ww output: match Go exact -o parsing

docs/spec.md

@@ -344,7 +344,19 @@ ImportPath    = ident { "." ident } .
   arguments and result; this rule does not adopt Go's source signature. An
   ordinary import of a package declared `main` is rejected, except for the
   toolchain's colocated external-test wiring.
-- For `ww build`, an explicit `-o` names an output directory when ordinary
+- For `ww build`, the output-option name is exactly `o`. The accepted forms are
+  `-o VALUE`, `--o VALUE`, `-o=VALUE`, and `--o=VALUE`. An equals form splits
+  at its first `=` and preserves every later byte, including further `=`
+  characters; an empty value is valid. Repetition is last-value-wins, and a
+  final empty value means that there is no effective explicit output, so the
+  ordinary default-output or no-public-output rule applies. A concatenated
+  spelling such as `-oVALUE` or `--oVALUE` is an unknown flag, not an output
+  option. Build option parsing stops at the first package or source operand;
+  later flag-like arguments remain operands and are not reparsed as `-o`.
+  These spelling and placement rules select only caller-visible output
+  disposition and never supply package, import, graph, action, symbol,
+  artifact, `.wwi`, or persistence identity.
+  A nonempty effective `-o` names an output directory when ordinary
   `stat` reports an existing directory (following symlinks) or its spelling
   ends in `/`. This classification is independent of whether one or many
   package roots were requested. Each selected command is published beneath
@@ -771,11 +783,22 @@ coordinator reports that successful validation exactly as
 `?    <package> [no test files]\n`.
 
 Every test-bearing directory product links one request-private runnable.
-`-c` retains an executable copy and suppresses its execution; `-o` retains a
-copy at the named destination and still executes unless `-c` is present. With
-no explicit output, `-c` writes `<import-leaf>.test` in the invocation
-directory. An output ending in `/` or naming an existing directory receives
-that basename and may have missing parent directories created. One
+The test output-option name is exactly `o`, with the accepted forms `-o VALUE`,
+`--o VALUE`, `-o=VALUE`, and `--o=VALUE`. Equals forms split only at their
+first `=` and preserve an empty value or any additional `=` bytes. Repeated
+occurrences are last-value-wins. A final empty value means no effective
+explicit output and therefore requests no running-test retention; with `-c`,
+the ordinary default retained name applies. A concatenated `-oVALUE` or
+`--oVALUE` is unknown. Unlike build option parsing, known test options,
+including these exact output forms, are recognized before or after package
+operands. Invalid output-option names reject before package loading, product
+construction, execution, or publication.
+`-c` retains an executable copy and suppresses its execution; a nonempty
+effective `-o` retains a copy at the named destination and still executes
+unless `-c` is present. With no effective explicit output, `-c` writes
+`<import-leaf>.test` in the invocation directory. An output ending in `/` or
+naming an existing directory receives that basename and may have missing
+parent directories created. One
 non-directory output may name only one package. Multiple packages whose
 visible import leaves would produce the same test-binary name reject before
 tools or output creation; exact `/dev/null` is the discard exception. It keeps