Re-measure after wave 3, and write down the two kinds of gap it had to separate

92.8% line (2183/2352), 81.3% branch (1091/1342), 584 JVM tests in 87 classes, measured
2026-09-02 on the tree this branch creates rather than quoted from a PR body.

The shape of the wave is worth more than the number, and it is different from the two
before it. Waves 1 and 2 were finding uncovered code; by wave 3 there was little of that
left, so the gaps had to be sorted before any test was written. Coverage gaps -- filtered
to sites where JaCoCo reports mi > 0, which is what separates a real gap from a partial
branch on a compound condition, and which cut the candidate list roughly in half. And
assertion gaps, where JaCoCo is green and nothing checks the answer: MainActivity's rail
and bottom bar were both executed and transposing them passed the entire suite, as did
swapping the two progress-notification strings and swapping Content's two destinations.
No coverage number would have found any of the three.

Naming the required mutation per ticket earned its keep three times, each recorded with
what the weak assertion actually was. Also recorded: a green mutation is only evidence
when the mutation is a real change -- one classify reordering was semantically equivalent
for every reachable input, and a bad mutation and a weak test look identical in the output.

Two entries came back as not gaps, which is a result rather than a shortfall:
ContainerCapabilities:282's exclude filter cannot drop anything, and probeForConcat's
catch arm is unreachable on this runtime -- Robolectric's MediaExtractor never throws from
setDataSource, measured across four input shapes.

Both denominators moved, in opposite directions and for different reasons, so they are
stated rather than folded into the percentage: 1340 -> 1342 branches from MediaProbe.merge,
2348 -> 2352 lines from the ConcatJoiner interface. Neither is new untested code.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Recovered onto main after hitting #160's trap for real. #189 was opened against
test/concat-engine-seam and, unlike #184-#188, never retargeted to main before merging --
so it merged into a branch that had already been merged and left behind. GitHub reported
`merged`, the PR shows MERGED, and none of it was on main: `git merge-base --is-ancestor`
is what said so, one line, immediately.

That check is the entire reason this was a five-minute recovery rather than a coverage
entry that silently stayed three points stale. The failure mode is exactly what CLAUDE.md
warns about; what it did not say, and now would, is that the auto-retarget it describes
belongs to GitHub's stacking feature, so a stack opened with plain `gh pr create --base`
has to be retargeted by hand for every single PR -- and missing one is invisible until you
check ancestry.

Numbers re-measured on this tree with --rerun-tasks rather than inherited from the branch
they were taken on: 584 tests, 0 failures, 2183/2352 line, 1091/1342 branch. Same figures,
earned again.

CLAUDE.md

@@ -130,9 +130,9 @@ install for code that can never run — and on API 37 the full APK does not fit
 - The `model` package is excluded from `ReturnCount` and `CyclomaticComplexMethod` only. It is the
   decision layer, where one branch is one documented user-visible outcome and the metric counts
   answers rather than complexity. Every other rule still applies there.
-- **Coverage is reported, not gated** — **88.9% of lines (2087/2348), 75.4% of branches
-  (1011/1340)**, measured 2026-08-29 with `./gradlew :app:jacocoTestReport`, against 546 JVM tests
-  in 76 classes.
+- **Coverage is reported, not gated** — **92.8% of lines (2183/2352), 81.3% of branches
+  (1091/1342)**, measured 2026-09-02 with `./gradlew :app:jacocoTestReport`, against 584 JVM tests
+  in 87 classes.
 
   **Every figure this file carried before 2026-08-24 was an artifact, roughly half the real one.**
   Robolectric loads classes through its own sandbox classloader with no source location, JaCoCo
@@ -174,6 +174,66 @@ install for code that can never run — and on API 37 the full APK does not fit
   denominator shrank is not the same claim as one that rises because more branches are tested, and
   this entry has a history of explaining its own numbers wrongly.
 
