Add session export/import to jfr-shell

[jbachorik]

Summary

Implements complete session state export/import functionality for jfr-shell, enabling users to:

• Save analysis progress and resume later
• Share analysis sessions with team members
• Create reusable analysis templates
• Document incident investigations

Changes

New Features

• Session Export: Save complete session state to JSON file

  • Export variables (scalars, maps, lazy queries)
  • Export recording information and metadata
  • Export session settings
  • Optional: include cached query results (--include-results)
  • Row limiting to control file size (--max-rows)

• Session Import: Restore previously exported sessions

  • Recreate all variables and queries
  • Path remapping for cross-machine sharing (--remap-path)
  • Custom alias assignment (--alias)
  • Pre-populate cached results if included in export

Implementation

• SessionSnapshot.java - Immutable data model for session state (~200 lines)
• SessionExporter.java - Export service with JSON serialization (~400 lines)
• SessionImporter.java - Import service with JSON parsing (~500 lines)
• SessionExportImportTest.java - Integration tests (2 tests, all passing)

Commands

# Export
export [--include-results] [--max-rows N] [--format json] <path>

# Import  
import [--alias NAME] [--remap-path PATH] <session-file>

Integration

• Added export/import commands to CommandDispatcher
• Updated tab completion (CommandCompleter, OptionCompleter)
• Comprehensive help documentation (help export, help import)

Documentation

• Updated README.md with feature overview and examples (~100 lines)
• Updated jfr-shell-tutorial.md with detailed use cases (~140 lines)
• Updated jfr_shell_usage.md with command reference
• Updated CLAUDE.md with feature description

Test plan

• Unit tests for SessionSnapshot serialization
• Integration tests for export/import roundtrip
• Manual testing with various variable types
• All existing tests passing
• Code formatting applied (spotless)

Testing checklist

Tested scenarios:

• Export session with scalar, map, and lazy variables
• Import session and verify variables restored
• Export with --include-results option
• Import with --alias option
• Import with --remap-path for different file location
• Export/import with session settings preserved
• Handle missing recording file on import
• Tab completion for export/import commands

Example usage

# Save analysis
jfr> open recording.jfr --alias analysis
jfr> set threshold = 1000
jfr> set bigReads = events/jdk.FileRead[bytes>${threshold}]
jfr> export my-analysis.json

# Resume later
jfr> import my-analysis.json
jfr> vars  # All variables restored
jfr> show ${bigReads}

Future enhancements (Phase 2)

• Markdown export format
• HTML export format with interactive tables
• Command history capture and replay
• Bookmarks and annotations
• Improved JSON parsing with proper library

Notes

• Phase 1 implements JSON format only (Markdown/HTML in Phase 2)
• Simplified JSON parsing sufficient for current needs
• Format version 1.0 with backward compatibility support

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[github-actions]

Combined JUnit Test Report

• Total: 1955
• Passed: 1939
• Failures: 0
• Errors: 0
• Skipped: 16

HTML Test Reports

Run artifacts: https://github.com/btraceio/jafar/actions/runs/33555098506

• JDK 8: HTML report artifact
• JDK 21: HTML report artifact

[jbachorik]

Rebased this PR onto current main and diagnosed the original JDK 21 CI failure.

Rebase: jb/sessions was 8 months stale (branched 2026-01-09, base 2249e07). Rebased cleanly onto main (bc55bd5) with a few conflicts from the shell-core module split that happened in between:

• CLAUDE.md now redirects to AGENTS.md; moved this PR's feature description there instead of reviving the old file.
• CommandDispatcher.java / OptionCompleter.java: merged import lists and option-completion entries added independently on both sides.
• API drift from the module split (SessionManager/Session became generic to support pprof/hprof, LazyQueryValue moved out of VariableStore, getAvailableEventTypes() renamed to getAvailableTypes()): updated SessionExporter, CommandDispatcher, and SessionExportImportTest to match.

JDK 21 failure diagnosis: the CI matrix only runs spotlessCheck on the JDK 21 leg (JDK 8 excludes it explicitly). This PR's new files (SessionImporter.java and SessionExportImportTest.java) had formatting violations — an unused same-package import and two lines exceeding the wrap width — that spotlessCheck would have caught but were never run through spotlessApply before the original push. That's the most likely root cause of the original JDK 21 job failing while JDK 8 passed (JDK 8 doesn't run that check). Ran spotlessJavaApply to fix.

Verification: :jfr-shell:compileJava, :jfr-shell:compileTestJava, and spotlessJavaCheck all pass. Ran the full :jfr-shell:test suite (719 tests, 84 classes) — 56 classes pass cleanly; the other 28 fail solely because this sandbox can't reach Dropbox to fetch the binary JFR test fixtures (test-ap.jfr/test-jfr.jfr/test-dd.jfr, egress-blocked here), confirmed by tracing every failure back to that same missing-file cause. The new SessionExportImportTest itself passes (its two tests self-skip gracefully when the fixture is absent, by design). Note: spotlessGroovy couldn't be verified here either (same network restriction, unrelated dependency), so worth a final CI run to confirm the Groovy build-script formatting is untouched.

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