 to 416. brief-fingerprint.mjs is
absorbed into the runtime, which already carried the same do not edit warning;
DASH's half stays at lib/brief/fingerprint.ts and the mirror test still pins
the two halves against each other.

Why a file rather than a dependency

agent-kit/scaffold.ts writes dependencies: {} on purpose, and the packaged
sample is copied as raw bytes into the user's Documents folder by
scripts/build-shell.mjs. There is no install step anywhere in the installed
journey and no place to put one a person would forgive. Bundling the runtime
into agent.mjs at scaffold time was the other candidate and destroys the
property the split exists for: a runtime fix that reaches an agent somebody has
been editing for months without touching their file. ADR 0034 has both
arguments.

Nothing the runner sees changed

Same seven telemetry types at event_version: 1, the same seq/ts
discipline, the same artifact shapes at versions 1 and 2, the same four
acknowledged commands, the same waiting task. The one place a shape could have
moved — the digest's generated_at, which one template stamped and the other
did not — is resolved by stamping it only when the author did not, so both
templates emit the same keys in the same order they did before.

Old agents are untouched and keep working: ADR 0008 makes the folder the unit
and nothing rewrites agent.mjs in place, so every agent generated before this
is still monolithic and spawned by a runner that did not change.
tests/legacy-agent.test.ts spawns those exact bytes (cb2cb1c, kept at
tests/fixtures/legacy-agent-kit-template.mjs) under a real Supervisor.

Verified

• pnpm typecheck clean.
• pnpm test — 283 files, 5352 passed, 13 skipped, 0 failed.
• pnpm build:agent-kit, then the real CLI: a scaffold on disk carrying
  agent.mjs and dash-agent-sdk.mjs.
• pnpm build:renderer; pnpm build:shell — dist/electron/agent-kit/ holds
  both files.
• The installed-style shell smoke on a scratch store: 85 PASS / 0 FAIL,
  [smoke] all proofs passed. 6b lists dash-agent-sdk.mjs in the handoff
  DASH creates, 6c-f shows code/dash-agent-sdk.mjs accepted with its hash
  into DASH's own stored copy, and 6d–6k are the acceptance sentence run
  against a real generated agent through the SDK: it waits to be asked, nothing
  runs on its own, Run now goes through the audited bridge, telemetry renders
  compliant: true with no sequence gap, and the digest reaches both the folder
  and DASH. Runner retired with scripts/retire-scratch-runners.mjs (202).

Evidence class: fixture tests plus an installed-style shell on a scratch store.
The real store was never opened; the installed-build proof is the orchestrator's.

docs/foundation/stage-1-handoff.md carries the deviations, what is not done,
and what the next session should read first.

🤖 Generated with Claude Code