[fateeand]

Overview

Scenario records get an optional sessionElapsed field: milliseconds since the RUM session started, which survives reloads. The RUM client keeps no start time, so the RUM sink records it and the scenario reads it back.

Key Changes

• Recording the start (UwtRumTelemetrySink):
  • the metadata hook sees the client's own session_start event and records the moment, which covers a session starting after 30 idle minutes or on sign-out;
  • the client can also start the first session inside its constructor, before the hook exists. The sink then notices the session cookie (cwr_s, or cwr_s_<id> with unique) appear and records that moment instead. It only checks that the cookie exists, never its contents;
  • nothing is recorded while cookies are off, because the session ends with the page;
  • a guard stops the recursion that a sessionLengthSeconds of 0 would cause.
• Storage (uwt-session-start.util): one localStorage entry, ngx-ui-watchtower.sessionStarts, holding the five most recent session ids with their start times. Five, because tabs can drift onto different sessions. It never throws: blocked storage, corrupt values and non-finite times are all handled.
• Reading it (UwtScenario): toRecord() looks up the record's own sessionId and sets sessionElapsed, or leaves it out.
• Fragments: a fragment gets the shell's session id through the identity handshake and finds its start in the shared localStorage (a Web Fragments iframe is same-origin and unsandboxed), so fragment and shell records sit on the same timeline.
• Public API: uwtMarkSessionStart(sessionId), so a custom destination that owns its sessions can record starts too. The reader stays internal.

When the field is absent

The field is left out rather than guessed when:

• there's no session yet, or no destination that records starts (the noop sink, an older shell version);
• suppressSessionStartEvent is on, cookies are off, or localStorage is blocked;
• the session began on a page in pagesToExclude, or before this version was running;
• two tabs start sessions at the same instant and one overwrites the other's entry.

Impact on consumers

• No change needed. The field is optional and elapsed keeps its meaning.
• Micro-frontends: the shell has to run this version with the RUM sink; web fragments need nothing.

Closes #19

[github-actions]

Coverage report

St.❔	Category	Percentage	Covered / Total
🟢	Statements	97.12% (+0.14% 🔼)	1280/1318
🟢	Branches	95.27% (-0.13% 🔻)	705/740
🟢	Functions	96.95% (+0.12% 🔼)	318/328
🟢	Lines	97.48% (+0.12% 🔼)	1237/1269

Show new covered files 🐣

St.❔	File	Statements	Branches	Functions	Lines
🟢	... / uwt-session-start.util.ts	100%	96%	100%	100%

Show files with reduced coverage 🔻

St.❔	File	Statements	Branches	Functions	Lines
🟢	... / uwt-rum-telemetry.sink.ts	95.83% (+0.6% 🔼)	91.96% (-0.59% 🔻)	93.88% (+0.85% 🔼)	97.31% (+0.42% 🔼)

Test suite run success

741 tests passing in 24 suites.

Report generated by 🧪jest coverage report action from f348d04

[Copilot]

🟡 Changes recommended

The RUM sink can record a session start despite suppressSessionStartEvent, contradicting the documented behavior.

1 open issue

• Respect session-start suppression in constructor fallback · New

What changed in this PR

Adds optional sessionElapsed timing to scenario records by persisting RUM session start times across reloads and fragments while preserving the existing elapsed field.

Changes:

• Adds resilient localStorage-backed session-start tracking and exports uwtMarkSessionStart.
• Populates sessionElapsed from the record’s session ID.
• Integrates session detection into the RUM sink and adds tests and documentation.
• One moderate issue remains: the initial cookie-detection fallback does not honor suppressSessionStartEvent.

File	Description
projects/​ngx-ui-watchtower/​src/​public-api.ts	Exposes the custom session-start marker API.
projects/​ngx-ui-watchtower/​src/​lib/​utils/​uwt-session-start.util/​uwt-session-start.util.ts	Stores recent session starts and calculates elapsed time.
projects/​ngx-ui-watchtower/​src/​lib/​utils/​uwt-session-start.util/​uwt-session-start.util.spec.ts	Tests storage, retention, invalid data, and blocked storage.
projects/​ngx-ui-watchtower/​src/​lib/​sinks/​uwt-broadcast/​uwt-broadcast.spec.ts	Verifies fragment records use the shell session timeline.
projects/​ngx-ui-watchtower/​src/​lib/​scenario/​uwt-scenario/​uwt-scenario.ts	Adds sessionElapsed during record creation and renames duration state.
projects/​ngx-ui-watchtower/​src/​lib/​scenario/​uwt-scenario/​uwt-scenario.spec.ts	Tests known and unknown session timing behavior.
projects/​ngx-ui-watchtower/​src/​lib/​models/​uwt-scenario.models/​uwt-scenario.models.ts	Defines and documents the optional record field.
projects/​ngx-ui-watchtower/​rum/​src/​lib/​uwt-rum-telemetry.sink/​uwt-rum-telemetry.sink.ts	Detects RUM session starts and persists their timestamps.
projects/​ngx-ui-watchtower/​rum/​src/​lib/​uwt-rum-telemetry.sink/​uwt-rum-telemetry.sink.spec.ts	Tests RUM session-start detection and cookie behavior.
projects/​ngx-ui-watchtower/​DESIGN.md	Documents session timeline semantics and storage behavior.

_{Review effort: Lite}

[Copilot]

🟢 Approval recommended

The remaining unique-cookie-path test coverage note is a non-blocking nit.

No open issues 🎉

1 resolved since last review

• Respect session-start suppression in constructor fallback

_{Review effort: Lite}

[TerranceKhumalo-absa]

LGTM