deepseek-harness/.agents/notes/implemented/architecture/2026-07-29-dsh-source-launch-tsx-esm.md

Agent Note: dsh source launch through the tsx ESM hook

Status: implemented

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Supersedes native TypeScript source launch: Node removed the capability that decision was built on.

Problem

The archived native source-launch decision ran apps/cli/src/bin.ts under node --experimental-transform-types with a resolve-only paths loader, so Node owned TypeScript transformation. Node 26.0.0 removed --experimental-transform-types (the process rejects the flag with bad option), keeping only strip mode, and strip mode rejects syntax this source graph requires: vendored Cordis parameter properties (constructor(private ctx: Context)), the @Inject decorators in vendor/hmr, and runtime enums/namespaces throughout vendor/ and packages/workflow. The repository's engines range (^22.19.0 || >=24.0.0) includes Node 26, so the native launch chain could not start at all there — and no CI job executed the real launch vector, so the incompatibility shipped silently.

Startup latency also mattered: the off-thread module.register() hooks worker serialized every resolution across threads (~440ms of makeSyncRequest wait during TUI boot), and the full tsx default (--import tsx) pays ~0.4s in its CJS hook's resolution amplification.

Decision

The dsh TUI, Web, and headless source launches run node --import tsx/esm: tsx's ESM-only hook owns both TypeScript transformation and tsconfig paths projection. The root dsh script uses that vector directly from the repository root; artifact generation is a separate operation under the source-launch/build separation decision. The CJS hook stays off because the CLI source graph is ESM-only; measured runtime launch to the TUI banner is ~0.7s versus ~1.1s under the full tsx default and ~0.75s under the removed native chain.

scripts/tspath-loader.ts and apps/cli/src/tsconfig-paths-loader.ts are deleted. With them went the loader's runtime rule of mapping a workspace import only for declared runtime dependencies — tsx applies the paths map unconditionally. Declaration completeness now rests on the static gates alone: verify-cordis-config for configured bare plugins, and workspace constraints for manifests. (That runtime rule found real bugs: dsh-plan-mode and dsh-tool-jobs imported @deepseek-ai/dsh-llm while declaring it only in devDependencies; since fixed.)

The node-compat CI matrix (Node 22.19 and 26) gains dsh-source-launch-smoke (apps/cli/tests/source-launch.compat.spec.ts): a keyless piped-stdio launch of the exact production runtime vector asserting the non-zero-exit TTY refusal. Any future Node change to module hooks or TypeScript handling turns this gate red instead of breaking developers' pnpm dsh.

Alternatives considered

Keep the native chain on Node ≤25 and branch by version. Rejected: two transformation semantics (amaro versus esbuild) diverge on edge syntax, the launcher grows version probing, and the node-compat matrix must cover both paths — heavy maintenance for an experimental flag that already changed under us. amaro also rejects the @Inject decorators vendor/hmr uses, so the native path could not boot the shipped default TUI config anyway.

Make the source graph erasable-only so Node 26 strip mode accepts it. Rejected: parameter properties and value namespaces pervade vendored Cordis/cosmokit/loader/schemastery; rewriting them is unbounded churn re-applied on every vendor sync.

A repo-owned in-thread loader (module.registerHooks() plus an esbuild or @swc/core transform). Rejected: prototypes measured about 0.45s, while the esbuild path lacked end-to-end validation and SWC failed on vendor/hmr's decorator plus namespace merge in both decorator modes. This option also makes the repository own transform correctness and a resolve hook that tsx already provides. Revisit only if the measured 0.3s gap becomes a material cost.

Run built lib/ for Node 26 and keep native for 24. Rejected: loses the zero-build development loop on the newest Node line and mixes source and artifact planes.

Consequences

• One launch vector across the whole engines range, including future Node lines that change native TypeScript support; the smoke gate enforces it per matrix line.
• TypeScript transformation is delegated to tsx/esbuild again, reversing the prior note's goal of proving Node-native transformation; that goal is unreachable while vendored sources use non-erasable syntax and Node ships no transform mode.
• The runtime declared-dependency enforcement in source launches is gone; undeclared workspace imports now surface only through static gates or built-mode resolution failures.
• Runtime launch improves ~0.4s over the full tsx default; ACP keeps --import tsx because its graph was not audited for CJS-hook dependence and its launch latency is not on the interactive path.