nes-datagen: add cursor-jump (NCLP) sample task

[ulugbekna]

Extends nes-datagen to generate training data for the cursor-jump
(next-cursor-line) prediction model alongside the existing xtab path.

CLI

A new --sample-task flag selects what to generate:

value	what it emits
xtab (default)	unchanged xtab samples
cursor-same-file	cursor-jump samples where the jump stays in the active file
cursor-cross-file	cursor-jump samples where the jump goes to another file
cursor-both	both of the above

Same-file detection is gated by --same-file-jump-min-above (default
2) and --same-file-jump-min-below (default 5); a recording is
only used if the post-bookmark cursor lands farther than that window
from the request-time cursor.

How it works

The datagen path reuses the production XtabNextCursorPredictor to
build the prompt drift between datagen and production wouldverbatim
corrupt the training distribution. The prompt is captured via a
no-op fetcher + telemetry builder; the expected response is built by
pure detector / formatter modules from the post-bookmark recording.

                  
      DetectedJump detectJump ( pure)                     recording 
 same-file vs cross-file                      
 applies edits in correct                     
    (descending) order                         
                  
                                
            {                 echo ___BEGIN___COMMAND_OUTPUT_MARKER___;                 PS1="";PS2="";unset HISTFILE;                 EC=$?;                 echo "___BEGIN___COMMAND_DONE_MARKER___$EC";             }
                  
 reuses production   cursorJumpPromptStep                          
    XtabNextCursorPredictor ''    
 reads back prompt from                       
    telemetry builder                          
                  
                                
            {                 echo ___BEGIN___COMMAND_OUTPUT_MARKER___;                 PS1="";PS2="";unset HISTFILE;                 EC=$?;                 echo "___BEGIN___COMMAND_DONE_MARKER___$EC";             }
                  
 cursorJumpResponseStep                        
 same-file: keptRange                         
 cross-file: path:line                        
                  

Polish commits

After the feature landed, four follow-up commits address review
feedback:

• replace SAMPLE_TASK_VALUES tuple with a NesDatagenSampleTask
  string enum
  2
  cursor-jump everywhere (files via git mv, ids /
  comments / test descriptions updated)
• pass the whole recording to documentIndexMapping instead of
  slicing then backfilling post-request documentEncountered entries

Tests

68 / 1 npx vitest run test/pipeline. Notable:skipped

• detectJump.spec.ts covers same-file thresholds, cross-file
  resolution, and the (regression-tested) bug where multiple
  changed edits were applied ascending in-place instead of
  descending.
• Typecheck clean: npx tsgo --noEmit --project tsconfig.json in
  extensions/copilot.

[Copilot]

Pull request overview

This PR extends the nes-datagen pipeline (Copilot extension test tooling) to generate training samples for the cursor-jump / next-cursor-line prediction model in addition to the existing xtab (edit prediction) samples. It adds a CLI switch to select the sample task, reuses the production cursor-prediction prompt construction to avoid prompt drift, and introduces pure detector/formatter modules to label expected cursor-jump outputs from post-bookmark recordings.

Changes:

• Add --sample-task (xtab / cursor-same-file / cursor-cross-file / cursor-both) plus same-file threshold flags, and route the pipeline accordingly (including parallel worker argument propagation).
• Implement cursor-jump detection + response formatting (same-file and cross-file) with dedicated unit tests.
• Expose production cursor-prediction prompt construction (buildCursorPredictionPrompt) and capture prompt/kept-range for datagen tooling.

Show a summary per file

File	Description
extensions/copilot/test/pipeline/test/pipeline.spec.ts	Updates pipeline test wiring to pass new nes-datagen options.
extensions/copilot/test/pipeline/test/pipeline.e2e.spec.ts	Updates e2e tests to include new nes-datagen options.
extensions/copilot/test/pipeline/replayRecording.ts	Extends processed-row shape with post-request recording slices + request-time cursor/content snapshots.
extensions/copilot/test/pipeline/pipeline.ts	Adds cursor-jump pipeline path (jump detection → prompt capture → response formatting → sample output).
extensions/copilot/test/pipeline/output.ts	Extends sample metadata with task and optional jump info; threads through assembleSample.
extensions/copilot/test/pipeline/cursorJump/detectJump.ts	Adds pure same-file / cross-file jump detectors + path normalization helper.
extensions/copilot/test/pipeline/cursorJump/detectJump.spec.ts	Unit tests for detectors, normalization, and response formatting.
extensions/copilot/test/pipeline/cursorJump/cursorJumpResponseStep.ts	Formats expected cursor-jump assistant outputs and attaches jump metadata.
extensions/copilot/test/pipeline/cursorJump/cursorJumpPromptStep.ts	Runs production NES pipeline with a no-op fetcher to capture the real cursor-jump prompt and kept range.
extensions/copilot/test/pipeline/alternativeAction/processor.ts	Exposes recording split-at-request logic and broadens doc-id→path mapping to whole recording.
extensions/copilot/test/base/simulationOptions.ts	Introduces NesDatagenSampleTask enum, parses new CLI flags, updates help text.
extensions/copilot/src/platform/inlineEdits/common/statelessNextEditProvider.ts	Adds fields intended for debug/datagen access to cursor-jump prompt data.
extensions/copilot/src/extension/xtab/node/xtabNextCursorPredictor.ts	Exports cursor-jump system prompt and factors out prompt construction (buildCursorPredictionPrompt).
extensions/copilot/src/extension/inlineEdits/node/nextEditProviderTelemetry.ts	Adds a getter for accessing stored stateless telemetry on the NES telemetry builder.

Copilot's findings

• Files reviewed: 14/14 changed files
• Comments generated: 2

[ulugbekna]

• have you added tests similar to what we have for the xtab samples?

[ulugbekna]

I don't like this being called entries -- it should be "wholeRecording"

[ulugbekna]

this looks like it couldn't been inlined?

[ulugbekna]

I wonder if having a union type to avoid optional fields would be a better engineering decision here.