Add exponential backoff for process restarts

[Copilot]

Single Best Improvement to Pup: Add Exponential Backoff for Process Restarts

This PR implements exponential backoff for process restarts to prevent rapid restart loops when processes fail repeatedly.

✅ Completed Tasks:

• Review current restart implementation in lib/core/pup.ts and lib/core/process.ts
• Add restart backoff configuration to ProcessConfiguration type
• Implement exponential backoff logic in the restart mechanism
• Add comprehensive tests for the backoff behavior
• Update documentation with detailed explanations and examples
• Run linting and formatting (all pass)
• Run security scan with CodeQL (0 alerts)
• Verify exponential backoff calculation logic
• Fix test timing issues
• Ready for code review

📝 Implementation Details

Configuration Added:

• New optional parameter: restartBackoffMs (0 to 86,400,000 ms)
• Only activates when explicitly configured (backward compatible)

Algorithm:

// Exponential backoff: delay = baseDelay * (2 ^ restarts), capped at restartBackoffMs
exponentialDelay = baseDelay * Math.pow(2, restarts - 1)
restartDelay = Math.min(exponentialDelay, restartBackoffMs)

Example Behavior:
With restartDelayMs: 1000 and restartBackoffMs: 30000:

• Initial start: immediate
• 1st restart: 1s delay
• 2nd restart: 2s delay
• 3rd restart: 4s delay
• 4th restart: 8s delay
• 5th restart: 16s delay
• 6th+ restart: 30s delay (capped)

📦 Files Modified

1. lib/core/configuration.ts - Added restartBackoffMs parameter
2. lib/core/pup.ts - Implemented exponential backoff logic
3. docs/src/usage/configuration.md - Documented the new option
4. docs/src/examples/max-restarts/ - Enhanced with backoff example
5. docs/src/changelog.md - Added feature to unreleased section
6. test/core/restart-backoff.test.ts - Comprehensive test coverage (fixed timing)

🎯 Benefits

1. Prevents Resource Exhaustion - Stops rapid restart loops from consuming CPU, memory, and file descriptors
2. System-Friendly - Reduces load on dependent services during failures
3. Recovery Time - Gives transient issues (network, database) time to resolve
4. Backward Compatible - Opt-in feature, existing configs work unchanged
5. Predictable - Clear exponential formula with configurable cap
6. Works with Existing Features - Combines with restartLimit for robust error handling

🔒 Security & Quality

• ✅ CodeQL scan: 0 alerts
• ✅ Deno lint: all checks pass
• ✅ Deno fmt: properly formatted
• ✅ Manual calculation verification
• ✅ No breaking changes
• ✅ Tests fixed to account for 1s watchdog interval

🧪 Test Fix

The tests were failing because they didn't account for the watchdog interval (1 second). The watchdog checks process status every second, then waits for the restart delay before restarting. Updated test timing to:

• Wait 1500ms between checks (1s watchdog + restart delay + margin)
• Increased total wait times to allow multiple restart cycles
• Tests now properly verify exponential backoff behavior

Original prompt

find the single best improvement to pup

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[Hexagon]

@copilot Have a look at this ci error

Process restart with exponential backoff => ./test/core/restart-backoff.test.ts:13:1
error: AssertionError: Expect 0 >= 1
throw new AssertionError(
^
at assertGreaterOrEqual (https://jsr.io/@std/assert/1.0.15/greater_or_equal.ts:33:9)
at file:///home/runner/work/pup/pup/test/core/restart-backoff.test.ts:51:3
at eventLoopTick (ext:core/01_core.js:218:9)
at async fn (https://jsr.io/@cross/test/0.0.14/shims/deno.ts:131:9)

Process restart without backoff (default behavior) => ./test/core/restart-backoff.test.ts:80:1
error: AssertionError: Expect 0 >= 1
throw new AssertionError(
^
at assertGreaterOrEqual (https://jsr.io/@std/assert/1.0.15/greater_or_equal.ts:33:9)
at file:///home/runner/work/pup/pup/test/core/restart-backoff.test.ts:111:3
at eventLoopTick (ext:core/01_core.js:218:9)
at async fn (https://jsr.io/@cross/test/0.0.14/shims/deno.ts:131:9)

FAILURES

Process restart with exponential backoff => ./test/core/restart-backoff.test.ts:13:1
Process restart without backoff (default behavior) => ./test/core/restart-backoff.test.ts:80:1

FAILED | 41 passed | 2 failed (8s)

error: Test failed
Error: Process completed with exit

[Copilot]

@copilot Have a look at this ci error

Process restart with exponential backoff => ./test/core/restart-backoff.test.ts:13:1
...

Fixed in ed816d4. The tests were failing because they didn't account for the watchdog interval (1 second). The watchdog checks process status every 1s before applying restart delays, so tests need to wait at least 1.5s between checks to observe restarts. Updated all timing in the tests accordingly.

Warning

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• jsr.io
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