fix(durable-functions): route sync single-arg orchestrators to core-native (#321)

[YunchuWang]

Fixes #321.

What

In the compat durable-functions (v4) package, a plain synchronous, single-argument, non-generator orchestrator (ctx) => value is now classified as core-native: it passes through wrapOrchestrator unchanged and receives the core OrchestrationContext directly.

Previously the classifier fell back to arity for plain sync functions — a lone context parameter was treated as classic and handed the { df, log } context. That mis-routed core-native handlers like (ctx) => ctx.instanceId: ctx.instanceId was undefined and members such as ctx.callActivity / ctx.newGuid() threw. That is the bug reported in #321.

Change (minimal)

• src/orchestration-context.ts — isClassicOrchestrator: the plain-sync branch now returns false (core-native) instead of return handler.length <= 1. Only a sync generator (function*) is classic. Updated the wrapOrchestrator doc comment to match.
• test/unit/orchestration-context.spec.ts — the "replay-safe logger on the classic context" test used a plain non-generator classic orchestrator; converted it to the standard function* form (same intent). Added a [durable-functions v4] isClassicOrchestrator can't distinguish a plain sync single-arg core-native orchestrator from a classic one #321 regression test asserting the sync single-arg native handler passes through unchanged (identity).
• README.md / CHANGELOG.md — documented the breaking change.

Behavior matrix

Orchestrator shape	Before	After
function*(ctx) classic (uses context.df.*)	classic	classic (unchanged)
async function*(ctx)	core-native	core-native (unchanged)
async (ctx) => …	core-native	core-native (unchanged)
(ctx, input) => … (arity 2)	core-native	core-native (unchanged)
(ctx) => … sync single-arg	classic (arity fallback)	core-native (fixes #321)

⚠️ Breaking change

A classic v3 orchestrator written as a plain non-generator function using context.df.* in this exact shape (sync, single-arg, non-generator) no longer receives the classic context. Convert it to the standard classic generator form (function*, unaffected) or to the core-native ctx.* API. Standard function* classic orchestrators — the normal v3 shape — are unaffected. Documented under "Migrating from durable-functions v3" in the package README and in the CHANGELOG.

Validation

• npm run build:core → exit 0
• npm run build -w durable-functions → exit 0
• Full compat unit suite: 15 suites / 103 tests passing

[Copilot]

Pull request overview

This PR fixes durable-functions (v4 compat) orchestrator classification so a plain synchronous, single-argument, non-generator handler (ctx) => value is treated as core-native and receives the core OrchestrationContext (fixing #321), rather than being misrouted to the classic { df, log } context via an arity fallback.

Changes:

• Updated isClassicOrchestrator to classify only sync generators (function*) as classic; plain sync functions now always pass through as core-native.
• Updated unit tests to reflect the classic orchestrator “generator” ground truth and added a regression test for #321 asserting identity passthrough for (ctx) => ....
• Documented the resulting breaking change in the package README and CHANGELOG.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
packages/azure-functions-durable/src/orchestration-context.ts	Removes arity fallback for plain sync functions; only function* is treated as classic.
packages/azure-functions-durable/test/unit/orchestration-context.spec.ts	Updates classic logger test to use function* and adds #321 regression test for sync single-arg core-native passthrough.
packages/azure-functions-durable/README.md	Documents breaking change for plain non-generator “classic” orchestrators.
packages/azure-functions-durable/CHANGELOG.md	Records behavior change and breaking-change guidance for consumers.

[Copilot]

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

[Copilot]

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated no new comments.

[Copilot]

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated no new comments.

[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

Comments suppressed due to low confidence (1)

packages/azure-functions-durable/src/orchestration-context.ts:224

• After this change, plain sync non-generator handlers are always core-native, so a classic orchestrator must be a function* generator. However, the exported ClassicOrchestrator type still allows a classic handler to be a plain non-generator function (it includes | unknown), which no longer matches runtime behavior and may mislead TS consumers.

 *   the wrapper delegates to it via `yield*`.
 * - A plain SYNC (non-generator) function is CORE-NATIVE regardless of arity and passes through
 *   unchanged, receiving the core {@link OrchestrationContext}. This fixes #321 (a native
 *   `(ctx) => ctx.instanceId` previously mis-routed by arity to the classic context). BREAKING: a
 *   classic v3 orchestrator written as a plain non-generator using `context.df.*` is no longer