Silence-driven progress heartbeat renderer for SimpleAnsi/NoAnsi terminal modes

[Evangelink]

Summary

Implement the silence-driven progress heartbeat renderer for the SimpleAnsi and NoAnsi terminal modes. This is the core implementation of #9125 and the natural successor to #9138.

Background

Today, TerminalOutputDevice.cs:212-216 force-disables progress for SimpleAnsi/NoAnsi, leaving CI / piped / file-redirected runs with zero progress signal between the banner and the summary. Previously the platform emitted a per-DLL summary every 3 seconds, which was rejected as spam (#6753). The fix is event-driven, not time-driven.

Design

The terminal reporter picks a renderer based on capability:

AnsiMode	Renderer
AnsiIfPossible / ForceAnsi	existing cursor-redraw renderer (unchanged)
SimpleAnsi / NoAnsi	NEW silence-driven heartbeat renderer

Three independent emission rules. Each produces single lines, no cursor tricks, no duplicate timestamps (CIs already prepend their own):

E1 — silence heartbeat

Emit one summary line only when no test completion event has occurred for N seconds (default 30s). A healthy fast suite emits zero heartbeat lines.

running … 312/3200 completed, 2 failed | active: SlowTest.Foo

E2 — slow-test surfacing

When a single test exceeds a per-test threshold (default 60s), emit one line with exponential backoff (60s → 2m → 4m → 8m …):

[slow] still running after 60s: SlowTest.IntegrationFoo (MyAcceptance, net9.0)

E2 fires in all modes (including cursor) because it leaves a durable scrollback line; cursor frames are transient.

E3 — failures inline

Verify failures continue to be printed at the moment of failure for SimpleAnsi/NoAnsi. Already true in cursor mode; mostly a verification item.

Gating

• Renderer is selected when --progress (Add --progress {auto|on|off} and deprecate --no-progress in MTP terminal reporter #9138) resolves to on AND AnsiMode is SimpleAnsi/NoAnsi.
• --progress off (or legacy --no-progress) suppresses everything.
• Test-host controller / --list-tests / server mode continue to suppress.

Knobs (env vars only, no new CLI flags)

• MTP_PROGRESS_SILENCE_SECONDS (default 30; 0 disables E1)
• MTP_PROGRESS_SLOW_TEST_SECONDS (default 60; 0 disables E2)

Extension hook

Introduce a minimal IProgressEnricher (name TBD) hook with:

• OnAssemblyStart(asm) / OnAssemblyEnd(asm) — per-CI extensions emit group markers here.
• OnFailure(test, …) — per-CI extensions emit native annotations.
• OnSlowTestThreshold(test) — extensions can lower/raise per-test E2 threshold (powers the AzDO-history extension).
• OnSlowTestEmit(test, currentDuration) — extensions can decorate the emitted line (e.g. with historical p95 = 2s).

The hook contract is shipped here so per-CI extensions can iterate independently.

Touchpoints

• src/Platform/Microsoft.Testing.Platform/OutputDevice/TerminalOutputDevice.cs — collapse the if (noProgress || ansiMode is NoAnsi or SimpleAnsi) branch to just if (noProgress); renderer picked by AnsiMode.
• src/Platform/Microsoft.Testing.Platform/OutputDevice/Terminal/TestProgressStateAwareTerminal.cs — extract renderer abstraction.
• New: SilenceDrivenHeartbeatRenderer.cs (or equivalent).
• New: IProgressEnricher hook + glue.
• Tests: heartbeat fires only on silence, slow-test backoff math, failure inline, --progress off suppression, controller suppression, env-var overrides.
• Acceptance: re-run HelpInfoTests / HelpInfoAllExtensionsTests (no new flag here, but verify nothing regressed).

Out of scope (deliberately)

• The CLI flag rename itself — Add --progress {auto|on|off} and deprecate --no-progress in MTP terminal reporter #9138 (prerequisite).
• Per-CI extensions (groups, annotations, GH GITHUB_STEP_SUMMARY) — separate issues per package.
• AzDO history-driven slow-test thresholds — separate issue (extension hooking into E2).

Related

• Add CI-friendly textual progress heartbeat to MTP terminal reporter (raw log progress signal) #9125 — parent design discussion.
• Add --progress {auto|on|off} and deprecate --no-progress in MTP terminal reporter #9138 — --progress flag rename (prerequisite).
• Test duration is added instead of being updated (every second) #6753 — historical rejection of fixed-cadence heartbeats; this design avoids that trap by being silence-driven.
• Show slowest tests #3495 — slowest-test detection; this issue establishes the emission point; the history-aware version is a follow-up.