Fix code review findings: timestamps, error handling, tests, docs

[umputun]

Bug fixes:

• Fix incorrect timestamp calculations in events.go — Time was divided by 1000 (already Unix seconds), TimeNano was misused as sub-second offset instead of full nanosecond timestamp. Added fallback for older Docker API versions where TimeNano may be zero
• Fix syslog writer double-close when both files and syslog enabled — same syslogWriter was added to both log and err MultiWriter slices, getting Close() called twice. Fixed with writeNopCloser wrapper on the err copy
• Fix typo "even listener" → "event listener" in events.go
• Add guard for empty c.Names slice in emitRunningContainers()

Error handling improvements:

• Replace log.Fatalf in makeLogWriters with proper error returns — signature changed to (logWriter, errWriter io.WriteCloser, err error), callers handle gracefully
• Add missing filter validation: IncludesPattern + ExcludesPattern, Includes + ExcludesPattern, IncludesPattern + Excludes combinations now rejected
• Extract duplicated stream cleanup logic into closeStreamWriters helper in runEventLoop

Code quality:

• Fix variable shadowing in MultiWriter.Write and Close — loop variable w shadowed receiver

Test reliability:

• Replace flaky time.Sleep patterns with require.Eventually and channel-based synchronization across main_test.go and logger_test.go
• Improve syslog test quality with actual UDP listener verification
• Add MixErr coverage for runEventLoop
• Add timestamp validation tests, error path tests for makeLogWriters

Documentation:

• Add missing CLI flags to README: --loc/LOG_FILES_LOC, --syslog-prefix/SYSLOG_PREFIX, --dbg/DEBUG
• Add --exclude/--exclude-pattern mutual exclusivity note to README
• Fix README typo "inlcudes" → "includes"
• Improve godoc for GetWriter, LogStreamer.Go(), Close(), Wait()
• Update CLAUDE.md with makeLogWriters signature change and writeNopCloser pattern

[coveralls]

Pull Request Test Coverage Report for Build 22087845807

Details

• 94 of 106 (88.68%) changed or added relevant lines in 4 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage increased (+3.9%) to 79.339%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
app/discovery/events.go	24	27	88.89%
app/main.go	58	67	86.57%

Files with Coverage Reduction	New Missed Lines	%
app/main.go	1	84.16%

Totals
Change from base Build 22058265196:	3.9%
Covered Lines:	384
Relevant Lines:	484

---

💛 - Coveralls

[Copilot]

Pull request overview

This PR addresses a set of issues found during a full-project code review, focusing on correctness (timestamps, writer lifecycle), improved error handling, more reliable tests, and updated documentation.

Changes:

• Fix Docker event timestamp handling (including TimeNano fallback) and add guards/tests for edge cases in discovery.
• Replace fatal exits in makeLogWriters with error returns; harden writer lifecycle (syslog double-close) and improve validation.
• Reduce test flakiness by replacing time.Sleep with require.Eventually, and expand syslog + MixErr coverage; update README/godoc/CLAUDE docs accordingly.

Reviewed changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
docs/plans/completed/20260216-code-review-fixes.md	Adds a completed implementation plan/trace for the review-driven fixes.
app/syslog/syslog_unix.go	Clarifies GetWriter godoc re: syslog prefix usage.
app/main_test.go	Removes sleep-based waits; adds sentinel/eventually synchronization; adds new writer/syslog/MixErr tests.
app/main.go	Adds filter/destination validation; changes makeLogWriters to return errors; prevents syslog double-close via writeNopCloser.
app/logger/multiwriter.go	Fixes loop variable shadowing in Write/Close.
app/logger/logger_test.go	Replaces sleeps with require.Eventually to reduce flakiness.
app/logger/logger.go	Improves godoc for Go, Close, and Wait.
app/discovery/events_test.go	Adds timestamp validation and coverage for containers with no names + TimeNano fallback.
app/discovery/events.go	Fixes event listener typo; corrects timestamp calculation and adds guard for empty container names.
README.md	Adds missing CLI flags and documents additional mutual exclusivity rules; fixes one typo.
CLAUDE.md	Documents makeLogWriters signature change and the syslog no-double-close pattern; adds testing guidance.

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[Copilot]

The new README bullets use the misspelling "vise versa". Please change to "vice versa" for correct wording.

Suggested change

	- both `--exclude` and `--include` flags are optional and mutually exclusive, i.e. if `--exclude` defined `--include` not allowed, and vise versa.
	- both `--include` and `--include-pattern` flags are optional and mutually exclusive, i.e. if `--include` defined `--include-pattern` not allowed, and vise versa.
	- both `--exclude` and `--exclude-pattern` flags are optional and mutually exclusive, i.e. if `--exclude` defined `--exclude-pattern` not allowed, and vise versa.
	- both `--exclude` and `--include` flags are optional and mutually exclusive, i.e. if `--exclude` defined `--include` not allowed, and vice versa.
	- both `--include` and `--include-pattern` flags are optional and mutually exclusive, i.e. if `--include` defined `--include-pattern` not allowed, and vice versa.
	- both `--exclude` and `--exclude-pattern` flags are optional and mutually exclusive, i.e. if `--exclude` defined `--exclude-pattern` not allowed, and vice versa.

[Copilot]

This test uses a hard-coded Unix-specific path ("/dev/null/invalid/path") to force a mkdir error. This is not portable (will behave differently on Windows) and can also risk creating real directories on some platforms. Prefer constructing a guaranteed-invalid path using t.TempDir() (e.g., create a file and attempt MkdirAll under it) so the failure is hermetic across OSes.

Suggested change

	opts := cliOpts{EnableFiles: true, FilesLocation: "/dev/null/invalid/path"}
	_, _, err := makeLogWriters(&opts, "container1", "gr1")
	tmpDir := t.TempDir()
	// create a regular file and then try to use a path under it as FilesLocation;
	// this is guaranteed to fail when attempting to create a directory.
	invalidParent := filepath.Join(tmpDir, "not-a-dir")
	err := os.WriteFile(invalidParent, []byte("x"), 0o600)
	require.NoError(t, err)
	opts := cliOpts{
	EnableFiles: true,
	FilesLocation: filepath.Join(invalidParent, "subdir"),
	}
	_, _, err = makeLogWriters(&opts, "container1", "gr1")

[Copilot]

activate still uses log.Fatalf when AddEventListener fails, which will terminate the whole process from inside the discovery component and bypass caller error handling/cleanup. Since similar paths were changed to return errors elsewhere in this PR, consider propagating this failure back to the caller (e.g., have NewEventNotif/activate return an error or send an error event) instead of exiting.