+  Then wave 3 (#167-#178) on 2026-09-02 — 88.9% -> 92.8% line, 75.4% -> **81.3%** branch, 546 ->
+  584 tests, in ten PRs from #179 to #188.
+
+  **Its shape is different from the two before it, and the difference is the thing to carry
+  forward.** Waves 1 and 2 were finding uncovered code. By wave 3 there was not much of that left,
+  so the gaps were sorted into two kinds before any test was written:
+
+  - **coverage gaps** — the line never executes. Filtered to sites where JaCoCo reports `mi > 0`, a
+    concrete instruction no test runs, which is what separates a real gap from a partial branch on
+    a compound condition. That filter cut the candidate list roughly in half and was right to.
+  - **assertion gaps** — JaCoCo is green and nothing checks the answer. `MainActivity`'s rail and
+    bottom bar were both *executed* by `AppRootRestorationTest` and **transposing them passed the
+    entire suite**; so did swapping the two progress-notification strings, and swapping `Content`'s
+    two destinations. No coverage number would ever have found any of the three.
+
+  So **every ticket named the mutation that had to go red, and that was its acceptance criterion
+  rather than a coverage delta**. It caught **two vacuous tests written in the same session**,
+  before either shipped:
+
+  - a `firstContainerHolding` test asserting a refusal still offered *something*. True, and
+    useless: the source container is a candidate in its own right, so the list stays non-empty
+    whatever the fallback does. What it actually buys is the codec the user asked for.
+  - a staged-delete test scanning for a `"join-"` prefix `StagingNames.forJob` does not produce —
+    it names files `<jobId>.<ext>`, so the assertion was true of everything.
+
+  It also corrected a *third* test that was not vacuous: `probeForConcat`'s KDoc claimed to drive
+  the `catch` arm, and rethrowing from that catch left it green. That is how the arm turned out to
+  be unreachable — see the next paragraph. A passing test with a wrong explanation is its own
+  failure mode.
+
+  **A green mutation is only evidence when the mutation is a real change**, which is the mirror
+  trap: one `classify` mutation stayed green because reordering two arms was semantically
+  equivalent for every reachable input. A bad mutation and a weak test look identical in the output.
+
+  Three things came back **not as the ticket described them**, which is a result rather than a
+  shortfall:
+
+  - `ContainerCapabilities:282`'s `exclude` filter **cannot drop anything**. `repair` always
+    changes a codec on the shared container — a codec it left alone is one `validate` would not
+    have refused — and the one non-default `exclude` carries `COPY` while every candidate carries
+    `NONE`. F4-shaped.
+  - `probeForConcat`'s catch arm is **unreachable on this runtime**. Robolectric's `MediaExtractor`
+    never throws from `setDataSource`, measured across an unregistered `content://` authority, a
+    missing `file://`, a file of garbage bytes and an `http://` URL — all four returned with
+    `trackCount = 0`. It stays device-only.
+  - `JobSnapshots:31`'s missed arm was **not** the `!isFile` one the ticket named — that is already
+    covered by the `reclaimed` fixture. It was `path == null`: a job carrying no output path at
+    all. Read the report, not the ticket, when the two disagree.
+
+  One item was **included against** the F4 rule rather than exempted by it, and the distinction is
+  worth having written down since both live in the same function: `ContainerCapabilities:94`
+  (`accepts(container, VideoCodec.NONE, mode)`) is dead in production today — every caller guards
+  `NONE` first — and was tested anyway, because its audio twin at `:101` has had a test since #136
+  and the asymmetry was the argument. The `COPY -> error(...)` arms beside it stay exempt, because
+  a second line of defence that can be provoked is not one.
+
+  Denominators moved here too, in both directions and for two different reasons: 1340 -> 1342
+  branches from `MediaProbe.merge`, 2348 -> 2352 lines from the `ConcatJoiner` interface. Neither
+  is new untested code.
+
   And **re-measure before quoting**: this entry was once written quoting 81.4%, measured four hours
   earlier, and was already three points stale by the time it was ready to merge.
 - **Testable code is not done until it is tested.** If a piece is unit testable, it gets unit